one question I have had for a while is why do vanagon speedometers have a range of revs/mile numbers on them? I have 2 old ones in my parts bins (mph), one has 820 and one has 805.

And of course, syncros are different. MY '86 with a purely kph speedo, has 1000 on it. I guess I should look for go kart tires :)

alistair

On 2011-10-15, at 7:29 AM, mark drillock wrote:

> 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.
>>