Those calculators are good for an approximation, but each brand (or model)
will have a unique specification.  You should be able to find the actual
specification if your tire is still in production.  Tire Rack (tirerack.com)
is really good at providing this type of information.

Cheers,

Jeff

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Alistair Bell
Sent: Friday, October 14, 2011 7:55 AM
To: vanagon@GERRY.VANAGON.COM
Subject: tire size calculator Re: tire circumference

bookmark it Dave :)

http://www.miata.net/garage/tirecalc.html

alistair

On 2011-10-14, at 7:16 AM, Dave Mcneely wrote:

> I once knew a web site where one could enter a stock tire size and a
replacement size, and get an odometer and a speedometer conversion factor.
BTW, the difference is so slight for 185R14 vs 195R14 as to not be of
practical significance.  But when folks go to the larger wheels and tires,
it really matters.  mcneely
>
> ---- Robert Mac Dowell <yakandhike@COMCAST.NET> wrote:
>> Let me rephrase that. How many RPM'S should it be for the speedo to be
right
>
> --
> David McNeely