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Slick Roads: Newsletter Challenge (03/02/10)

Posted February 28, 2010 5:01 PM

This month's Challenge Question:

You live in the Northeast area of the U.S., and you drive a manual-shift car. If it's been snowing and the driving conditions are slippery, will you have better traction by starting your car's motion in first or second gear?

The Answer will be posted right here on CR4 on April 6. Can't wait that long? Well, check out these weekly challenges from CR4:

The Weight Lifter: CR4 Challenge (02/16/10)

Banked Highway: CR4 Challenge (02/09/10)

Power Lines: CR4 Challenge (01/26/10)

Unstable Picture: CR4 Challenge (01/19/10)

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#1

Re: Slick Roads: Newsletter Challenge (03/02/10)

02/28/2010 7:45 PM

It doesn't matter for the actual traction. But, you'll get better traction control starting in second gear since you will, in effect, have a lower gain for the feedback from your gas pedal foot to the torque of the drive wheels. That is, you can give it a little too much gas, or hestitate a millisecond too long in letting up on the gas, and still not generate enough torque to break free, thus switching from (almost) static friction to a lower kinetic friction.

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#2

Re: Slick Roads: Newsletter Challenge (03/02/10)

02/28/2010 8:46 PM

I was taught to put it in high gear, give it plenty of gas and slip the clutch, it's not good for the clutch but it is the way that produces the slowest acceleration (least torque).

Clearly, 2nd gear.

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#3

Re: Slick Roads: Newsletter Challenge (03/02/10)

02/28/2010 9:32 PM

I have driven manual cars all my life, grew up in the North East, and consider myself an expert driving on snow and ice with over 30 years experience in manual cars without traction control.

Like most things, this challenge has two components. One is the torque applied to the rear wheels is lower in higher gears. The other is the reality of driving in slippery conditions.

The correct answer for the challenge is probably a higher gear because the rear wheel torque is less and the trick is to not break the static coefficient of friction... Regardless, it requires good throttle technique.

The reality is, that the whole secret to driving in slippery conditions is to be smooth. This means that starting in first gear is fine and actually preferred, but you must be slow and smooth with the clutch and the throttle. In other words, it requires finesse. The same goes with shifting between gears.

If driven competently, there is no reason to not use first gear at a start and I would train anyone learning to drive to do it that way. It reinforces the idea of being smooth and those lessons apply too snow, ice, wet, and dry conditions when driving.

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#4
In reply to #3

Re: Slick Roads: Newsletter Challenge (03/02/10)

02/28/2010 10:56 PM

Yes.

I was much more likely to use second in a heavy automatic transmission car, than second in a clutch car.

You are going to wear somewhere, and the automatic fluid transmissions are actually stronger.

I hate to lug an engine and feel rods bending.

Short heat on the clutch is better than breaking the engine.

Really only time I moved out in second on snow and ice was in cars with automatic transmissions.

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#5
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 12:44 AM

I don't understand; don't automatic transmissions always start in first gear and then upshift automatically? Selecting low or second gear limits how high it shifts, not how low.

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#18
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 10:43 PM

Tornado,

I cannot speak for all manufacturers on this, but GM cars will start in "second gear" if you select 2nd. (or "S" in the older automatics).

from what I understand, it was specifically designed this way, to allow more controlled traction in slippery conditions.

I travel a lot, and subsequently abuse... errr.... test drive a lot of rental cars.

most of those rentals seem to have this feature as well.

try it on your car... most likely it has this feature, and you just missed it when you read the owners manual front-to-back before driving your car..

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#67
In reply to #18

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 10:14 PM

Thanks! Interesting to know, and it looks like a good design idea. Now if I can just remember it long enough for next winter....

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#83
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 5:57 PM

The norm, I would estimate, is now that second will start you off in second. My 1996 Honda Odyssey is this way and most other more recent cars I've owned or played with have been this way too. Even quite old Mercedeses were this way also. But in the days of three-speed automatics, selecting second would cause you to start in first and not go beyond second.

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#132
In reply to #83

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/10/2010 8:41 AM

Generally, '60s through late '80s Ford three speed automatics allowed you to select 2nd AND start in 2nd. GM and Chrysler transmissions did not. The GM and Chryslers would just limit how far up the tranny would shift. I've owned and driven many of each. At least some Volvos built in the last 15 years have a "Snow Mode" for the tranny. It's an admirable feature that starts them in 3rd gear, which REALLY reduces the torque. Some modern very powerful luxury cars WILL always start in second, utilizing first only if you floor it. These are the rare exception, though, and this won't help you in snow as much because of their vast power.

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#172
In reply to #132

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/30/2010 10:09 PM

Hello, the question was about manual gearboxes! why are you commenting on automatics.. lost the plot.....thought this blog was for the intelligent.

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#88
In reply to #18

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/04/2010 8:30 AM

johnnybravo I have a tendency to read magazines, owners manuals, but not books from the back quite often. I guess I think I will miss something reading from the front because I will get bored and not get to the back.

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#10
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 11:29 AM

I would agree with this provided that the clutch provides uniform friction as the plates rotate relative to each-other and also there is no stiction in the control linkage to the clutch. In practice, however, nothing is perfect - and second (or higher) gear allows more margin for error.

If you know you can get away with first gear, it is the best one to use. However, if in doubt use a higher gear - the wear on the car (and on your temper) trying to get moving if you've once failed will almost certainly be worse than the wear you will cause by slipping the clutch one time in a higher gear.

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#13
In reply to #10

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 1:08 PM

P.S. If the car is front-engined and rear-wheel-driven, I recommend bag of cement in the trunk when these conditions are expected. If unexpected, get helpers to sit in the trunk.

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#147
In reply to #13

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/16/2010 3:08 PM

It's also a good place for back seat drivers.

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#28
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 7:55 AM

Here, here.

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#29
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 8:50 AM

The Anonymous Hero is MY HERO!

What gear you run with is supremely unimportant. SMOOTH is the key. No one seems to get that, and if you are not used to driving in snow (or are a slow learner), write that word in all caps and paste it to the top inside of your windshield where it does not get in the way for seeing. Read it every time you get in the car. Live it - Love it.

Every car I have seen in the ditch this winter has broken that simple one-word rule! If you are going to turn, stay off the gas. If you are going to stop, DON'T turn. You only have so much traction to work with, and acceleration, deceleration, and turning all use up traction. SMOOTH reduces the amount of traction used. Sudden hits (gas, break, or hard turn) gobble up every ounce of traction you have. Speed is not important (I have passed cars in the ditch at 70 mph that I know got there doing less than 50), panic control is everything. If you have plenty of space around you (yes - stop tail-gaiting), you don't need to use the breaks as hard or steer as sharply when the crap hits the fan. Drive SMOOTH!

So to answer the question, you can drive in any gear if you are smooth. If you are a putz, go ahead and use 2nd to start (as all "instructors" will tell you) - it will give you a little more margin for error. However, you will also get going faster, quicker, and will get yourself over your head sooner - resulting in a face to face meeting with the next guardrail. I have been driving in Wisconsin winters for 24 years, and have gotten into trouble twice - once I used up my breaking traction (as my mother was screaming to do so while I kept the car under control), and once I was confronted by sheer ice in the fog and simply overshot my turn. Both were over 22 years ago, and then I learned to conserve traction for "just in case". All of those years I was driving stick-shifts, and all those years I started out in first gear with no ill effects.

