On Nov 17, 2008, at 7:48 PM, Benn wrote:
Awright, my 2 cents:
If your tire were a 1-mil-thick balloon, then the approach strictly
using
tire pressure might be appropriate. But tires aren't balloons--e.g.
"run
flat" tires can have zero pressure and still have close to the
original tire
patch. Obviously stiffer (and/or shorter) sidewalls are required for
run-flats (I don't think they make any 70-series run-flats), so the
sidewall
stiffness has a LOT to do with it. And said sidewall stiffness will
therefore influence the contact patch....I'd be v. surprised if you
found a
tire that had anything approaching a linear relationship between
pressure
and contact area, unless you're looking at a v. small range.
Benn
opinion worth what you paid for it, and two cents ain't much
Okay, Benn-- you got me there. I have been ignoring the amount of
load that is supported by the sidewalls. I had assumed it was
negligible (and, for that matter, I thought run-flat tires have a
solid filling rather than using just the strength inherent in the
sidewall construction to support the load.
And yes, I admit that the 1-mil balloon is close to an ideal tire for
the sake of this discussion. But -- compared to a fullly-inflated
tire -- how much load will an empty tire support? Is it enough to be
a real factor in this? If the tire can support 1,000 pounds at proper
inflation and 50 pounds when at atmospheric (hey, just a wild-a**
number thrown in for the sake of the discussion) -- you're talking a
five percent error in the contct patch/tire pressure equation.
Significant -- but not all that much in the grand scheme of things.
Jon Wennerberg
Tall guy with moustache
and a pair of 2 Club hats
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