Speedo drive ratios
Turbo Mini Forums

I have worked out the combinations I will need but I wondered if these drives are fully interchangable i.e can I use any pinion (5-7 teeth) with any drive (15-18 teeth)
Also I have 3 engines a metty turbo, a metty 1275 n/a and a mini city 998. strange thing is that they all have a 5 tooth pinion and 17 tooth drive. (well, the 2 that have drives do) with the different FD ratios I find that strange, Am I counting the teeth wrong?

website:- http://www.terryhunt.co.uk

Hi,
On the earlier Minis I believe the calibration factor was in the speedo head itself. However I'm not 100% sure on this!
Cheers,
Gavin :)

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Right, this could get complicated.

To find the right speedo drive ratio you need to know the final drive ratio, the turns per mile of the speedo (depends on which speedo you have, and that goes for ALL speedo types and ages) and the wheel size

Then use this program http://www.minifinity.com/index.php?name=U...req=getit&lid=4 (yes i know its minifinity, but the program is realy good) Input all the information and it will tell you the speedo drive ratio.

You then need to work out what combination of gear/ pinion gives the closest match to the given ratio. Theres enough combinations to get within 5% acuracy. BUT, be warned that there are some combinations that just dont work together, though most of the A+ gears ive had seem to be pretty much interchangeble with problems arising only with some of the older A gears. The spinldes are all the same, 5,6 and 7 teeth, the pinions can vary, ie, 2 different size 18 tooth.

Center smiths speedos pre 85 have the turns per mile one the face some where. The smiths and Nippon behind the wheel speedos 85 on and some others the turns per mile is moulded into the plastic coloured spindle in the speedo mechanism itself. This requires the removal of the mechanism from its housing.

Get the speedo ratio as close as poss, then if you must, have the speedo calibrated to get it almost dead acurate.

Hope this can help some one

Check this link out,

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

lots of info and a calculator, it may be similar to the minifinity one sprocket has posted?

Yup did all that, I was up till 3am running all the combinations for the 3 speedo's and 3 possible diffs I can use, I'm pretty sure I have the right numbers. I just wanted to make sure that any pinion will mesh correctly with any drive before I start looking for them and Looking at the calculators you posted It seems so..

I liked the calculator at http://rcmoc.org/bitsnbobs/coolstuff/Ratios.html as it includes actual and indicated speeds for each gear and rpm.Though It didnt actually have all the speedo's I have but if you know a bit of html you can save it to your computer and frig it for any speedo tpm.

What I find strange is why the turbo engine has a 5/17? and why the 89 mini city998 also has a 5/17 (though I didnt actually pull that one I was just peering down the hole...) maybe the Mini city actually has a different pinion and it just looks the same. Thinking about it in daylight It has to look the same or it would not mesh, I guess I'll have to pull it.

website:- http://www.terryhunt.co.uk

I pulled the drive out of the 998 engine and it is in fact a 7 tooth, ..... wonderful, with 165/60/12 wheels, a 3.2 diff, 17/7 speedo drive and my 1776 speedo I am within 2% Good enough...

website:- http://www.terryhunt.co.uk

OOPs..

1376 of course! I have so many numbers in my head now I can't type..

website:- http://www.terryhunt.co.uk