8 replies to this topic

[Superleggo]

Hi

 

I have changed the wheels on my 1974 mini 1000 from 10" wheels to 12" items. I guess this will make the speedo read low. as the car is for my son I am keen the speedometer reads correctly

. 

What is the best way to recalibrate the speedo so it reads accurately. 

 

swap it for an item from at later / different car? Which one to retain the centre clock?

 

Can you swap the drive in the gear box for one with different ration. What ratio do I need?

 

Recalibrate the current speedo. Can this be done by DIY?

 

Thanks for the help- My mini knowledge is a few years out of date as I previously owned a 1974 mini in 1978! Now I have got another 1974 mini I guess it is in the blood!

[The Principal]

If you dont want to get your hands dirty give these guys a shout - http://www.speedycab...alibration.html

 

As explained in the link take a few measurements and send them the speedo

[Dan]

Wheel rim size doesn't make any difference to the speedo, it's the rolling diameter of the tyre that matters. Because you have to use a lower profile tyre with a 12" to be able to fit it into the body the difference between 10" and 12" is normally inside 2%. You'll get a bigger difference from having low tyre pressures! Because they tend to read over slightly from the factory anyway it may now be more accurate than it was. There are various comparisons you can make to test it, check against GPS (depending how accurate you think that might be), check against another car, have a passenger count phones on the motorway against the odometer etc.

[Guess-Works.com]

Assuming everything was standard, and working correctly, before you changed anything then the car should have 10" wheels, with a 3.4 final drive, a 1280 tpm speedo head ( number written just under the odometer ) and a 6/17 speedo worm/pinion drive.

 

Changing to 12" wheels and a different tyre profile does have a small effect...

 

using the calculator on my site will show you the difference and also suggest the correct replacement speedo drives. No need to muck about with the speedo itself.

 

http://www.guess-wor.../Tech/ratio.htm

 

If you plug in the right numbers it should suggest a 6/16 speedo worm/pinion so you just need to remove the 17 tooth pinion and replace with a 16.

 

And now for the gratuitous advertising....... http://www.guess-wor...play.htm?id=299

[mrmeds]

hi - ive just acquired  a 88 city e on 12 '' wheels that's had a central speedo with   1408 tpm  fitted. As far as i can see the  odometer is working fairly accurately but the speedo is 5-10 mph depending on the speed-   anyone got any ideas as to best way to fix this ?

ive had a fiddle on the guessworks site and it  says i need a SPD7/17  -  but being  a bit thick i'm not sure what to do with this nuggett of information !!!!!

 

help !

 

( sorry for jumping someone elses thread too ) !

[Spider]

The 7 / 17 are the speedo drive gears that you may need to change to in your gearbox or you may already have them as your odometer is right.

 

The Smith Speedo heads are adjustable for fine tuning that 5 - 10 that you are out, not sure on the Nikon units?

 

I'll see if I have a photo,,,,,

[GraemeC]

If it’s a centre speedo, it won’t be a Nippon

[Guess-Works.com]

If you're odometer is correct then your speedo calibration is out... the 1408 is the calibration for the odometer.. it sounds like your needle sweep has gone out of calibration and this can only be corrected by having the speedo head recalibrated...

Would be cheaper to find another speedo..

[mrmeds]

thanks for info- Will try and measure distance again over a greater distance- only did over 10 miles yesterday just to double check odo is accurate.

 

The speedo is a smiths by the way