high gas prices,high air pressured tyres

Seems like you are talking about an almost total redesign of the car. Not economically viable. Most cars could stand to have better control of their air pressure, however. I generally keep my 35# tires at 40# and keep an eye on the tread wear. They never have but should they wear more in the middle, I would reduce the pressure. Keeping the proper alignment is also important. A great deal of gasoline is used pushing underinflated, poorly aligned tires down the road. Brake calipers running too tight are a real drag also.

I say this as a 30 year brake and alignment specialist.

It's always a trade off between low rolling resistance and good grip/handling.

If you set the steering up parallel with small dia high pressure tyres, you'll get high milage but a twitch car that doesn't handle.

Del

Better gas mileage? Easy-pave all roads with asphalt instead of concrete! Asphalt has less rolling resistance than concrete, thats been proven. James

May depend on the tread pattern, my concrete wheels roll very easily except uphill and over hot asphalt!

Hello:

When gas hit $2.00 a gallon, I started to run my tires my tires at a higher pressures.

What is the the best way tp- save gas. If you buy a good quality tires, that provides a good ride at higher pressures, are there good gas savings to be had? What about rotating them more often? Should you run all four tires the same pressure (front and back)? What about going to low rolling resistance tires?

I would really like to know.

I have always run my car tyres at the maximum load pressures set by the car manufacturer for when fully loaded up, all the time.

Through this simple trick I get good gas (Diesel mileage) and also exceptional "Tyre" Mileage!!! 100,000 or more miles are not unusual for me on many different cars over the years.

Buy Michelin is also a good idea as they actually try to improve mileage also at the normal pressures too....

Back side is a "Hard" springing that actually you get used to after a day or two.

Braking is actually supposed to be better as, as well as steering is more direct, I like these two effects completely.

Not "Tailgating" is much safer and allows you to drive better with less use of the brakes, so less brake AND tyre wear is a good result to have!!!

If someone follows me too closely, I add the missing meters between us to my distance to the next car ahead, this allows me to brake slower and their is less chance that I will get r(e)ammed in an emergency situation!!

The books tell you that the tyres will wear first in the middle if run with higher pressures. I have NEVER ever seen this effect, it probably only happens if you run with double the normal pressures.....or more!!

I recently drove back from Italy, with a 140 BHP Diesel engine and towing a 1.5 metric ton trailer (caravan) and averaged well over 30MPG (9 Liters per 100 Kilometers).....sometimes it even dropped (the daily average!) to less than 9 Liters.....

I averaged 76 KM/Hour for the whole time I was driving, that is I drove mostly around 90-95 KMH, which is not slow, nor is it strictly legal either!!! Slower (legal speed!) would have given me an even better consumption!!

This is a very good idea, provided you are not unhappy with the handling characteristics of the new tires.

Replacement tires range in coefficient of rolling resistance (Crr) from about .006 to .013 (when inflated to recommended pressures). I happen to have a spreadsheet for calculating the effect of such things. If I cruise on a perfectly flat road at 70 mph in my Accord, with tires rated .013, then I get (a calculated) 35.3 mpg, with 18 hp required to overcome aero drag, and 9.7 hp required to overcome rolling resistance. (I recently did a 400 mile trip at speeds over 70 and got 34.25 mpg overall, so the calculated figure is pretty close.) If I use low rolling resistance tires, rated .006, then aero drag remains the same, but only 4.48 hp is required to overcome rolling resistance. The fuel efficiency goes to 43.5, if I assume the same engine efficiency at 27.7 hp and 22.5. This assumption is not correct, with efficiency (measured in lb/hp/hr) being lower at the lower hp. But 41 mpg would be a reasonable estimate, I'd think. That is a very large difference for replacing tires -- particularly if your old tires are already worn out (as those on my Honda happen to be), so there is little additional cost for getting the low Crr tires. (The original tires on my Honda are already reasonably low Crr, so my percentage difference will not be this large.)

The Bridgestone B381 (the lowest resistance tire) is only available in the size used on the Honda Insight, if I recall. But many of the the others in the Wikipedia article list are available in a wide range of sizes. If you Google for low rolling resistance tires, you can find other lists, too.

Many people do not like the "feel" of low rr tires, and it is worth considering the wear and traction ratings too (which are printed on the sidewall). But my new tires will definitely be the lowest Crr I can find in my size.

I really have never noticed any negative handling differences with running at the highest recommended presures.....only positive ones.

That is on many, many cars over the last 35 years or so..........

