Yes, we have been over all this before. That simple arithmetic gives one
value while the real world tires are something else. That program gives
rev/mile results way different than every tire company specification I
have checked.

Some other programs manage to give results that much more closely mirror
what the tire companies test results say. I would use one of those other
programs if data accuracy is important to you.

This 1010Tires program gave good numbers for all the sizes of interest
to me. By good numbers I mean numbers that fall within the range of
specs given by various tire companies for their tires of a given size.

http://www.1010tires.com/tiresizecalculator.asp

Mark

Alistair Bell wrote:
> funny, when i do it long hand I get 786 (for 80 profile). I must be making the same mistake as the miata calculator is doing.
>
>
> let me work it out here:
>
> 185 mm = 7.283"
>
> 80% of that = 5.826"
>
> add that twice to the rim diameter of 14" = 25.652" (overall tire diameter)
>
> circumference is diameter X pi = 80.588"
>
> inches in a mile = 63,360
>
> 63360/80.588 = 786.22
>
> alistair
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