Running with over inflated tires to get better MPG...will I ruin my tires ??

Hello guys
I read in the sticky that running your tires to90% of their maximum tire pressure written on them will help you get better mpg... i understand the point but will that ruin my tire thread in the center of them? Thats what I always learnt about over inflating tires...

Thanks
G.b.

I have never noticed tread wear issues on my vehicles, and I have been running ours at 40+ PSI for years now. Will be interested to hear the other responses.

guillaumeber said:

Hello guys
I read in the sticky that running your tires to90% of their maximum tire pressure written on them will help you get better mpg... i understand the point but will that ruin my tire thread in the center of them? Thats what I always learnt about over inflating tires...

Thanks
G.b.

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You will see more wear in the center if you max out the sidewall pressure. You will also notice a weight load with that maximum sidewall pressure. How much weight, people/stuff do you normally carry ? The more weight the higher tire pressure you should run them at. Your tire pressure is on the drivers door jam. But that is the pressure with the original tires. Higher pressure in most tires means a harsher ride. Experiment with the pressure to give the best ride and mpg or lt/100km. Also remember if you run with just air as opposed to nitrogen that air will heat up. Increase in temperature will increase the air pressure inside the tire. On a long trip with hot ambient you can see as much as a 4 psi rise above the cold tire pressure.

The simple answer to your question is that it depends on how over inflated the tires are. Recommended tire pressures are usually a trade-off between safety, tire wear, and ride comfort. The actual "perfect" pressure will depend on the tires, ambient temps, load, how you are driving, and probably other factors.

The point is: a little higher than the recommended pressure will make little or no difference in tire wear. Too high pressure will cause the center of the tire to wear faster than the edges (too low pressure can do the opposite). An additional 5 psi will probably do no harm. Never exceed about 80% of the maximum pressure rating on the tire. Tire pressures are always measured with the tire cold.

Have Fun!

Don

It also depends on the tyre design. I bought a set of second-hand tyres in a different size for the car, there was a mix of tyre models ... one of them was a brand-new but cheap budget tyre, and the rest were michelin energy. The budget tyre bulged out at 45psi, whereas the michelins were ruler-flat. Needless to say, I replaced the budget tyre before they went onto the car.

guillaumeber said:

Hello guys
I read in the sticky that running your tires to90% of their maximum tire pressure written on them will help you get better mpg... i understand the point but will that ruin my tire thread in the center of them?

Click to expand...

Nope. The bulging tread problem was for bias ply tires which are now long gone from the market. Radials do not bulge in the center of the tread with increased inflation pressure.

Cogen Man said:

You will see more wear in the center if you max out the sidewall pressure. You will also notice a weight load with that maximum sidewall pressure. How much weight, people/stuff do you normally carry ? The more weight the higher tire pressure you should run them at. Your tire pressure is on the drivers door jam. But that is the pressure with the original tires. Higher pressure in most tires means a harsher ride. Experiment with the pressure to give the best ride and mpg or lt/100km. Also remember if you run with just air as opposed to nitrogen that air will heat up. Increase in temperature will increase the air pressure inside the tire. On a long trip with hot ambient you can see as much as a 4 psi rise above the cold tire pressure.

Click to expand...

Boyles law applies to any gas.. As the tire heats up, that heat is transferred to the gas filling the tire. Air or nitrogen it does not matter. Pressure goes up with increased temperature. That's why you check the pressure on cold tires.

migbro said:

Nope. The bulging tread problem was for bias ply tires which are now long gone from the market. Radials do not bulge in the center of the tread with increased inflation pressure.

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Correct. Especially with steel/amarid/etc. belted radials.
I don't run over 40 psi in my TDIs because the road conditions here make for rough/harsh ride, especially in colder temps. Mileage certainly is better with higher than the oem recommended psi.
Run my Suburban tires inflated to close to max sidewall psi. Never had any center wear issues, in fact wear has been very good considering its use. Ride quality isn't much of an issue with that bus.

I talked to some guys from Michelin last year, and they weren't very happy with my question 'is it OK to run my tyres at 45psi instead of the recommended 30psi' . Their main concern was that grip would drop, they didn't mention centre wear.

Paint a white line across the tread and see if the center of the painted line wears away quickly.

I ran mine at 44psi (max recommended pressure on side of tire) for an 800 mile road trip and saw very noticeable wear on the center and inside of my front tires. Alignment is fine I get it aligned very frequently because I have lifetime alignment. It doesn't do this if i run 32psi like normal. Next road trip I'm probably going to air them to 38 or so.

So yes, it is my experience that running abnormally high pressures in tires will increase tread wear. I did get 47MPG on that 75+ mph highway trip though. Not bad.

turboboost1 said:

Boyles law applies to any gas.. As the tire heats up, that heat is transferred to the gas filling the tire. Air or nitrogen it does not matter. Pressure goes up with increased temperature. That's why you check the pressure on cold tires.

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Boyles law will apply, but not to a noticeable extent. Nitrogen will not increase in pressure anywhere near as much as regular air would. Where as a gas like CO2 would increase and decrease in pressure way more for a given set of temperatures.
I dont run nitrogen because I feel it is a cash grab for the shops. but it is a good product for those that are too lazy to check tire pressures at regular intervals.

SkyRyder55 said:

... Nitrogen will not increase in pressure anywhere near as much as regular air would. ...

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Why do you say that? My understanding is that it would behave in exactly the same way as normal air (after all, normal air is 80% nitrogen anyway).

