Speedo TPM
Turbo Mini Forums

Hi hope you can help.....

I am trying to calculate the correct worm and pinion ratio needed for my set up. I have tryed Guess-works but it dosen't have my speedo TPM listed and cant get the minifinity page working at all (may because i am on a mac?). Dose any one know the actual old fashioned sums to work it out?

My set up.....
Tyre Size, 165/60X12
Drop Gear, Ratio 1:1
Gearbox type, Minispares (Clubman ratios CR/SC)
Final Drive Ratio, 3.211:1
TPM of Speedo, 1040

My Guess is about 5/17 but would like it as close as poss as it will be 95% on the road.

Any help much appreciated!

http://www.minifinity.com/distribution/vie...p?f=206&t=73640 http://www.guess-works.com/Gearbox/Technical/ratio.htm

Work it out manualy, you know how long a mile is, you have the tyre size, you have the final drive ratio, and the TPM for the speedo. The rest is inconsequential.

Divide the mile by the rolling circumferance of the tyre (rolling radius roughly 5mm shorter then the actual radius) then mutiply that by the final drive, then divide that by the TPM. This gives you the speedo gear ratio, you then need to find which pinion, and which spindle will give you the closest ratio.

Spindles available 5,6,and 7

Pinions available 15, 16, 17, and 18

I did have the Minifinity gear calculator and it was a very good program, but it was infected with WIN32:Vitro about a year and a half ago, so that was the end of that and the rest of the drive

Oh and Minifinity.com no longer exists, it is now minifinity.co.uk if you were ever that concerned

Edited by Sprocket on 12th Jan, 2010.

Top stuff sprocket! I am sure i could have worked this out if i thought a bit harder, 2 lazy for my own good!

i have never being on minifinity before and the way you boys slag it of dont think i ever will, just found that link on an old topic on hear.

thanks again i will get my calculator out need some coffie first bit early for pi lol

There's another good one here without going near Minifinity

http://www.tomsminisite.co.uk/speedo_calculator.php

Schrödinger's cat - so which one am I ???

Rod, yea tryed that one to he dosent list my final drive i dont think :(

Sprocket, are you saying the difrence in gearsets is inconsequential?
Tar

Yes, as the final drive is constant

Schrödinger's cat - so which one am I ???

He means his speedo turns per mile Rod

Ok some one fancy checking my maths.....?

Tyre dia 0.48m 48cm / 2.54 = 18.89/36 = 0.5249 yds Dia = Pi D = 1.649 yds

(yds per mile) 1760 / 1.649 = 1067 Revs/mile

X finad drive ratio = 1067 X 3.211 = 3426.137

/ TPM 1040 = 3.294

5/16.47

so i need 5/16 time to put the kettle on!