"Jeff Wisnia" wrote in message
...
| Now Carl, that explanation is what I had trouble with in the first place.
|
| Imagine if you would that the tire had side to side notches on the tread
| like an inside out timing belt and the pavement had mating pitch grooves
| on it. (Sort of like the ones which make a warning sound if you start to
| wander off the side of the road?)
|
| That would create a "rack and pinion" configuration.
|
| Would you still say that the number of revolutions per mile that tire
| makes would vary with the air pressure in it, or as you put it "the
| effective radius".
|
| That's where my skepticism to the "Car Talk" answer stemmed from. I
| don't doubt that second order effects come into play to make the
| rotations per unit distance increase somewhat with lower tire pressure,
| but I'm willing to bet that the effect is nowhere near as large as being
| fully inversely proportional to the rolling radius, at least not until
| the tire jumps right off the rim.
|
| Jeff

Believe me, I have a bit of trouble getting it, even visualizing it, but
there's really no other way to see it. The difference in rotational speed
has to be taken up in the wrinkling in the tread and all the sidewall
flexing, which is why a low tire is a very bad thing, since all that action
creates a lot of heat.