Final pet peeve: You SUV/Truck Drivers - leave your truck in 2 wheel drive until you get stuck - then put it back as soon as you get out. 4 wd does not do you any good on the road. The tires NEVER spin at exactly the same speed, so they unnecessarily burn up traction on slick roads, and play hell on the drive train on hard-top. Most importantly - they do NOT help you stop when the time comes. Sure you can get going faster, but you are much more unstable at those speeds, and you have already used up half your traction just to maintain where you are. If you need to hit the breaks, you have no traction left, you will slide across both lanes, bounce off of my car, and send us both into the guardrail. My car will be wrecked, but right side down, while your truck will be rolled over the guardrail and sitting on top of you with the wheels UP.

More than 75% of the vehicles I have seen in the ditch in my lifetime where SUV's and at least 75% of those were upside down. Invariably the cars are driven by young kids, and they are facing the wrong way on the road edge after a 180 in the middle of it. People panic, and it is all over!

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#30
In reply to #29

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 9:14 AM

Amen to most of that about SUVs.

But I hate FWD cars in the snow, too. We had two--both Auroras--and their handling in snow and ice was abominable. With a RWD car, handling is predictable. When it's sideways or sliding or locked up under braking, a RWD is controllable. You can get on the gas to bring the rear out, lift off the gas to slow it down, make the tire edges bite with a Scandavian flick, dance around corners on the hairy edge of tractiion, and perform a lot of emergency manuevers that are instinctive and actually work.

A FWD car does not obey any of the laws of physics. Instead, it just plows off the road, no matter what you do. Brake! That didn't work. On the gas! That didn't work. Steer into the skid! That doesn't work either. All you can do when a FWD car slides is slam on the brakes and brace yourself for the impact.

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#33
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 9:33 AM

That is not universally true. The reason it appears so is that the suspension on most SUVs is not designed - or if it is designed it is not for use on the road. Given equivalent tires, an Audi Quattro (for example) will out-perform most 2-wheel drives on almost any surface. And no, I don't drive one - I've never found the extra traction necessary (wimp?), so I don't see any point in paying the extra money (neither for purchase nor for fuel)

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#55
In reply to #33

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:52 PM

I agree with guest,

I am driving my first 4 wheel drive pickup truck (a Mazda B4000 with 32 inch tires, its like a ford ranger). This winter I got to play in several types of snow covered roads. The packed frozen snow/ice was the easiest to drive in, the 4 wheel drive kept me moving and all the frozen snow did was make the ride bumpy. The next was a very wet slushy mess that acted like driving through a 2 to 3 inch puddle. I was in a hurry and passed everyone (on a 4 lane highway) by going into the unplowed lane. It was fine till I was undertaking (passing on the inside) an 18 wheeler and the slush hydroplaned me right into the ditch. As I slid about half sideways, I turned into the slide and kept on the gas until the truck was at an angle enough that the 4 wheel drive pulled me back onto the road. It was interesting to be sliding to the right (because of camber) while the wheel was turned about 1/4 to the left.

Had I been in a front wheel drive I would have turned the wheel a bit more left and started fluttering the pedal to try to grab and loose grip as much as possible until I pointed back to the road, in a rear wheel drive I probably would have been hosed unless I had enough speed to ride into and out of the ditch.

For the most part as I experimented between 4 and 2 wheel drive with no weight in the back of my truck, I noticed that in 4 whd the truck did not fishtail and instead behaved when pulling off from traffic lights. Also, for slowing down, using down shifting was much better for control because all wheels stayed rolling instead of locking up; so I could still turn while slowing.

Drew

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#75
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 10:27 AM

I totally disagree driving FWD during Norwegian winters during more than 50 years, starting with SAAB 2-stroke engines in the sixties, and trying VW BWD one winter, in my experience the FWD (now a Citroen 2.5 liter) is totally superior to BWD during winter driving.

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#76
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 10:35 AM

Gotta respect a Norweigan's opinion, especially somebody who drove a Saab 96. I guess if you've driven FWD all your life, you learn to respect its quirks. As for me, no thanks. FWD is too weird for me. I'll take RWD or AWD over FWD any day. Wonder what a VW BWD is? Backwards drive?

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#77
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 11:38 AM

Bad wiggle drive?

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#89
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/04/2010 9:49 AM

Of course, FWD and RWD cars can both be controlled on slippery roads. The Monte Carlo rally was, for a long time, a showcase for FWD cars beating the pants off RWD in slippery conditions.

Any FWD car can be smoothly and predictably altered, by driver input, from near oppressive understeer to dramatic oversteer. It's just a matter of left foot braking, in which you simultaneously apply throttle and brake (a more precisely modulated version of the handbrake turn). Lots of throttle and lots of brakes =

  • a. Front wheels rolling along, balanced at near neutral drive force, and therefore having ample grip for cornering.
  • b. Rear wheels attempting to retard the car, with almost all their traction used up in so doing, leaving precious little for keeping the back behind the front.

Your Auroras may have had other virtues, but handling (on any road surface) is not among them. (Even though your Olds was not technically your grandfather's Olds, Oldsmobiles are incapable of doing anything other than going in a straight line, and any degree of steering feedback was considered a curse by Olds engineers.) GM has done some great things (although I can't recall any other than having produced the Corvette, one of the best "branding" efforts in history and fun to drive in a crude sort of way) but they do not produce cars that "handle" in any sporting sense of the word. The GM official test of "handling" consists only of executing a parallel parking maneuver.

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#92
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/04/2010 11:21 AM

There's a huge difference between a rally-prepped FWD and a street FWD. The big thing is that rally cars have a limited slip diff. A street car acts differently, depending on which way you turn it. Some will spin a front wheel on right turns but not lefts, others will spin on lefts but not rights. Rally cars don't have this problem.

I do a little instructing for race cars, specializing in AWD vehicles. I asked some of my fellow instructors about instructing in FWD cars, but decided that their idiosyncracies were too much too fool with. I'll leave FWD instructing to the experts.

Your point is well taken, though. A properly set up FWD car CAN outperform an AWD car from the same make. The primary reason is the weight reduction.

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#94
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/04/2010 11:35 AM

Haven't you seen the Olds gangster films? the ones where the driver is twitching the wheel all over the place. That was the only way to get an Olds to go in a straight line. As for bends, they are what you get if you stay down too long and come up too fast.

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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/04/2010 12:04 PM
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#144
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/16/2010 12:57 PM

Not all GM FWD cars are poor handlers in slippery conditions. The best car in snow that I ever drove was the 1981 Chevy Citation. It had other faults, including a flaky and fragile choke system, but it was much easier to handle than RWD when the white stuff got deep on the roads. The FWD Buicks I've had did alright provided I limit the rate of acceleration, as advised by others who have posted on this forum.

A bicycle in snow is a different proposition. You MUST start in a low gear, otherwise the sideways force from your leading foot will slide the bike into your standing leg instead of providing forward motion. (I only had to learn this once!) Biking in snow is a great way to learn the limits of acceleration rate under slippery conditions, but I strongly recommend wearing a helmet and insulated (padded) clothing to reduce the chance of being injured in a wipe-out.