I am sure that if I went substantially OVER the recommended figure, then bad handling characteristics could possible occur.....I have absolutely no idea (and no thought to try either) as to when that might occur....

Oh BTW, I always run in new tyres fully before inflating them to the highest possible legal pressures, usually around 1000Km or so.....sometimes less, depending upon when I need to take a heavy load, but usually at least 500Km....

I really have never noticed any negative handling differences with running at the highest recommended presures.....only positive ones.

I think that is generally true, although a pyrometer might show that lower pressure is better for ultimate grip. In oval track racing, each tire has its own ideal pressure, based on pyrometer studies.

The objections people have re low rr tires have to do more with the tire construction and compound rather than with air pressure. Many low rr tires just aren't very sticky. But subjectively "handling" is about more than ultimate grip with some people preferring the characteristics of low performance tires over high performance ones, and vice versa.

Such statistics and methods are for people racing around circuits and changing the tyres every 100 racing miles or even less.

The tyre design and softness is also quite different to normal road tyres. The analogy is interesting but not helpful in any way.....

This "racing" info has next to nothing to do with normal driving on normal roads with tyre changes being made only when required by law or when rain causes the tyre to leave the surface and aquaplane.

Even if a pyrometer showed me that on a particular day, with a particular road temperature and a particular air temperature a specific tyre pressure worked best, this is basically useless (even if somewhat interesting to a scientific mind like mine) information. I am not going to readjust my tyre pressures 3 or more times a day!!!!!

I set up my tyres for the best feel in handling over a wide temperature and load range.......most people do not even go that far and use the basic pressures for all things, including heavily loaded going on holiday and wonder why a tyre bursts!!!! That has never happened to me except once in a hire car......in the late '60s....I did not like the experience either....

When tyres start to Aquaplane, that is the point when I personally change them for new. The laws here allow for running with only 1.6 mm, but that is far too low a profile for safety for me!!! Generally, I find that I need tyre replacement with around 3mm of tread, depending upon tyre type, car weight etc etc etc....

Such statistics and methods are for people racing around circuits and changing the tyres every 100 racing miles or even less.

On the contrary, ordinary automotive engineering or re-engineering (which is what the original poster is contemplating) includes measuring temperatures across the width of the tread to determine optimum pressures. Most passenger car tires are rated at either 35, 44 or 51 psi maximum inflation pressure. Even in the same model an in almost the same sizes, the maximum pressure rating may be different. It is very rare that an automobile manufacturer recommends that the tires be inflated to the maximum (sidewall spec) pressure, even if the car is loaded to its GVWR. Clearly, the car manufacturer does not simply guess, or pick a number out of a hat. Instead they are very likely to pick a pressure that equalizes temperatures across the full tread width.

I was not suggesting that every car owner go out and buy a pyrometer, but that there is indeed an ideal pressure for a tire based on the desired handling characteristics, and that this ideal pressure is often best found by using a pyrometer. Thus if you want to set your car up for autocross, using street tires, the recommended method is to pick the pressure that produces even temperatures across the tread width (too low a pressure and the shoulders work too hard, too high a pressure and the tread center works too hard).

The tyre design and softness is also quite different to normal road tyres. The analogy is interesting but not helpful in any way.....

Both tire engineers and automobile engineers find pyrometers quite helpful when working with ordinary passenger car tires.

I set up my tyres for the best feel in handling over a wide temperature and load range.......most people do not even go that far and use the basic pressures for all things,

Before, you said that you "have always run my car tyres at the maximum load pressures set by the car manufacturer for when fully loaded up, all the time." Perhaps that provides the best feel in handling for you, but for many people it would not. Many people will change the front/rear pressure ratio in the interests of desired handling characteristics, or will set overall pressures in concert with the manufactures recommendation, typically using lower pressure for lower loads, higher pressures for higher loads. For older, rear-engined VW's and Corvairs, running with excessive pressure in the front tires could cause dangerous handling traits: better to follow the manufacturer's recommendations.

Of course, then there are vehicles like the Ford explorer, for which only 25 psi was recommended by Ford. This is a case where marketing rules over engineering (but engineering lacks the chutzpa to say "wait, we shouldn't do this!")

Personally, I have never even met anyone with a Pyrometer, though its use is blatantly obvious. I have never ever even seen one in a Tyre shop either.....

If we all needed one, then why was it not recommended and maybe supplied with each car?

