Quote:
Originally Posted by Sugarphreak
When it comes right down to it there is really no other way to explain why you get better MPG using higher pressures other than you are reducing surface area. Using that logic, if you reduce the surface area the points of contact will have more weight on them and will wear faster.
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This is exactly why I'm not interested in theory. I spent lots of time learning theory in physics and engineering classes, then found out what from theory actually made it into the real world. Get me some real data.
Here's more theory blah blah you haven't accommodated in your calcs - an additional reason for lower rolling resistance is less bending in the edge of the tire surface as it enters and releases from the road. Also, lower cross section means more force per area which will increase friction so in one respect, cross section could be a zero sum game (decrease in surface area is offset by increase in friction per area). In yet another, one could surmise the resistance comes from compression of the tire surface as the rubber moves through the contact patch, much like compressing and releasing a damped spring. In this case it's not the patch that matters, it's the amount of compression along the direction of travel times the width of the tire that would indicate the amount of force required to keep the tires moving (this would close to but not identical to your patch calc). My guess is the damped spring effect is likely the greatest but not sole reason for rolling resistance.
I agree the tire will only wear where it makes contact with the road (duh!) but is wear linearly proportional to force? Unless you're a tire scientist and have worked with both tests and an understanding of the materials, any commentary is all speculation. There's lots of other speculation about how much a steel belt would deflect in the middle and whether or not that effect would increase or decrease the overall useful life of the tire.
GET ME DATA!!! The hypermilers claim no decrease in useful life of the tire through overinflation, there's data that counters several forums worth of speculation, if it's true. The racers note an increase in wear in the center of tires used for racing but we don't know if this is exacerbated by race conditions or actually resulted in a decrease in useful life of the tire. If the center of the tire wears faster but I get the same amount of total miles out of the tire then I'll take the better mpg with a worn center tread.
Another factor is the newness of the tire. I've noted new tires have lower rolling resistance than old tires. Is this because of a manufacturer coating, the rubber compound being new, or the upper portion of the tread being a different forumla than rubber in the lower parts of the tread, or something else?