5 replies to this topic

[ODD1991]

Model:Ritz
Year:1985
Description of problem (please be as in depth as possible):

hi, i was thinking of getting the 12"-10" wheel conversion on my mini ritz.

i was wondering if it would effect the accuracy of the speedo?

also if i put a mk1 or mk2 speedo in my car would it be accurate due to the fact they were designed for 10 inch wheels?

thanks in advance.

Any non-standard parts that might be involved with the problem?

[Ethel]

The speedo is driven by the end of the mainshaft so is effected by the final drive gearing & the tyre circumference. There are also different speedo drive gear ratios. Most Mini wheel/tyre combinations are pretty close to one another to only make a small difference. See Guessworks site for more info.

[Stevie W]

Hi,

Going from 12" wheels to 10" will affect the speedo reading.

Because the wheels will have to turn faster for a given road speed, your original speedo will read high.

Early MkI, II or III speedos were all set up for 10" wheels but the speedo drive ratios differed to cater for different final drives.

I think Guessworks on here has a calculator to tell you how far out your speedo will be for a given wheel diameter, final drive and speedo gear ratio.

Hope this helps!

Steve.

[Guess-Works.com]

Yes, there's about a 6% reduction in rolling radius from 12/13" tyre to the 10" tyre.

I have an ad' on ebay which gives a simplified table of the drive combinations...

http://cgi.ebay.co.u...em=150404747704

The Mini Ritz, as standard, has a 3.1 final drive with 7/17 speedo drive and a 1242 (90mph) Nippon Seike speedometer and reads slightly fast (as most speedo's do), changing to 10" wheels you will need to change the speedo drive to a 6/16 for the speedo to remain accurate, otherwise it will be reading will be fast.

[ODD1991]

Yes, there's about a 6% reduction in rolling radius from 12/13" tyre to the 10" tyre.

I have an ad' on ebay which gives a simplified table of the drive combinations...

http://cgi.ebay.co.u...em=150404747704

The Mini Ritz, as standard, has a 3.1 final drive with 7/17 speedo drive and a 1242 (90mph) Nippon Seike speedometer and reads slightly fast (as most speedo's do), changing to 10" wheels you will need to change the speedo drive to a 6/16 for the speedo to remain accurate, otherwise it will be reading will be fast.

thanks everybody, the info is great.

i got a question for guessworks. what if i get the old tyle centre speedo with the guages either side? what affect would it have then?

thanks again

[Guess-Works.com]

It would have an effect because they run a different TPM (turns per mile), but what effect would depend on the TPM os the central speedo, they vary even more than the Nippon Seike, you need to run through the calculations to get what's right.

Edited by Guess-Works.com, 18 January 2010 - 08:11 AM.