Its all very well to theorize and of course tyre and car designers need such equipment, but not a tyre shop it would seem, nor of course even any normal Joe off the street.

What you wrote is simply for 99.9999% of the driving population is simply OTT.....if it was needed, the German Law would require one, and it doesn't!!

I personally ONLY use the maximum recommended pressure by the car manufacturer , (maybe you did not read my post saying that) as this has already been tested (probably using a Pyrometer or most likely today, an infra red camera system!) for that model of car and tyre size.

In all the car manuals I have seen, there is only different pressures shown for different loads. I have NEVER EVER SEEN different tyre pressures for winter or summer, tropics or North pole........so it would appear that the GREAT majority of the people involved in car and Tyre production for road vehicles do NOT see a need for such accuracy that you seem to follow for yourself.....I wonder why???

By the way, in most of Europe that I know of (maybe not all!), you only have certain tyre/wheel combinations that are set by law for each model of car, there is not the dangerous "freedom of choice" that the US market appears to have in this area.....

If you want something different, you have to get the TÜV to test and agree to it (and get it entered into the car's paperwork), otherwise it is simply not allowed....

The Police also have the right to spot checks on the roadside, weigh your car and measure tyre pressures. I have not ever heard of this being done in the USA!!!! The fines here are not good for being overladen or over pressure!!!!

So I do feel that such gadgets as the Pyrometer are totally wasted in a European environment for anyone with even just a modicum of Common sense, who follows the law, such as myself.

But there might be a case for them (if I understand you correctly) for the USA, but as legal road speeds are so slow there, I could be wrong.....I personally feel that they are probably only good/needed for the racetrack as someone else pointed out earlier......and design engineers such as your good self. But I do feel that you are visibly overreacting with regard to the rest of the known world....

I suppose you are being deliberately obtuse, or are simply reacting without reading.

For instance, you say, If we all needed one, then why was it not recommended and maybe supplied with each car?

But I had just written: I was not suggesting that every car owner go out and buy a pyrometer, but that there is indeed an ideal pressure for a tire based on the desired handling characteristics, and that this ideal pressure is often best found by using a pyrometer. Engineers do indeed use such tools to establish recommended tire pressures, for full load vs light load. If one is going to re-engineer the car, (playing engineer) by changing tire pressures to something outside the manufacturers recommendation, (such as by running the car lightly loaded with the tires inflated to the full load pressures) then perhaps he should have the tools of an engineer.

The original poster is talking about re-engineering the car, and refers to changes in suspension (and possibly even seats) being potentially required. He was not asking the idiotically simple question "would I get better mileage if I inflate my tires to a higher pressure?" Here in the US, you can scarcely go for more than a day without someone telling you to keep your tires properly inflated -- it's in every list of "things you can do to get better mileage". There are loads of people who overinflate their tires to the maximum printed on the sidewall (or beyond) in the interests of better mileage. The original poster was asking, I think, about a more reasoned approach, particularly as he acknowledges the redesign of suspension required.

Given that this is an engineering forum, it is reasonable to assume that the original poster might want a more complete answer than simply, "Andy says he inflates his tires to the figure for a fully loaded vehicle even when the vehicle in not fully loaded." Clearly he was asking about a different type of tire (high air pressure tires, as used on trucks and buses) rather than simply asking about how much air to put in his existing tires. If we are simply making suggestions about how much air to put in a production vehicle's tires then our recommendation must be: "Inflate to the vehicle manufacturer's recommendation, according to load." We should not be recommending overinflation, (such as running the tires at full load pressure when the vehicle is lightly loaded) because we are then recommending that the owner not follow the vehicle manufacturer's guidelines.

My point in bring up a pyrometer is that this is the tool with which you can see how hard the center and side of the tread is working, and is the best and most commonly used tool for engineering and re-engineering tire pressures. Here, in the US, every enthusiast has seen pyrometers in use in NASCAR. If getting good handling was simply a matter of blowing up the tires harder, then the racers would not be so obsessive about the temperature distribution across the tread. There are hundreds of articles on the web about using pyrometers, and all agree that if the tire is hotter in the middle of the tread than at the shoulders then the tire is overinflated, and that therefore the shoulders are being underutilized. This applies to both street and racing tires.