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#125
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/09/2010 2:38 PM

FWD cars are actually quite predictable. My wife is a champion horse and cart driver and I taught her in an instant how to drive the FWD vehicles without mentioning torque, coefficients of friction, momentum, etc.. Just imagine that the front wheels are the horses. To get going on slippery stuff, you move as gently as possible so the horse doesn't skid and fall. In the FWD car, you move as gently as possible so the car doesn't spin the wheels and go sideways. When you are going around a corner, you keep the horses pulling out in front so the cart doesn't try to overtake the horse by swinging to the outside of the corner and take the horse with it. In the FWD car, you keep the front wheels pulling (and the front in front) by keeping on the gas to maintain your speed - never back off the gas or brake.

I use second gear to get going on ice. Although I can do it in first, it's easier in second because it puts less torque to the wheels and provides more subtle control.

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#148
In reply to #30

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/16/2010 3:14 PM

Suggest you read, re-read and then read again the word 'Smooth'. I drove a 72 Subaru for nearly 10 years in all weather - as long as I was smooth, no problem. Only feel free to slam on brakes IF you have a good ABS. Drive safe and smooth.

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#53
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:41 PM

Frank,

I like your example, I use a similar model when considering traction available when cornering on my bike. I know that I have several choices when cornering; go through at fastest speed where all grip is for holding the road or go through with some grip left over for braking or accelerating (there are other considerations too but don't apply here).

The point I am making is you have a delicate balance between grip and slip. You can use your available grip for what you need as long as your total use does not exceed available grip. I look at it as a balance scale with grip on one side and use on the other.

Drew

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#31
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 9:22 AM

Best to drive as you would normally (sorry, living in New England doesn't of necessity confer expertise except in one's own mind).

Much is said about torque and friction, but one must realize the extent and degree to which these are irrelevant matters. The mechanical advantage conferred by the lowest gear (that is, mechanical advantage to start the vehicle weight in motion, not order to spin wheels faster [after all...once friction is lost torque and gear are of no use.) Here's an analogy: one would never say that in order to start a stick shifted vehicle in motion up a hill, one should skip first gear... But, that is essentially what you are saying here...obviously, starting up a hill, where the car weight wants to go back down, using (say) second gear (provided no stall [as would not be a problem case in the icy road situation] would tend to simply make the drive wheels turn faster due to lower gear ratio...and spinning wheels do nothing to gain traction up the hill...in fact reduces traction because the treads lose contact with the earth.

I similar fashion, faster turning of drive wheels tends more to assure loss of traction and even less impediment to spinning of wheels. What you want is the gear selection that both applies the maximum mechanical advantage (that's force) to start the car weight in motion (not a matter of fast motion, just motion) and does so with least likelihood (least drive wheel speed [gear ratio set not for speed but for force) of overwhelming and losing friction at road surface...that is, the lowest gear...because there is a direct relation between the likelihood of breaking of traction (friction) the faster the wheels are spinning. (Remember, torque becomes advantageous only when there is a resistive force (counter action) is is provided by (say) High Friction pavement ...but is of little or no advantage when the counteracting force (as on icy pavement) is not present or only minimally and precariously present. You spoke of rear wheel drive...in that instance, attempting to start off in a higher speed gear also creates a greater differential between turning of the driver and undriven wheel...making lateral tail motion more likely.

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#32
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 9:29 AM

Oh, another thing...

Probably the most frequent cause of mishaps on snowy/icy pavements....

Because one goes to fast (and fails to have gearing set properly to use engine-brake restrain on vehicle velocity (and momentum). This is why it's always best to advance gearing selection as slowly as possible...preferring control (inherent in low gears) to speed inherent in higher gears. The real problem with snow driving is that people get in a hurry (or simply don't know better) and then place them selves in driving dynamic situation (too high a gear or overtaking) where action to correct (to avoid mishap) are of least effect...such as overreliance on wheel braking (and skidding) in order to stop.

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#35
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 9:48 AM

I beg your pardon. It sure does (as in any snowbelt state or region) as long as you actually get out and drive in it on a regular basis and "train" on slick surfaces where you have room for error. Those who don't experiment with traction (braking, turning, acceleration, crossing snow ruts, etc) won't learn anything. Besides, there aren't too many things more fun than a snow packed, wide open parking lot without curbs or lightpoles for spinning donoughts and getting used to your vehicle sliding around and how you get it back under control.

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#40
In reply to #35

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 11:53 AM

Absolutely!!!!

Take your car out and do some stupid crap with it. Learn how it feels just before you lose it totally. Then you know when to dial things back when you don't want to lose it totally. As you start to lose it, try to regain control - learn what that feels like, and what works/doesn't.

Just don't do it alone if you are a young kid and the cops are around - they just love to ruin a kid's day! Take your Dad along - leave Mom at home and never speak of it to her!!!!

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#169
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/30/2010 7:38 PM

Drive like you hold an egg between your foot and the pedals. You don't want to crush the egg and you don't want it to fall to the floor either. Better to arrive late than to deal with down time and insurances.

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#60
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 3:23 PM

Anonymous Hero has it right. While arguments can be made for second gear over first due to reduced torque output, the reality is that people who drive a stick shift know it is easier to stall an engine when starting in too high of a gear. As such, human nature tends to over-compensate for any increased advantage by using a higher throttle input. They rev the engine slightly higher and slip the clutch a little more. The key to driving in snow and ice is to make gentle transitions. Speeding up, slowing down, or turning can be done even on polished ice as long as the change is made smoothly. Lower friction between the road and the tires means that sudden changes (which require greater forces) will break them loose. For this reason, how you release the clutch is the most important part and not what gear you are in. Develop your fine motor skills and you'll be good no matter where your shifter is.

My Dad told me years ago when I was learning to drive that I needed to find a parking lot with no cars and practice putting my car into a slide and then pulling it back out. He told me that if I couldn't do both of those things, I didn't belong on the roads in the winter. He was spot on correct. Putting it into a slide teaches you how much input will upset your car....so you know what not to do. When you are driving and approaching those levels of input you know to back off to avoid getting into trouble. Pulling it out of a slide helps you learn how your car handles when your tires are no longer dictating your motion. Momentum and its tendency to spin or straighten are important to be aware of so that you can regain control. Lastly, it makes you comfortable with a car that is slides. Many accidents are caused by people who got in a little trouble and overreacted (which goes back to the first part about what input it can handle). When you're familiar with a slide, you recognize which one is dangerous and which one is controllable. You can then react accordingly and end with the best result possible....even if it's a crash at least you can mitigate the damage.

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#62
In reply to #60

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 3:36 PM

In a manual car, high throttle input is not an issue when starting in second, other than wear on the clutch. The torque required is set by adjusting the setting of the clutch, not by engine revs. The lower mechanical advantage means that second gear is less sensitive to errors in clutch setting. In an automatic with torque converter there's little chance of stalling if you've run the engine for a bit.

If you know the vehicle well and that you can manage it in first, go for it. Otherwise, second is more tolerant of vehicle unevenness, or perish the thought, driver misadjustment.

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#82
In reply to #3

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 5:47 PM

The reality is, that the whole secret to driving in slippery conditions is to be smooth. This means that starting in first gear is fine and actually preferred, but you must be slow and smooth with the clutch and the throttle.

