How much of an increase in mpg can I expect with overinflated tires?

[Ernie Rogers]

Originally Posted by theclencher

patch size is largely a function of weight on tire over tire psi

Hmmm, that's right--- the load on the tire is equal to the force at the pavement, which is pressure times area: F = P A

wider tire, all else equal, will have same size patch area BUT different shape- wider and narrower front-to-back.

Yes, the area will always be the same. The question is, how does the flexing of the rubber compare? The strain in the rubber is generally proportional to the energy loss. [Energy loss = (1-k)(strain energy) where k is the coefficient of restitution.]

ernie: skeptical about dbl psi/half rr claim. also don't agree with not exceeding max sidewall listed psi

Think it through and you will conclude that the amount of strain is equal to the patch area, which is inversly proportional to the tire pressure.

Okay, we can disagree on exceeding side wall "max pressure." I prefer to believe that the engineers that set "max pressure" really meant it.

on point 2 ya really hafta get nuts on oversizing tires before it throws the speedo off by more than a few mph

I want to know who told you I was crazy-- but it is about getting good mileage, not tire size. :-)

on pt 3 i posed this question some time ago and the answer was lo pro tires roll EASIER.

The question again is which tire has less total strain in the rubber. A tall sidewall accomplishes the needed deflection (to make the flat patch) with much less distortion needed. I will grant that the low sidewall can be made thinner, which helps in the other direction. But, most people have reported lower fuel economy with low profile (= low aspect ratio) tires.

on pt 4 if you return new tires cuz fe goes down you may never end up with new tires!!! cuz worn tires have lower rr. it's tough for new ones to beat that

Aahahaha, that's correct. You will have to use some judgement here.

Ernie Rogers

[omgwtfbyobbq]

Originally Posted by Ernie Rogers

Okay, we can disagree on exceeding side wall "max pressure." I prefer to believe that the engineers that set "max pressure" really meant it.

I think it's safe to say that the max pressure also corresponds to the max load, at the max speed, on a pot-hole ridden road, during a Death Valley summer day, plus some safety margin. By figuring out what the pressure is during those conditions, and comparing it to the conditions we tend to ride in, such as moderate weather, a max speed of ~65-70mph, less than max load, I think we can take a decent stab at how much cold overinflation is still safe for ourselves.