I have a 68 RS convert. It has been garaged for about 10 years. I just put it in the shop for some major restoration. I was searching sites recently and i saw a great table that listed the conversion callibration tables for tire size, rear end gears, etc. to properly callibrate the speedometer. I cannot find it now. If someone remembers this site, i would appreciate the link. Thanks. Richs68.

I've used the table for an idea of where to start, but I've always (approx 10 cars) had to change the speedo cable gear from what the formula calls for,..there's too many variables,..for instance, tire heigth,..is it calculated the same from manufactuerer to manaufacturer? Is it calculated fully aired up and under a load? If there is a standard, it doesn't seem to work in the formula.

We have speed monitors that show your mph here in Austin,..and if my speedo is 'under-reporting' I need fewer teeth on the gear. If it reads higher than actual, I need a gear with more teeth.

Hope this helps.

http://www.novaresource.org/speedo.htm
http://www.miata.net/garage/tirecalc.html