As another yankee, I have to agree, provided the car in question has a manual transmission. In low gear, one can slowly engage the clutch even with the engine at idle, whereas in second gear most cars require some throttle (to prevent stalling) and more deft clutch work. Also, should the wheel(s) spin, first gear will cause a slower spin rate, providing a quicker return to control when the throttle is eased.

In automatics, where the torque converter absorbs and smooths engine input, starting in second gear is recommended by most manufacturers, (in cars in which that is possible) for the reasons that will no doubt be mentioned in the official answer.

Good correct answer, and unlikely to match the official answer.

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#85
In reply to #82

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 6:26 PM

That seems to be missing the point - that you should use clutch pressure to control the torque, so engine speed becomes irrelevant. The reduced mechanical advantage of second or higher gear means you can afford to be less deft with the clutch.

The other reason that second or higher gear is useful under the slipperiest conditions is that no clutch is totally even, and they can become quite uneven at low plate pressures without this being noticeable under normal driving conditions. The reduced mechanical advantage of the higher gears means you are less likely to discover this problem when you least wish it.

Nevertheless, if you have a steady foot and have already checked the evenness of the clutch, first gear is at least as good.

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#86
In reply to #85

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 9:01 PM

The reduced mechanical advantage of second or higher gear means you can afford to be less deft with the clutch.

Only in an idealized world. In the real world, it is harder to start off in second gear, smoothly, and requires application of throttle, for most people, to avoid stalling.

Engine torque is quite directly related to engine speed, at near idle speeds -- it is easy to double torque with very small throttle applications. (In contrast, under higher load, higher rpm conditions, doubling torque requires a very large change in throttle position.) In other words, the torque curve is very steep at low speeds, (and is, of course, instantaneously horizontal at the torque peak).

So leaving the engine at idle produces the least amount of engine torque, and leaves throttle out of the number of things to control. If you develop the ability to engage the clutch at idle, without applying any throttle, then with only one control, you can apply very gradually increasing torque to the drive wheels. Adding throttle control to the mix makes this more difficult for the inept. I would hazard a guess that virtually no moderately skilled driver in the northern states routinely starts out (in slippery conditions) in second gear in a manual transmission car. I have 30 years driving experience on slippery roads, and frankly even in the minority of occasions during which I was driving an automatic trans with the ability to start in second did I actually use that option -- it is simply unnecessary.

With an automatic, you have only one control, and it is harder to finesse (because of the steepness of the torque curve near idle). So then, starting in second makes sense (in cars that are new enough to permit second gear starts but not so new as to have traction control).

My Honda (manual), being something of a torqueless wonder, will start off easily with no throttle in first, but not second. Even a skilled driver will have slightly difficult time starting off smoothly in third gear, (illustrating the difficulty by making the case slightly more extreme) and smoothness is everything in driving on icy roads. If second is good, then fifth should be even better... but try to start smoothly in fifth.

On slippery roads, I frequently use throttle to sense conditions, and would rather have a spinning wheel under my own deliberate control, than be surprised by one, or be surprised by no traction for braking. This technique (which I have used on race tracks as well, to set up a slide, rather than to let one surprise me) has worked very well, with one notable exception. I was driving a car with automatic transmission (old three speed) and blipped the throttle on an on ramp as a test. (This was my first car with automatic transmission.) The car spun its tires, and sensing the reduced load from my backing off the throttle, quickly up-shifted, causing the wheels to spin yet faster. Remarkably quickly, I ended up off the road, feeling like a bit of a fool.

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#170
In reply to #3

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/30/2010 8:17 PM

If At first.first don't work....try,try...second

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#174
In reply to #170

Re: Slick Roads: Newsletter Challenge (03/02/10)

04/02/2010 12:48 PM

Too late if you've already dug yourself into a hole

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#6

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 2:20 AM

The traditional answer to this question is second gear. This answer takes into account the limitations of human reflexes and the lack of precision in controlling the torque and slip characteristics of a manual clutch.

The coefficient of static friction between tire and road, particularly if there is a deformable layer of snow which can compress to match the tread of the tires and transmit greater horizontal forces as a result, is much higher than the coefficient of kinetic friction once the tires start to slip. So it is critical to avoid slippage to the greatest degree possible.

If you put the car into first gear, the torque which the engine can deliver to the wheels at any throttle setting including idle is greater than the torque which the engine can deliver at the same engine speed and throttle combination in second gear. If the tire-to-road friction is sufficient to avoid slipping, the car can accelerate more rapidly from a stop when in first gear. And if the clutch is slipping to transmit a particular torque from the engine to the input shaft of the transmission, the corresponding torque at the wheels will that value multiplied by the gear ratio of the transmission.

When the driver's goal is to avoid exceeding the available static friction while balancing the throttle and clutch pedal, as is the case on slippery snow, the use of a higher gear limits the amount of torque which is transmitted to the wheels for a given level of clutch friction. This gives the driver a wider band of clutch pedal travel to work with in trying to keep the wheel torque within static friction limits.

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#7

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 4:24 AM

Here's a vote for second gear.

Grippy-most in the slippy-sliders!

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#8

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 7:04 AM

"will you have better traction by starting your car's motion in first or second gear?"

Traction will be the same as it is up to the operator. Traction does not change by what gear we start in. It changes in how one lets out the clutch and how the throttle is applied. So the answer is neither.

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#9
In reply to #8

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 11:21 AM

If you start too suddenly the traction will reduce (sliding versus static friction). So you can translate the question to: "which gear will give a smoother start".

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#11
In reply to #9

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 12:49 PM

Have always owned vehicles with manual transmissions. One gear will give just as smooth of a start is the other if you know what your doing. Have never incurred a slippery road due to ice or snow that first gear didn't suffice.

Maybe it also should have said "for the inexperience operator"

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#12
In reply to #11

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 1:00 PM

Try it in a 68 Camaro, 327 V8, and a less than half full gas tank.

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#34
In reply to #8

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 9:40 AM

Good...but you took the too-narrow view of things. What you want is the greatest engine mass applied to maintain greatest control (ala, engine breaking...which, in the case of snow) means not slowing, but prevention of potentially uncontrolled acceleration. Once moving the gear (say second) that is the lowest input/output force ratio is that gear (again, say second) which will least allow the engine's inertia to impart speed restraint on the rotation of drive wheels...conversely, most allow engine rotational speed to be imparted to the drive wheels. Therefore greatest control (and control is really what this discussion is about) will always be in a gear that is lowest for any speed range...and, because we are starting from zero speed, that gear will always be first gear. The dynamics are essentially the same as between ice pavement and concrete (etc) pavement. It just the parameters of control that change. Using a hight gear only serves to accentuate (to exacerbate) those dynamics of control factors.

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#14

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 2:07 PM

First gear, 4 wheel drive low. The lower gearing in the low range gives a lower wheel speed while still delivering adequate torque for movement. If they had an option for a 2 wheel drive and a lower gear I would take that because the vehicle wheel speed will have a smaller range for the same range of RPM. Thus it will be easier to keep the wheel speed the same as the road speed.

Drew

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#15
In reply to #14

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 7:34 PM

Think about it this way instead.

