High-tech ways to avoid speed traps

There is a better way - save gas too - slow down!

Do you actually save gas when you slow down?

Depends on gear ratio to engine RPM and drag plus required power. You will find sweet spots in the torque curve that get you better mileage.

One sweet spot in my pickup is at 27 MPH on level ground in third gear. Idle propels the vehicle almost to well (neighborhood is 25 MPH). Taking you foot off the accelerator does not slow you down.

Of course grade up or down and wind can change the speed, increase or negate the difference.

Also above 70 MPH the viscosity of the air causes more drag so unless the vehicle has a very low drag coefficient you will burn more fuel with more speed regardless.

Brad

But as you go faster you also cover more ground. In the end it's mpg that counts and that's not the same thing as burning more gas as higher speeds--right?

Yes and no, to accelerate in half the time you have to square the power applied. And the drag is not a linear function once turbulence starts.

Ride a motorcycle with no faring or wind screen and after seventy miles per hour the drag on your body is very noticeable.

Most engines have peeks in the torque curve vs. fuel flow, that running the engine at the right RPM will give you better MPG.

Drag reaches a point where more fuel is needed to produce torque to maintain speed to offset the drag. Higher gears can produce better MPG to a point but more power is needed to overcome turbulence and to be able to accelerate faster than a snail.

At higher speeds the drag coefficient is a major factor, that is why the contraptions trying to set speed records don't look like your car.

At very low speeds your car is waisting energy vs distance traveled (worse than normal) then it approaches optimum at certain points of gearing verses fuel use until drag overcomes efficiency.

Race cars need to be able to change gearing and torque vs speed to adapt to different tracks and MPG is very important because pit stops take time.

Variable intake runners, valve timing and transmissions on piston engines to change the torque and horse power curves has been a subject of interest of many a gearhead.

Thanks you just created the conditions for a new variable transmission using eddy current drive. No reason I can think of at this time for it not to work.

Brad

The miles per gallon is directly inverse to the speed of your car.

In a perfect world, yes but ICEs are not perfect. They are designed for specific use, and the broader the power band the closer it is directly inverse. Automatic transmissions help widen the power band also. At the extreme many 18 wheelers have a very narrow power band an lots of gears to be able to use it.

Until locking automatic transmissions a standard transmission could be geared to have better MPG in the same vehicle. Now there is not much difference. I put a 6BB1 Isuzu in a Ford 1 ton pickup. To go 55MPH in overdrive you had to speed up to 61mph to shift into overdrive then idle back down to 55 where it got 25 MPG. It didn't care if it was loaded or not with oil barrels. It only dyno ed at 175HP at the rear wheels but the torque would break lose the tires in the first three gears.

I have been looking for another 6bb1 to play with.

Brad

That's incorrect. A car that is doing 0mph and that has an engine running is achieving an instantaneous 0mpg, like my house <cough>.

True you have to have a gear first to put it in gear.

But a car at terminal velocity with the engine off gets infinite gas mileage but has an ultimate break failure. Those sudden stops are a b%^&h!

Brad

Brad is right but the sweet spots is found at different speeds for different cars.

My current cars are definitely lighter when going slower.

I however had a Citroen ID 19 in ±1965 which was lighter at 85-95 MPH. (that was in any case what I wanted to believe).

This is all interesting but, not being a math major, I'm having trouble comprehending it all. What's an 'eddy current', or maybe I should say what does it have to do with a transmission design (I live near an ocean)? Also, how does one find the sweet spot for a particular vehicle? Is there a magic formula?

1. Eddy current is described here. I don't see how it applies in the context of this thread. [Edit: Think Brad was doing a bit of off-the-wall thinking there (whatever that means )]

2. Unfortunately, there's no magic formula for the 'sweet spot' for cars - it can only be found empirically (i.e. by lots of tests at various speeds & with varying road conditions etc.).

I'm glad you asked goosemydog,

An eddy current drive is a variable transmission on an electric motor.

http://www.netaworld.org/files/ItemFileA875.pdf

http://en.wikipedia.org/wiki/Adjustable-speed_drive

They are used on everything from high end wood lathes to Nuclear subs.

Might just be away to replace the transmission with an eddy current device for full range sweet spot. There is a bunch of new material tech for magnets and eddy current matrix. Also add a magnetic locking device for 1:1 output at speed.

As for transmission losses, measured engine HP minus measured rear wheel HP. They are far from perfect.

Brad

OK, since we're going unscientific, this story might apply. Years ago I knew a guy who rebuilt carburetors for a living. He always had a vacuum gauge in his vehicles. He said the lower the vacuum, the higher the mileage.

When the vacuum is low, the carburettor isn't sucking in much fuel. If it isn't sucking in much fuel, it isn't burning much. If it isn't burning much, then it isn't working hard, so it is going to be more economical - a very important consideration with petrol rationing.

On my commute to work I notice that most drivers (myself included, I will admit) are travelling at a speed of about 75 MPH. According to published reports, a reduction in speed from 75 to 55 will result in an average mileage improvement of 10 to 20 %. At $4/gallon this is equivalent to a $.40 to $.80 reduction in the price of gas. I don't see many people slowing down, so I have to conclude that few of us are really very concerned about our fuel costs. We love to complain, but gas prices are not so high that most of us are willing to adjust our behavior.

As to the reasons for the inverse relationship between speed and mileage, remember Relativity. The faster we go, the more massive we become! It takes a lot of fuel to push us speeding heavies around! (Before replying please note that my tongue is inserted firmly in cheek.)

Bill Morrow

I don't have any trouble with speed traps.

Here is a picture of my Transport:

That's what we are going back to, unless Solar Cells and electric wheeled cars become cheap enough for all.

Kind Regards....

Hey Sparkstation,

My Grandfather still farmed with horses while I was growing up and my parents and other family raised mustangs for a hobby till just a few years ago. The last time I got to work with the horses we had 50 colts that year.

The problem now days is the horses are smarter about travel than most of the riders.

Brad