underinflating for increased performance

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I'm more concerned with braking and handling performance than with fuel economy. To me, a car that performs better is safer.

To that end, would it be a good idea to underflate the tires during the dry months? (to increase the contact patch size). If so by how much?

The car is street-driven and not driven hard.
 
Underinflated tires run hotter than properly inflated ones, developing excessive heat that leads to tire failure. An underinflated tire also wears abnormally, with the tread on the outside edges of the tire wearing faster than the tread in the center of the tire. Driving on underinflated tires can cost you up to a mile a gallon in fuel economy because it takes more fuel to overcome the rolling resistance of a partially inflated tire. It is also dangerous. Driving on underinflated tires adversely affects handling and the tire can overheat and blowout.
 
Underinflated tires will perform worse in wear, mileage and handling. The only thing that may improve is ride. A tire's dynamics are worsened with underinflation mostly because of stability in the sidewall. In turns, the tire can/will/has a tendency to deform and begin to roll onto its sidewall if underinflated.

While you should not/never inflate a tire to its maximum rating, inflating them over the mfgs specs can improve handling. This can however increase wear as the center will wear out faster.
 
Originally Posted By: digitalSniperX1


While you should not/never inflate a tire to its maximum rating, inflating them over the mfgs specs can improve handling. This can however increase wear as the center will wear out faster.


Agreed. Using common sense, inflating tires over the door sticker PSI recommendation (and at/below maximum sidewall pressure) does result in sharper handling. When doing so, do pay attention to how the tire is wearing.

The only reason to under-inflate tires is in very deep snow to float more, or when rock-crawling to grip the rocks better.
 
Many performance cars recommend higher pressure if driving above 100 MPH. My E430 recommends 32F/33R for normal driving and 36F/42R for speed above 100 MPH. When I go to Vegas I usually have 42F/44R because whenever I had a chance I would go above 100 MPH and the car was very stable. For normal driving on local highways I have 38F/36R, the car performs much better than 32F/33R.
 
Similarly, my Audi has an actual recommended inflation number if the car is loaded with people/things.
 
Originally Posted By: dparm
Similarly, my Audi has an actual recommended inflation number if the car is loaded with people/things.


Yup, same thing with my BMW.
 
Is there any scenario where 'slight' under-inflation* would provide a temporary 'advantage', in any scenario/circumstance?

*Definition of under-inflation: Lower than recommended PSI for front/rear according to the owner's manual.
 
Originally Posted By: ltslimjim
Is there any scenario where 'slight' under-inflation* would provide a temporary 'advantage', in any scenario/circumstance?

I've seen people do it on trucks to improve traction in snow or sand. This assumes driving at relatively low speeds so that the tires don't overheat.
 
Originally Posted By: ltslimjim
Is there any scenario where 'slight' under-inflation* would provide a temporary 'advantage', in any scenario/circumstance?

*Definition of under-inflation: Lower than recommended PSI for front/rear according to the owner's manual.

Severe off-road application. Think "Rubicon".
 
When I was racing, there were times I would slightly underinflate my tires, knowing the pressure would come up with temp. I did not use tire warmers. I ran the cold pressures that Michelin recommended for race conditions, which was lower than the vehicle mfg recommendation. In this particular case 29 rear and 31 front.

On my current street tires (Cont Extreme DW), running low or even correct pressure I experience too much understeer which in my case can be minimized by bumping the front up to about 36 psi. It seems the sidewalls are just too soft.
 
Tony,

I am hoping you got the message that using pressures under the vehicle tire placard is the wrong direction for performance. I am also hoping that it is obvious that there is a point where there is too much pressure.
 
Umpteen jillion taxicabs ran underinflated tires to get a false higher mileage reading on the odometer.
At slow speeds and no strain, it's OK, I guess.

But I would always go for standard or a little over in my cars.
Better handling and braking, for sure. And almost always better wear.
 
Originally Posted By: mechtech2
Umpteen jillion taxicabs ran underinflated tires to get a false higher mileage reading on the odometer.
At slow speeds and no strain, it's OK, I guess.


If I did that on the cabs, my dad would have paddled my behind to the point I still couldn't sit down. He mandated daily pressure checks.

Taxis, properly maintained, are a nice way to see how long a decent set of tires can last when properly rotated and inflated. My dad was not big into underinflation or overinflation. Both can create weird wear patterns, and my dad always hated the harder ride of overinflation.

I still hear guys say, "But the sidewall says 50 psi!" Sheesh.
 
Originally Posted By: tonycarguy
I'm more concerned with braking and handling performance than with fuel economy. To me, a car that performs better is safer.

To that end, would it be a good idea to underflate the tires during the dry months? (to increase the contact patch size). If so by how much?

The car is street-driven and not driven hard.


The problem is with street-driven you can not heat the tyres enough to gain the pressure for tyre operating optimally. You only can do that on the circuit, but this will definitely impact on the life of the tyre too.
However, if you drive quite aggressive for street driving, you still can try 1-2 psi lower than placard, and check the hot tyre pressure.

Here below is the Michelin article that can help you:
http://www.tirerack.com/tires/tiretech/general/Michelin_Care_and_Feeding.pdf
 
Originally Posted By: ltslimjim
Is there any scenario where 'slight' under-inflation* would provide a temporary 'advantage', in any scenario/circumstance?

*Definition of under-inflation: Lower than recommended PSI for front/rear according to the owner's manual.



People who drag race their cars pure stock, with stock, or (REAL) street tires will lower the rear pressures below the placard rec., and increase their fronts to the sidewall max, or more (given a RWD car in order to get rear grip, and decrease front rolling resistance).
Of course, this is only for the 1/4 mile, and is only being done for a quarter mile of straight line driving at a time.
wink.gif
 
Originally Posted By: tonycarguy
I'm more concerned with braking and handling performance than with fuel economy. To me, a car that performs better is safer.

To that end, would it be a good idea to underflate the tires during the dry months? (to increase the contact patch size). If so by how much?


The size of the contact patch is only one variable.

As you reduce the inflation the tire can't maintain its shape and the sidewalls increase their flexing. That causes heat and reduces tread life, reduces fuel economy, increases the slip angle of the tires causing a loss of steering precision and cornering stability.

Going the other way, overinflating a tire makes the sidewalls stiff and unyielding and reduces the contact patch. They can be damaged more easily when hitting potholes or debris in the road and the vehicle rides harsher. However, up to a point you’ll see an improvement in steering response and cornering stability.

If you want better braking and handling, going higher rather than lower is the correct approach.

Effects of Underinflation on Contact Patch
 
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