Trying to keep the wheel speed the same as the road speed by keeping the wheel speed rigidly tied to the engine speed is a losing proposition. Irregularities in the road surface may require rapid changes in wheel rotational speed to maintain contact (or at least surface to surface velocity match) with the road. Since it is very difficult to make rapid changes (increases or decreases) in engine speed, the preferred solution is to keep the clutch constantly slipping and regulating the applied torque while letting static friction keep the wheel rotational speed at the proper value.

Note that this treatment explicitly ignores the moment of inertia of the wheel/tire system and the drive train from clutch to axle. Including that should be good for an additional 40-50 posts.

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#16
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 9:28 PM

The question was about starting.

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#171
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/30/2010 9:35 PM

If you break traction the engine will rev, storing energy in the flywheel. If you store too much energy, the chance of quickly regaining traction is lost. That's where second gear looks good, because total revs and hence total flywheel energy should be lower, making it easier to momentarily "catch" traction again and soak up those revs. It's the law of small numbers working for you. But your touch on the clutch has to be pretty good to take off in a second gear that's good for 50mph flat out.

The other element is the torque curve of the engine. A sports car with a big cam and no bottom end might be fun for awhile on ice, but not if you wife's in the car with you; and the revs will runaway in first gear or it will splutter and die in second. No gear choice will work and your ear will burn too. Old diesels do the opposite, losing torque as revs rise and forgiving virtually any choice of gear you make on ice. Boring but effective. Traction control without the electronics. A bit like some marriages...

Now if your first gear is extra-low, like the crawling gear on a Hi-Lo 4WD box, you won't get runaway wheel speeds no matter how hard you rev the engine. A slightly slipping wheel still finds bits of grip as it squirms around, and at really slow speeds the runaway flywheel is not the issue. (The issue is actually the appalling gas consumption you get driving a 4WD or SUV.)

Truth is we're all saddled with the car that we bought, so I reckon a light touch on the loud pedal is probably all that counts on any sort of slippery stuff.

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#177
In reply to #171

Re: Slick Roads: Newsletter Challenge (03/02/10)

08/30/2010 12:28 AM

don't drive with stones on your feed!

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#17

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 10:38 PM

I live in the tropics but I'll attempt an answer anyway....

I would try to move off in 2nd gear. There would be less torque transferred to the drive wheels than if I were to attempt motion in 1st gear so there should be less chance of skidding - i.e. better traction. Although 1st gear and reverse gear are the most powerful starting gears, 2nd gear is still a power gear and it should be possible to move off (albeit more slowly) in that gear.

.... how's that?

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#20
In reply to #17

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 11:12 PM

In an automatic ransmission vehicle, if you have the choice of starting in a higher gear, do so. The torque converter multiplies torque and when used in first gear it is very hard to control enough torque multipliaction to prevent one wheel from spinng, and once that happens in most cars you get little to the other wheel. Limited slip transmissions are an exception to this.

If you start in second gear, the lower available torque makes it easier to avoid slippag. Limited slip or positraction helps in this case as well.

With a clutch, you need to have a little continuous slip to limit the torque, which is easier in second or high gear. experienced drivers can manage in first with precise control os slippage

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#19

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 11:11 PM

The question didn't say if the vehicle was a car, truck, FWD, RWD or AWD, with or without traction control, snow tires, studs, limited slip diff, etc. Makes a lot of difference.

I agree with Drew K: 1st gear low in an AWD truck. Even with summer tires, my Dodge Ram will go prit near anywhere in 1st Low, while it just spins the tires in 1st High.

My BMW 740 has traction control and Blizzaks, so it goes pretty good, too. Before I put the Blizzaks on to replace the Z-rated summer tires, the 740 would creepy-crawl away on a standing start as the traction control tried vainly to find some traction with those tires. But with the Blizzaks, it takes off just fine from a standing start on ice.

I once raced a Datsun 510 pro rally car with a 4:44 240Z limited slip and studded snow tires. That's pretty low gearing, but on winter rallies with snow and ice, that car would literally LEAP off the start line into a stage in first gear. The special rally studs protruded about 1/2 in from the tire, and left sparks on dry pavement.

I once made it all the way up to the Mt Tremblant ski area in my 1967 Buick Riviera durng a raging blizzard, passing nearly a hundred cars stuck on the steep hill. The RWD Riv had a limited slip and studded snow tires, and we were virtually the only car to make it up the hill. The parking lot was deserted except for some AWD vehicles, and we cut trail on a half-dozen runs that day before they got the road cleared.

Point is, we should have been told what equipment we are dealing with here before answering the question. It makes a big difference in the answer.

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#21

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 11:44 PM

Traction is the same - being the coefficient of friction. This is the answer to the question as posed.

Being "read in" - not stated - is the assumption that there is snow under the stationary cars wheels. Secondly, that snow is the cause 'slippery', not melt. Thirdly, what matters after you have started motion.

450 Ø

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#22

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/01/2010 11:50 PM

I live in Canada and drive in all kinds and combinations of ice and snow. Based on my experience with a manual transmission I use second gear, a little higher revs and slip the clutch very gently. With an automatic on ice, I just release the brake and wait while the car starts rolling. It has not mattered about front or rear drive; the main thing is to keep the applied torque low.

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#23

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:20 AM

Anonymous hero and Dave Uggla both gave excellent answers that I totally agree with. One thing I have noticed however is that no one has addressed the issue of power pulses. If you have ever driven a rotary engine you will know of what I speak. Generally speaking you will find that traditional v type and in-line engines have noticeable power impulses that will actually cause loss of traction. The opposed engines such as Subaru do not generate as much impulse and the odd number of cylinder engines such as the 5 cylinder Audi we owned also seemed smoother. The Mazda rotary engine is amazing regarding the smooth application of power. In short, with some engines I feel that the lower rpm sometimes creates bigger pulses so there may be a trade-off here when you want to lug it in 2nd gear. In the end, the smooth experienced driver is always the answer. ( along with awd and studded tires)

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#24

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:17 AM

There's an old rally trick that no one mentioned: Spin the tires like crazy to get them hot, and they will grab much better. (Works in the rain, too--which is why race cars on slick tires can go so fast in the rain, as long as their tires stay hot).

A few years ago, the local SCCA held an ice autocross on a frozen pond, so I took my clapped-out 1984 Olds 88 4-door sedan down there. It had a limited slip and snow tires. Using the hot-tire launch--and a trunkfull of bricks--I beat everything except the AWD cars--in a 5,000 lb Oldsmobile! The extra weight and the hot tires let me launch into the course much faster than anyone else, and that's what won it for me. Unfair advantage? Nahhh...anybody could have done the same.

This may also explain why a car that's spinning the tires on ice suddenly gets traction and lurches off--the tires get hot and get traction.

Hey, maybe that's the trick answer to the original question. Start in first and spin the tires until they get hot!

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#25
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 5:24 AM

No good on deep snow - you just dig yourself in

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#26

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 6:36 AM

I go along with the consensus here, 2nd gear is better to avoid spinning the wheels. I have noticed in the recent snow that my current car, which is the first I have had with traction control, can be a little difficult. The use of 2nd gear & gentle throttle still works but as soon as the car detects a little slip it cuts the throttle output which, if you are already being easy on the pedal, can stall the car.

