The Miata.net tool directly calculates revs per mile but does it
inaccurately. Other tools do it and get results that match the real
world. Why the tool always gives bad data matters little. There are much
better tools that cost the same.

Mark

Mike S wrote:

>
> It is simply being misused. The Miata site calculator is intended to
> compare different tire sizes, not give correct absolute results, and is
> pretty accurate for that.
>
> Tire size can't be used to directly calculate revs per mile - as soon
> as you put a load on a tire, it flattens on the bottom. That reduces
> the rolling radius, and it will do more revs per mile. That's why the
> calculation underestimates.
>