Obviously, there is no need for Joe Blow to have a pyrometer, nor is there a reason for an ordinary tire shop to have one. But if an engineer in an engineering forum says that one should ignore what the real engineers say (who do use pyrometers to establish recommended pressures at various loads) and simply overinflate tires all the time, then that person should supply some hard data to support that contention. Such hard data would need to be something more than your own subjective view that the greater the pressure, the better the handling (I really have never noticed any negative handling differences with running at the highest recommended presures.....only positive ones.) As I replied, this is generally true, but there are many cars in which too high a pressure for the load makes the handling both less pleasant and more dangerous: original VW beetles being a good example in which the handling becomes relatively more unsafe if the tires are inflated to the full load recommendation and the car is then driven with a light load. The reason for this is that the front/rear weight distribution changes with load, and the ratio of pressures that works well for one load does not work well for another. Ordinary enthusiasts, driving cars like Porsches, are often nearly obsessive about tire pressure f/r differential, because it can have a significant and noticeable effect on handling, even when driving on public roads.

In practice, there are not "high pressure/low rolling resistance" and "low pressure/high rolling resistance" tires for passenger cars: in other words, there is not a clear correlation between maximum (sidewall placarded) inflation pressure and rolling resistance. Thus there are 35 psi tires with lower rolling resistance than 51 psi tires that fit the same car. So my point, early on, regarding the meaningful differences in tires from an engineering standpoint remains valid, namely that low rr tires typically are not very good for "handling" -- in other words for spirited responsive driving: many people complain about the "feel" of low rr tires, and that has little to do with inflation pressure and more to do with tire construction and tread materials.

The OP's question asked about using a different type of tire (and the the limitations of doing so) rather than the simpler question of how much air do you put in your tires. You seem to be obsessing on the inflation issue, completely missing the point of the OP's question.

Given this is an engineering forum, then supplying the hard data regarding the range of Crr figures (which are in an essentially 2:1 ratio from best to worst) then allows the original poster to say: "Yes, going to low rr tires can save far more than the cost of the tires, even if such tires carry a $200 premium per set." (etc) He can further say "Yes, given the huge differences in rr available, it would make tremendous sense for car manufacturers to equip their cars with low rr tires. But there are no free lunches, and low rr tires are typically not as sticky as high rr tires.

All this talk about inflating existing tires to the maximum load pressure even when the car is lightly loaded is not on topic, and this particular post (#15) is additionally gibberish, because, if you reread my posts, at no point do I suggest that Joe Blow needs a pyrometer. Instead, I correctly state that engineering of tires and suspension setups makes heavy use of pyrometers, it is the standard method for seeing the load distribution across the tire.

Pyrometers have nothing at all to do with environmental temperatures in the sense of your rant: In all the car manuals I have seen, there is only different pressures shown for different loads. I have NEVER EVER SEEN different tyre pressures for winter or summer, tropics or North pole........so it would appear that the GREAT majority of the people involved in car and Tyre production for road vehicles do NOT see a need for such accuracy that you seem to follow for yourself.....I wonder why??? Pyrometers are not routinely used to measure absolute temperatures, but rather differences in temperatures across the tread to infer tread load distribution. Nowhere have I suggested that I use a pyrometer routinely to measure tread temperature. Nowhere have I suggested that anyone use a pyrometer routinely to set tire pressures.

What did you misread that indicates that I think that people should carry around pyrometers? My mention of pyrometers has to do with discerning whether handling is influenced by tire pressure and whether there can be an "ideal" pressure for a tire that is something other than the pressure you seemed to be recommending (namely the pressure for a fully loaded vehicle). My point is that your recommendation is not supported by science. Real engineers using real engineering tools, come up with different pressures for different loads for very good reasons. You are welcome to re-engineer you car -- but don't expect engineers to support your contention that you should ignore the manufacturers recommendations. And don't expect engineers to accept you contention the handling is "better" with greater than the recommended pressure.

To summarize, back at post 6, I said, re the suggestion for using high pressure tires (reasonably interpreted to mean low rr tires, given the fuel consumption context):

This is a very good idea, provided you are not unhappy with the handling characteristics of the new tires.

You came back with this non sequitur:

I really have never noticed any negative handling differences with running at the highest recommended presures.....only positive ones.

This is a non sequitur, because the OP was asking about the use of new tires and suspension mods to compensate. He was not talking about the benefits of pumping a tire up to the recommended or slightly higher than recommended pressure. So in context, your remark is both potentially unsupportable and off topic. The only way you can support your contention that tires overinflated to the full load pressure when driven at light loads have no negative handling differences would be with some data. The standard method for determining when a tire is overinflated (by an engineer) is to use a pyrometer. If you are proposing that the engineers are wrong, and that you are right, and that cars should be run with the tires overinflated for the load, then the appropriate instrument for making that engineering change (Joe Blow does not re-engineer his car -- he just follows the recommendations of the manufacturer) is a pyrometer, a standard engineering tool.