Having said that, in the worst of our snow (which I know is nothing compared to what some of you have to cope with) I was still able to drive past others who were going nowhere fast.

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#27

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 7:44 AM

The idea is not to break traction in starting the wheels moving as the static friction coefficient is greater than the dynamic coefficent. If you have a vehicle with an engine that has clutch engagement torque (truck engine torquey enough at idle to be able to start and move the vehicle by just letting out the clutch without speeding up the engine) and a suitable gear ratio, then theoretically you could start it in first gear, easing out the clutch and staying off the footfeed. But with a conventional vehicle you would probably have more control in second gear, slipping the clutch and gradually getting it moving without breaking traction, so the short answer, is yes, you will probably have better traction control in getting it started in second gear, altho the clutch might not survive too many of those slip starts.

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#36

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 9:49 AM

I've always driven manuals and never had problems starting in first gear. Very slick or icy roads 2nd gear works well. When deep slippery snow is a problem, rocking in first allows me to get momentum to get out of the ruts. As stated many times above, practice and finesse will get you going every time. That and the 150 lbs of fill in blank in the bed of my pickup.
However, physics says 2nd gear.

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#37

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 10:36 AM

Better traction will be achieved by having 2nd gear when starting the car's motion. Using first gear will give less traction due to faster initial rotating speed of tire.

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#42
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 11:59 AM

Answer and reason appear incompatible...

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#38

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 11:08 AM

Cars and tires have evolved in the 80 years since there was any merit in starting in second gear.

Like most winter sports, this is a matter of applied physics.

A number of conditions are significant but not defined by the person who posed this question: slope, temp, depth of snow, vehicle layout, and tire design.

1. Temperature. I drove in the Great Lakes area for decades, and temp could be +3C or -25C in winter. Traction is far better when it is cold. In Manitoba, I find driving easier and more fun, as there are no really slippery roads for months at a time. (It can stay below -15C for a long time.) I have been Ice Race Director and an ice race official for more than 20 years. We learn a lot about tire traction on ice. At -25C, tires are very tolerant of a few seconds of wheelspin. They will quickly recover. If it is cold, and there is not much depth of snow on the road, there is no zero-traction issue.

2. If there is little snow, but it is nearly zero Celsius, you have the classic icy traction problem. In this specific case, you need to keep your tire tread from warming. A bit of tire slip will do this. When you have made this error, you need to let the tire and the snow under it cool to ambient. This is a good opportunity to get out the shovel for 5+ minutes. You avoid this warming by minimizing slip. This is easiest in a manual trans in the lowest gear, with a keen ear for engine speed. Learning the normal effect of applying power with the clutch is good too. If you apply power for half a second, and the vehicle does not move as expected, you have slip, and must back off. If you can release the clutch and cut the throttle in the first half revolution of 'slip' of a driven tire, you are skilled enough for this job. If the tire may spin for 20+ seconds before you take corrective action, you may be in that spot for longer than you intended. With freshly warmed (spun) tires, each sitting in a wet, icy little trough, tire traction will be no more than a twentieth what it was before you spun your tires. In bad conditions, applying enough torque to move the car is usually enough torque to spin a tire. Simply using a higher gear is not enough. In second gear, one still has to be careful not to spin a tire. If the vehicle is moving, the critical tire moves onto 'fresh' snow or ice as it slips. In this case, up to 30% slip, at -6C or lower, will not warm the tire much. Creeping along in the lowest gear, with a light touch of the throttle is best when you have begun to move. In a higher gear, you cannot maintain this 'under 30% slip' situation.

3. If there is deep snow, you have enough resistance to vehicle movement that you need to employ vehicle momentum, for at least the first meter of travel. For this to work, you need to move forward and backward, hopefully with the front wheels nearly straight. You need to use your shovel to make sure the vehicle's weight is all on the tires, and to minimize the depth of snow they must chew through. If the floorpan rests on snow, you have an impediment you do not need. A useful technique is to 'bump' the clutch for a split second of engagement, followed by a couple of seconds of no power. When you adjust the frequency of such power applications to the natural frequency of the car's inclination to rock forward and back in its little patch of flattened snow, you can often get underway without even using reverse gear. Getting this right is more fun than winning at Scrabble, but certainly not any easier.

4. Tire choice is more important than engine-over-drive-wheels. Of modern front-drive cars, only very light ones have much front weight bias. A 3800+ pound front-drive van will not have much front weight bias, and will have little advantage over a rear-drive van. If lawful, carbide studs will help on 32F ice. Deep tread and lo-temp rubber compounds are good in winter. A tire design that does not retain snow in its tread grooves (a pure snow tire) is an important factor. I have been using 25cm by 120 cm scraps of expanded metal lath (slits in 5 to 8mm steel plate, expanded into diamond shaped openings, making a very high traction steel surface) and a shovel, as needed, for more than 40 years. These have always got me out of what bad driving choices got me into.

If your car is an automatic and so silent that you cannot detect early-stage wheel spin, you may be doomed.

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#41
In reply to #38

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 11:55 AM

You don't seem too supportive of my "hot tires" trick for launching into a rally stage or an ice autocross. Seems to me that it worked very well--especially with the big Olds on the icy pond. I picked up the trick from one of the old how-to-rally manuals, writ in the 1970s.

Or maybe it was my imagination, clouded after all these years. Could it be the changing nature of the tires? After all, in my rally days, we ran on bias-ply tires.

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#43
In reply to #41

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:04 PM

The best method depends on the depth of the snow. If it's really shallow, hot tires will help. Otherwise, best keep 'em cold as possible.
(No, not with window deicer, as that raises the melting point of the snow)

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#44
In reply to #43

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:18 PM

OK, so launching into an ice autocross from an ice surface works with hot tires, but it doesn't work when launching from snow. Got it. Whew! You had me doubting my memory for a while there. Thanks.

I always hated winter rallies, even though I did reasonably well. Once, we we got up to fourth on the road at the 20 Stages Rally in Michigan, with my lil ol stock-engine 510 in amongst the fire-breathing million-dollar factory works cars, like Escorts, Porsches and Wagoneers. Alas, I suffered the same malady that puts many cars into snowdrifts in the forests or upside down in the median of an interstate highway--brain fade--and finshed 10th. I guess, of all the problems we've talked about on this thread, brain fade is the worst.

*sigh* Nostalgia just isn't what it used to be.

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#45
In reply to #44

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:30 PM

No prob. But I'm more into amnesia (like not remembering my pulse rate the time I rotated my car 450O on an unexpected black-ice corner and drove on without stopping).

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#49
In reply to #45

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:58 PM

Amnesia fer sure! That would be a 360, not a 450. Unless you drove on in reverse.

Actually, pulling a 360 is an old rally trick to stop a car when the brakes fail. It has something to do with converting forward momentum into angular momentum, and it takes real skill to spin a car on a one-lane forest road. I never mastered that one. But I bet your car slowed down considerably when it happened to you.

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#52
In reply to #49

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:16 PM

As I remember it was a 90O bend, and I went round the corner, spun, and righted myself after a full extra turn. 360+90. It was black ice - lucky for me the car just happened to be going along the new direction as it finally lost grip. And yes, I had slowed down to about half the original speed (I think - hard to be certain when your metaphorical underpants are in the state mine were). But overcoming this amnesia is getting dangerously like therapy - I could become dependent.

