Quote:
Originally Posted by crystalworks
While I agree that I'd personally prefer finding a solution other than lowering tire inflation, I always thought contact patch got bigger, not smaller with under inflation. As Andrew's math illustrates. Though sidewall might roll slightly more in HARD cornering I don't think 29psi is going to cause any major problems. I prefer getting max mpg so run slightly over inflated.
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Generally, contact patch gets larger as inflation increases. But there is a point of diminishing returns. The converse is true that under inflation typically reduces the contact patch. Usually, within reason, the risks associated with over inflation are less so seeking better mileage by adding a few pounds of air can help MPG and is reasonable. I've tried some over inflation for long trips to see if I can increase mileage. Increases were not significant in my case.
In this case we are discussing contact patch in an emergency situation of braking or cornering. When turning the tires rollover to some extent. The more abrupt the turning the greater the load increase so in an emergency situation of cornering the contact patch reduces accordingly. If under inflated the contact patch will move toward the loaded side of the tire reducing the load on the unloaded side and the contact patch. The construction of the tires vary, so how much inflation it takes to reduce or increase contact patch also varies as does the point the tire breaks loose and how much it reduces stopping distance. Depending on the amount of under or over inflation determines whether adhesion is lost in an emergency situation or just regular driving.
The effectiveness of a given tire is subject to several other important variables. When discussing inflation it is important to differentiate between cold tire inflation and the normal operating temperature. Under inflation generates more heat so the change from cold tire to normal temp is greater. Outside temp is also a factor in how much the inflation changes. Most tire manufactures list 35 pounds as maximum inflation and they warn about the risk of under inflation right on the tire. Generally, too much under inflation is more than 10% of the max or 3.5 pounds.
Comparisons here should be apples to apples. As an example comparing what works for an E46, a 6 to an 8 cylinder X5, or one with sport suspension and one without don't necessarily apply. There is no one size fits all. It should be an apples to apples comparisons.
All I'm saying is there are tradeoffs, including safety, that should be carefully considered when making a decision to be outside of the manufacturers stated inflation parameters.