Re: Tire Diameter

[n9ads@domain.elided (Howard R Pletcher)]

On Mon, 01 Dec 97 17:07:22 PST8 jmbrodsky@domain.elided writes:
>        I'm not entirely sure where the number 2.5% came from in 
>     whoever's post it was.  I'm pretty sure that tire manufacturers 
>     adhere to a standard so that when the tire is loaded to it's 
>      rating   (usually like 1150-1700 lbs for an LT tire) it won't be
more than 
>     XX% of it's intended unloaded specified psi diameter.   The side of

>     the tire has a weight rating and a psi rating cold.  This has an 
>     included safety factor to allow for Brake/Road friction heating, 
>     ambient heating, atmospheric pressure, load changes, etc.   I was 
>     rather surprised to hear the 2.5% actually,  I think the number is 
>     closer to 10% reduced at load.  ie.  31" tire shrinks 3.1" loaded.
>     
>        Anyone else have ideas?  I suppose if we all called our favorite

>     tire stores we could compile quite a list of lies, only to weed 
>     thru and find the truth!
>     
>
The 10%/3.1" compression sounds reasonable-----
until you go out and measure your 31" tire.    It looks like the typical
tire would have 8" of tire height, 15" of rim, and another 8" of tire to
get a total diameter of 31".  If it compresses 3.1", that's actually a
38% compression of the tire section between the rim and the ground. 
Maybe at 5 psi you'll get that much.   The 2.5% overall results in a
.775" compression which I think is probably typical although I'll agree
with Joel that it doesn't sound like much..