Hi to all,
Just wanted to follow up and pass on my own personal info on my selection of speedo gearing.
OK - My '73 Mustang 302W vert runs a factory C4 trans with an 8 tooth drive gear. (verified)
My rear tires are 295/50 on a 15 inch rim. That gives 26.6 inch diameter of infated tire under no weight load.
My diff has just been upgraded to Tru Trac Posi with a 3.25 ratio. (the old factory ratio was a 2.75 i believe)
That new combo has thrown my mph speedo reading out close to 6mph too fast. The original factory driven gear was an 18 tooth.
Based on the Internet speedo gearing calculators, they told me a 20 tooth driven gear would be just right to bring my speedo
back to an accurate reading. I bought a 20 tooth driven gear, installed it, and it has proved to be giving me now an accurate reading again
based on many Sat Nav tests conducted by myself.Very happy with my results.This setup has worked for me.
So for all you guys with a similar setup to mine specs wise, this will work for you also.
Many thanks,
Greg.