MikeMars said:

Why do you say that? My understanding is that it would behave in exactly the same way as normal air (after all, normal air is 80% nitrogen anyway).

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Nitrogen is dry. No moisture.

co2 is a dry gas and nitrogen is also a liquid under the right temperature and pressure

air vs. nitrogen pressure change differences are so minimal that a driver will not be able to detect them

different gasses behave in different ways as far as expansion at given temperatures and pressures. Refrigerants are the same thing. And it is the basis of refrigeration. but that is a whole different topic.
Needless to say, nitrogen is a very stable gas as far as volumetric expansion due to heat.

Cogen Man said:

Nitrogen is dry. No moisture.

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Neither would normal air, if you ran it through a dehumidifer or whatever.

SkyRyder55 said:

different gasses behave in different ways as far as expansion at given temperatures and pressures. Refrigerants are the same thing. And it is the basis of refrigeration. but that is a whole different topic.
Needless to say, nitrogen is a very stable gas as far as volumetric expansion due to heat.

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all of this is true in a laboratory but imperceptible differences under road conditions. that's what independent labs testing nitrogen vs. air find.

people are making way too much of this "nitrogen is dry" claim because CO2 is *also* a dry vapor (even without having to run it through a dehumidifier). Refrigerants are not comparable to tire pressure...that much should be obvious given that they're held under hundreds of pounds of pressure per square inch.

no but refrigerants are a comparison based on how they expand and how much different refrigerants expand based on temperatures and pressures.
CO2 when compressed is a liquid.
The other advantage of Nitrogen in tires is that it is less prone to leak out of the tire over time due to the larger molecule size. Yes air is mostly nitrogen, but you will have less leakage with pure nitrogen in a tire.
Im not in favor of Nitrogen in tires. so dont think im trying to promote it. The advanteges gained by it are minimal at best.

as I wrote earlier, nitrogen is a liquid when it's compressed, as well

under normal operating temperatures and pressures the composition of gas in a road tire will not make it expand at noticeably different rates from any other gas

bizzle said:

under normal operating temperatures and pressures the composition of gas in a road tire will not make it expand at noticeably different rates from any other gas

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If thermodynamics and applied thermodynamics taught me anything, then this is a true statement. I just did some math, and any gas undergoing a 15C (60F) change inside a car tire will change the tires pressure by about 2psi assuming a tire volume of about 10L.

I have always been under the impression that people use nitrogen because it has a physically larger molecule that wont slowly leak out on a microscopic level over the weeks/months/years. I dont know if there is any truth to that, but hopefully you check your tire pressure more often than nitrogen would even make a difference to.

The atomosphere is 78% nitrogen anyways, so your paying extra for the other 22%.

I must add that most of the shop I saw didn't really vacuum the air that was already inside the tire before inflating it with nitrogen... so there is a large quantity of air already inside... the nitrogen injected is only a part of the total content inside the tire...

to the thread's question:

I over-inflated my wife's metro tires and it did increase her mpg but also wore the center track so badly that it was completely gone while the outer tracks only looked halfway worn. I attributed that significant difference to the light weight of the metro. I'm not going to do that as much with the new tires she has on there.

I wouldn't do it on any car I planned on doing any spirited driving in.

The best article that I ever read on this subject was written by a State Trooper that taught high speed driving to other troopers. He said that would always start by having the troopers drive the course with the tires set at the recommended car manufacturer rating. Then he would have them get the maximum pressure rating for the tire & increase it to just below that. He said they always found a significant increase in handling plus you get improved MPG. I have only used Michelin tires for quite some time and run them at about 90% of max & have never noticed any wear issues.

Have any drivers with nitrogen filled tyres measured their tyre pressures before and after a long run to see what the pressure difference is? I'd be astonished if it wasn't virtually identical to that of air filled tyres.

couple observations: first, refrigerant gasses/fluids make great use of the heat of evaporation, which involves phase change between gas and liquid.

and the ideal gas law works pretty well on all gases, including water vapor.

PV=MRT

the pressure is equal to the sum of all partial pressures from components.

MR is a constant for the specific number and type of molecules.

leaving PV directly proportional to T (with T expressed from absolute Zero)

so for a given volume, (like the inside of a tire) P is directly proportional to T.

if you have 25 PSI at 250 degrees K (-10 f)
it will be 32 PSI at 320k (+116 f)

if you had liquid water inside the tire, it would be a bit different, But I doubt this is an issue for most of us. and liquid nitrogen or oxygen is out of the question.

the Nitrogen idea does let you be a bit less attentive on checking pressure, but you still have to keep an eye on the pressure as temperatures change.

and I prefer the recommended pressure. higher pressures give me a ride quality a bit too harsh. gee, why do you think they are recommended?

meerschm said:

the Nitrogen idea does let you be a bit less attentive on checking pressure, but you still have to keep an eye on the pressure as temperatures change.

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Good point.

The question was:
Running with over inflated tires to get better MPG...will I ruin my tires ??

No.
Unless, perhaps you "overinflate" over the sidewall max psi, although I think the harsh ride would irritate you enough that wouldn't come into play long enough to "ruin" the tires.

lets see...Between my previous car and this one, over the course of about 100k of running 40+psi in the tires the center sections have not worn out significantly more than outside.

The previous cars tires were so nice after 30K on them that i took them off the Maxima and had the installed on my moms Volvo as summer tires.