Personally, I have no need for carrying around a pyrometer -- I follow the manufacturer's recommendation -- no pryometer needed -- I know they've already done the work.

Re-read your posts. Is there anything in them that answers the OP's question, Yes,I know it will cost much money,but wouldn't it be paid back after about 100000 k.m?!

It seems a reasonable answer is "Yes.... although you must weigh trade offs generally associated with low rr tires." I don't see anything in your posts that makes a stab at answering the OP's question. All you seem to be doing is criticising my response.

Sorry for the long ramble... if I had more time, I'd edit it.

I was actually relating my experiences (no recommendations for anyone else to follow!) in over 35 years of driving and owning cars.

You mentioned this in one of your posts:-

I think that is generally true, although a pyrometer might show that lower pressure is better for ultimate grip.

Who needs "Ultimate Grip" on the road, only "Boy Racers" who tear the place up.

I maintain that if a tyre is inflated within the limits as stated by the car manufacturer (the only point I ever tried to make but was seemingly ignored mostly), there is a greater difference in "grip" between different tyres of the same size and class from different manufacturers from the best to the worst…..than such an inflation procedure....

I read carefully of the ADAC Tyre tests made twice a year in the monthly magazine I receive from them!!!

I personally follow the results of these tests most carefully and take the most recent magazine with me when buying new tyres and have done for many years…..

I select a tyre that is probably one of the top 3 best in its class, looking also for good roadholding particularly in the wet, wear and noise characteristics.

Sometimes the "best" tyre for me is also not the most expensive of all, which is a nice return if possible, but price is never an initial deciding factor, only when there is a choice of 2 or more that are basically the same performance otherwise!!

Let me categorically state, that when using the maximum recommended tyre pressure from the manufacturer of the car in question (which is an across the board value for any make of tyre of that size that can be legally put on that car!!):-

I HAVE NEVER HAD MIDDLE OF THE PROFILE WEAR NOR HAVE THE TYRES WORN OUT IN ANY WAY EARLIER THAN EXPECTED, NOR WAS THE HADLING AFFECTED IN A NEGATIVE WAY..

Often I have achieved mileages that are double or even triple those of my colleagues driving identical cars (when I drove company cars!)… I do feel that my senses of the cars handling are reasonably good as I would notice some differences in handling between 16 " Winter types and 17" Summer tyres, but none of my colleagues could!!!!

I feel we should agree to disagree on this matter, each to his own.....

Bravo!

I've begun using new model tires because of the reports of dealers selling ancient tires for new, even though I know the difference.

With high profile tires, you get better handling with higher pressure. The side wall is stiffer to allow higher cornering speed. Learn that in autocross.

If anyone gonna try this, make sure you fill the tire up when its hot. Say after 30 min of driving. You don't want to gain a few psi after tire get hot and it get pass max limit.

There is no need to pump up when hot PROVIDED you only use the highest recommended tyre pressure from the car handbook. Its a "cold" pressure that takes into account any possible extra pressure due to tyre "warm up".

"Tyre warm" up is by the way, MUCH less when running a higher pressure as the tyres do not "work" as hard as when a lower pressure is used.....which is part of the reason that you get a much higher petrol AND tyre mileage!!

Many people NEVER understand that ONLY under inflated tyres explode, not over inflated ones!! At least not when over inflated to the maximum allowed by car handbook.

Under inflated tyres over heat, start to melt and then explode!!!

Perfectly correct, but very few others would appear either to know or understand!!!

I have helped at several accidents where tyres have overheated and exploded and also managed to stop several drivers just BEFORE it happened, over many years!!!

I gave you a GA as well.....

Hello Bwire:

I was wondering if you run these 110 psi tires close to that 110 psi rating and how do they work for ride and MPG? Are these on a truck, SUV or car?

Thank you for any advice.

Hello Senatorferrell,

They are on a class "8" vehicle on the steer tire position @ 110 psi with 105 psi on all other wheel positions year round with best result of mpg, ride, performance characteristics and wear in CONUS.

As Andy has related vehicle manufacturers recomend specific type tires for their products and tire manufacturers give the suggested inflation pressure. These inflation guides are exactly that, a guide as wheel position and or vehicle weight may determine the correct inflation more accurately.

Ubetcha!