By the way, I have my doubts that it's the conversion of momentum to angular that does the job. I would have thought that spinning the car was a way to place the wheel rotation orthogonal to the road - and presumably continued rotation of the wheels gives the tires some chance of cooling off.

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#54
In reply to #52

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:48 PM

Black ice is the worst condition of all. As I recall, it results from melting during the day, freezing at night, and it builds up over several days of thawing and freezing. Put a fresh coat of snow over it, and it is more slippery than a politician's PR staff.

When we ran winter rallies, it was mostly through Michigan, Ohio and New York forests, on snowy roads with anywhere from a few inches to two feet of snow covering the dirt, sand and gravel roads. Once, we popped up out of the forest onto a closed-off paved state highway in Michigan. The road led to a fishing camp, but Michigan closed it in the winter, so it was never plowed. The stage was called "Flying Volvo," and when we ran it, it was covered with black ice.

Driving such a road at 100 mph requires teeny-tiny steering wheel movements measured in micro-degrees, looking for snow at the side of the road to keep a wheel in, and NO SLIDING! You slide, you are off the road! When we flashed through the finish control and braked, the car slid a hundred yards before it finally stopped.

My lil 510 was only capable of 100mph, and we got there twice on rallies--once was on Flying Volvo.

But that brings up another winter driving trick--when faced with an icy surface on the road, keep two wheels in snow at the side of the road. There's more traction there than on ice.

Hey, this is a fun thread! Haven't thought of this stuff in YEARS!

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#46
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:39 PM

I still have a souvenir from the 70s, a (road-race modified, bright yellow) 1969 510. Its 'engine not over drive wheels' design gave us all a huge disadvantage in the 70s. 1950s Porsches had great initial traction for winter rallies, but could hide away 1000+ pounds of ice, packed into those 4 huge wheel wells. Not so peppy then, with 3500 pounds and only 80 hp.

As with most things in life, there is merit to learning and experimentation. Learn then try. Getting underway on ice or a plowed road is very different from those situations, from which you may need help to escape. My letter above may seem long, but still only touches on the main points of this complicated physics exercise.

In the case of the quiet, auto-trans vehicle, with an unpracticed driver, using a higher gear makes limited-torque launches easier. A 5 speed Sprint, with snows and an experienced and careful driver, is better started in low gear.

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#51
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:04 PM

Loved my '72 510! It was the most reliable, bulletproof car I ever owned, even though we completely thrashed it on pro rallies. No wonder that 75% of every starting grid for a pro rally in the 1970s was a Datsun 510. They never broke, never failed. We called it the "poor man's BMW" because it had everything a 2002 had: Macpherson struts, independent rear suspension and OHC engine. We put a 240Z limited slip and African Safari suspension in ours, and had a ball. Good to hear from another 510 fan!

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#63
In reply to #51

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 4:02 PM

SEEKING SNOW ON ICE

In the early 90s, I twice drove north, leaving Dallas on New Year's Day. Both times there was a huge swath of freezing rain. The day before there had been a traction issue in Dallas. They had sanded, but a day's traffic had blown that sand onto the 'grease-stripe' and along the dotted lines. The well-used parts of the road were devoid of sand. Every overpass (there are many) on I-35 had at least one car overturned or slid into the distance. For us it was simple: drive with at least one set of tires on the line of sand.

Hours later, we drove north through Kansas, with over an inch of hockey-quality ice over the whole freeway. I had slowed to about 50 mph. I overtook a state trooper. I was keeping my left tires on the shoulder where there was a wisp of snow. (I did not have studs on at the time.) The trooper called out on his loudspeaker system, suggesting that I slow down, as he crept along in the slow lane, at perhaps 15 mph. Under these conditions, anything crunchy is your friend. Once you learn where to find traction, and what sort of things will happen when that traction disappears, you can go a long way without ever 'sitting on the sidelines' so to speak.

Nothing like a light, low car on carbide studs for really icy roads. When it gets to -35C or colder, the ice hardens so much that the studded advantage is diminished. By that point, plain rubber works very well, and street-studs carry 80% of the vehicle weight on rubber not carbide anyway. Flat-top Euro race studs have very little traction at -35, and carry all the vehicle weight, but they give you >0.7 G cornering and braking, in warmer weather on shiny ice.

As far as heat softening rubber, modern winter-tire rubber is pretty soft at any ambient temp, in its first few years of life. Even 5 year old snows are pretty soft in the cold, nowadays. A +10C tire in -20C snow might have an advantage, but I have not tried it. We know that a set of +25C slick road racing tires on a +5C day are much stickier than cold ones. Melting the underlying snow is the bane of those stuck. Everyone who is stuck long enough to get on the national TV news, seems to use the tried and true "hit the gas and spin them until the cows come home' technique. It garners viewer sympathy, but does not get you on your way faster than 'minimal wheelspin' techniques.

My 510 is the last of many. I gave my sister the 247th one made, from August 1967. Too bad it is now gone. My 1969 has 240 Z rear aluminum drums, 280ZX vented rotors and a later 5 speed. As a race car, it has no undercoating or interior. Every occupant can hear clearly each 3 mm piece of gravel that gets flung up by a tire as it ricochets underneath. It is very light, even with the steel rollcage. The 510, early 911, and TR4A IRS all shared the same rear suspension geometry. My TR4 and 510s got to use the same rims at times! There is nothing like a front engine, rear wheel drive, like a 510, on all-season tires to teach you how to find traction on a warm winter's day.

I am sure each of us old guys has amusing tales of winter driving and traction.

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#58
In reply to #43

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 2:38 PM

Doesn't melting ice on the surface make it slippery, so wouldn't warm tires make ice wet and slick?

Isn't that how ice skates and snow skis work? Same would go for raising the melting point, unless you can melt through to pavement, it seems to me that warmth or deicer will just make it slick.

Drew

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#59
In reply to #58

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 2:52 PM

No, it has nothing to do with melting the ice. It's just that tires have more traction when they are hot, because the rubber is more pliable and has more grip...I think. I'm still not sure why this applies to ice but not snow, but I yield to the superior knowledge of our ice racing expert.

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#61
In reply to #58

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 3:29 PM

If the ice is thin enough the warm tires can melt it completely, and allow the tread to grip against the road surface proper. It's only useful for a short time starting or at lowish speed, as it is not possible to maintain a high enough tire temperature to melt all the way through new ice when moving at speed. Obviously the efficacy depends on the ground temperature, the ice thinness, and the thermal conductivity of the material under the ice; it's not so hot (!) on a temporary aluminum bridge, for example.

A related effect with a different cause is walking on the points of your ice skates. The point can sink further into the ice than the skate before it cools down enough to prevent the ice melting. This either allows you to grip against the substrata or provides a significant non-melting and angled ice surface to push against

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#64
In reply to #61

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 4:49 PM

A revised thought: S_O_P does have a point about making warm-weather tires more flexible - the warmth also helps to clean out the treads. This can be useful on thick snow, provided that the heat is not sufficient to melt too much of the pack; but you need the pack to be loose enough so that what water you generate drains away, but tight enough to hold together. How you achieve the heating at the start line without upsetting the stewards beats me... (Reduced tire pressure also helps - but watch out for other undesired consequences)

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#39

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 11:41 AM

Second gear. You want to reduce the application of the engine's available torque to the tires to avoid too much transfer of energy which would more readily result in slippage of the wheels on the snow or ice. You will have to slip the clutch more to avoid stalling the engine but this is much more appealing than having to beg some passer by for a push.

