Quote:
Originally Posted by gpsman1
The tire pressure in your tires DOES NOT change the distance (perimeter) around the tire!!!!
The perimeter of the tire is 2000mm. Flat = 2000mm. 45psi = 2000mm.
Only the shape changes with pressure changes.
The more air pressure you have, the closer to a circle with 2000mm circumference you have. Less air = a longer flat spot on the bottom.
No matter what pressure you have, the distance around the tire, and your MPG or odometer is NOT affected.
( As the tire tread wears off, your tires will get slightly smaller. )
-John
P.S. It may help to visualize your tire like a tank's tread. No matter how many rollers the tank has, or the shape of the tank, the tank tread length never changes to make one revolution. The distance traveled for your tire tread to make one revolution NEVER changes.
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That does make the presumption that the tread on a tire cannot stretch... which, now after I've thought about it, is likely true since all tires are steel belted these days. I doubt the steel belt would have much give in it at all.
Lacking the steel belt the rubber could stretch SOME.... but probably not much since the tread rubber is pretty thick. Bike tires for example definitely have different circumferences depending on inflation pressure, which is why you have to adjust the speedometers for distance if they use a magnet to count tire revolutions (it says that in the manual I have for mine). But of course Bike tires aren't steel belted and are a heck of a lot thinner.
I hadn't thought of the steel belt when I posted and was thinking of that bike speedometer at the time.