Guy,
You're correct, of course, but I think it's difficult to come up
with a reliable allowance for that "flat bit at the
bottom". These factors could include the pressure the tyre is inflated
with, the load in, (and of), the vehicle
itself, and the variable of how much stiffness the maker builds into the
tyre walls.
If there is a formula to take account of the above, (and possibly
other factors like height above sea level)),
I'd be delighted to hear of it.
It strikes me that having arrived at the unloaded diameters, one
would have to take actual measurements
when the wheels is on the car, (from the hub centre down to the ground) in
order to make a comparison. However,
at that point, you would, most likely, have already bought the new tyres!
My calculations, at least, allows one to make an informed decision
on paper, before purchase.
Best regards,
Ron.
===>
At 08:49 15/12/2003, Guy Weller wrote:
>Ron,
>you haven't factored in an allowance for the flat bit at the bottom of the
>tyre. It reduces the radius.
>Guy
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