George Lupieri

Trail, British Columbia Canada

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#47

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:47 PM

I'm getting Guest confustion. Hard to tell who is Guest #1, Guest #2, . . . or are you all the same? Join the fun and register. We don't usually hold grudges.

Cheers !!

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#48
In reply to #47

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 12:56 PM

Of course we are all the same. Especially when we disagree or say things that are impossible.

Fyz

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#50

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:01 PM

the hero answer is great, but this has nothing to do with living in the northeast. we get snow in colorado too.

i would add that in an "all things equal" situation, that is, extraordinarily slippery, flat unobstructed surface, you can often get the car moving just a bit in 2nd, a few miles an hour, and then switch into first once you have static friction established with the car moving. that way you will not lug once you let off the clutch. certainly if you have a very fine touch with accelerator and clutch you can probably get going in 1st - sometimes by not even using the accelerator, just idle throttle - but i think the point of the question is, what's easier. and, for most people, it will be easier not to overdo the torque in a higher gear, but, as people have pointed out, that can put a lt of stress on the drive train.

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#56

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 1:53 PM

Leave the two wheel drive stuff to the un-enlightened.....four wheel drive knows no need for first or second or torque reduction....bla bla bla..just stand on it and feel the drift

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#57

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 2:29 PM

2nd gear. At least it worked in the upper mid-west.

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#65

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 5:07 PM

Hi Second gear is how we do that in the mountains

And even better with people standing on the rear bumper of the Beatle - then you

went uphill like a tank.

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#66

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/02/2010 8:19 PM

Low gear!

I am assuming that few, if any, of you use anything other than low gear to move the vehicle from a stop. There is seldom any reason to use low gear from a stop on level pavement.

Using low gear gives the driver more control.

The weakest point in the system is the friction between the drive wheel and the snow. The vehicle mass has to be forced to move and if I remember correctly the formula is f=(m)(a). You have no control over the mass so acceleration is what has to be controlled and it can be done with the clutch. You are more familiar with using low gear and have a better feel for it and you have less to worry about stalling the engine in low gear. You need only to control the clutch.

Once you are rolling, the force in f=(m)(v) working in your favor.

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#68

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 1:09 AM

Starting in a higher gear will transfer less initial torque to the driving wheels which gets you moving. However, once in motion, stopping, steering, just controlling the vehicle won't change. Slowing is done with the car in neutral so that braking is done with all wheels not with compression on the driving wheels.

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#69
In reply to #68

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 2:21 AM

You don't REALLY put your car in neutral to slow down, do you? Never heard of such a thing. If so, I want to be way ahead of you on a snowy road, not behind.

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#71
In reply to #69

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 8:12 AM

It makes sense, I used to so it in my old automatic volvo. It was easy because the floor shifter would click in and out of neutral easy.

It makes sense because even when you are off the gas, the automatic transmission is putting torque to the wheels. Recently I saw a small pickup sitting at a traffic light stopped but the left rear wheel was spinning. Either the driver was lightly on the brakes and the more powerful front brakes were keeping him still and had better traction than the back or he had problems in his rear drum brakes that did not apply enough force to keep the wheel from spinning.

I would not recommend this for most column shifter automatics because if you push too far it will go past neutral and into reverse creating either a mess for your mechanic or the tow truck driver pulling you out of the ditch your reversing wheels sent you into.

Drew

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#72
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Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 8:40 AM

Putting it in neutral doesn't make a bit of sense. The only possible situation where rear drag might upset a RWD car would be a downshift into a lower gear and having the rears lock up.

If it's an automatic, downshifts are gentle, so that won't happen. If it's a stick, just push the clutch in and keep it there.

Putting it in neutral whilst braking takes away one important aspect of car control--the ability to accelerate when needed.

If a Canadian or Scandavian driver agreed with you, I might concede the point. Are you Canadian, eh?

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#73
In reply to #72

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 10:12 AM

Some modern engines put no fuel into the engine and close the valves with minimal air content when our foot is off the accelerator. With these engines there is very little engine braking. So you should be in the optimum gear for smooth pick-up.

At the other extreme we have some diesel engines that are designed for high torque. With these engines you should be in a gear that provides minimal engine braking, but allows smooth and decent pick-up.

This applies to handshifted vehicles, irrespective of whether they are front or rear drive

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#78
In reply to #72

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 2:28 PM

I am not only speaking of the drag of engine braking. If you are being delicate on the brakes and like the pickup I saw, your front brakes will use available grip to slow you down, but may lock up on slick spots while the rear brakes are not sufficient to counter the torque of the engine at idle. I recall a comercial about a Ram pickup that bragged it could pull a max vehicle load at idle with no throttle.

That is where putting it in neutral could be a problem.

Drew

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#80
In reply to #78

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 4:40 PM

Brits are taught to disengage the clutch if the engine is counteracting your braking effort.

I suppose Americans are mainly expected to drive automatics?

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#81
In reply to #80

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 5:02 PM

Driver training in Yurp is vastly different than here in 'merica. You folks regard driving as a privilege, you teach your students how to DRIVE under assorted conditions, and--in some places, like France--driver education costs a bloody fortune.

Here, we teach students how to PARK, and driving is considered to be a RIGHT. Any idiot who can parallel park can get a driver's license in America.

I took both my kids to driver's schools. I took my daughter to a two-day course by the Porsche club, where she learned high-speed driving on a race track (Heartland Park, in Kansas) from a lady race driver.

I took my son to a similar two-day BMW driving school at Road America in Wisconsin.

Both are now superb drivers, without accidents.

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#84
In reply to #81

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/03/2010 6:13 PM

Your children clearly have other attributes; for example, many young men (however suitably taught and generally aware etc.) suffer problems with intermittent concentration, which can lead to accidents (albeit only very minor ones if they are self-aware as well).

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#93
In reply to #78

Re: Slick Roads: Newsletter Challenge (03/02/10)

03/04/2010 11:29 AM

This string is going a bit off topic, but I felt like adding 2 further data points.

Braking in neutral with an auto box: For 2 years now, our Government insurance monopoly has been running ads telling all of us to shift into neutral when braking, especially in snowy weather.

When murrican drivers had audis run away on them, and pushed on the (skinny?!) brake (!??) pedal so hard they had leg injuries and the car did not stop, one of the NHRA stars did a demo. 1400 hp drag car with brakes on hard, and lots of throttle. Car just sat there, NOT moving. There is no Toyota made that makes more torque than its brakes can retard. Of course you can wear them out over many miles of near full throttle highway use, then you have only steel on iron, but when they are cool and fresh, they can stop any 300+ hp car in seconds.

All wheel drive is not the final answer: locking all the diffs and using the best tires have benefits too. Get a new 911 GT3 with K.E.R.S. driving its front wheels. Lim slip on the rears, and an electic motor on each front wheel. Put on some nice snows.

David

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