Thanks to all for the replies.  

It's less to do with the wheel size and more to do with the TPM of the speedo head. Obviously both are involved in the calculation, but the TPM has most input  

The Guessworks calculator is based on theoretical rolling radii, not empirical ones. It's not 100% accurate, but at 95% or better it'll do. 

I've never had to fit a 5-tooth gear as they are generally for Metros. 

That calculator on Guess Works is excellent. I used it on my car and the speedo is exact. The other discussion on the 5 speed transmission made me wonder what you do with that last speed. I can do 80mph in 3rd and still be below 6000 rpm.

Jerry

This is what I ordered from John for both the ten inch cars:

you ordered a 7/16 combination, in January 2010... fortunately I do keep records.. lol

For the 3.1FD on the 1408tpm speedo ( I assume early mini cooper on 10" wheels ) yes, the 7/16 combination is correct.... 

Terry

Most of the time, we tend to install what we have and see how it reads, then see which way to correct it.   If you think about it, very few 10" wheeled cars had the option for 3.1 gears, so most speedos wouldn't be right anyway!  Tiny wheels went away in 1984 when making Minis stop became a priority!  That was mostly before the push to drop RPMs with taller gears.  I think I installed a six tooth pinion in my car, but ended up running 3.76 gears and 13" wheels.  My MK1 S shows 110 MPH at about at about 4000RPM (actual speed probably 60-65!).... probably impossible even for my hot rod 1380!!  That would be 200MPH at about 7500.... not gonna happen!

The other problem is availability, or rather lack there of!  When I built the engines here, I had bins of spindles and little pinions. Then suddenly all the cores I got had them removed!  Now rare as hen's teeth and priced as such!  If your speed reads too fast, just changing the spindle to a 5 tooth should get you close!

Don't you need the TPM of the speedo first?

Terry

I think you need a 5 tooth drive pinion and one of the 'beige' colored plastic gears... can't remember how many teeth...

Agreed.

//www.guess-works.com/

 

I believe guessworks was the website that had the information you need.

Does anyone know which speedometer worm drive/pinion combination would work for 3.1 final drive on 10 " wheels?