Probably your best bet is to get someone like Speedy Cables to re-calibrate the speedo head – I had this done for my Mini-based kit car, you just have to tell them how many turns of the cable there are for a certain number of turns of the wheel, then they sort it all out for you.

Rob

Edit – totally missed the coincidence of their company name and your username!

Edited By Grindstone Cowboy on 28/09/2023 18:12:50

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Just a ‘calibration orientated’ thought …

Have you checked that it also reads 50kph at a GPS speed of 40kph ?

Not sure what species of Speedo the early Mini used

MichaelG.

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Edit: __ I strongly suspect that they used ‘Magnetic’ speedos [at least on all but the exotic models] … but I stand to be corrected

Edited By Michael Gilligan on 28/09/2023 18:54:51

So either the different speedo drives had different cases, or it was done by tooth-sums. Different tooth-counts on each wheel but all adding to the same sum. Would that work?

Assuming 4th gear is 1:1 ratio stick it in gear, mark the tyre with chalk, take the plugs out and rotate the flywheel 1 rev and see what the wheel rotations are. That will give you the final drive ratio of your box.

That said all you really need to do is track down the correct gear set for your car and fit it.

[Speedy] Bob

This looks very useful: **LINK**

https://www.classicminidiy.com/technical/gearing

MichaelG.

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Edit: __ See also the first two items on the side menu here:

http://www.guess-works.com/Tech/ratio.htm

Edited By Michael Gilligan on 29/09/2023 04:59:03

Bob,

A corrector gear box can be fitted between two speedo cables and Speedy cables or Thomas Richfield could advise or you could make one yourself. Suitable range of small gear available from RS. You could put a different scale on the speedo but be very careful not to interfere with the needle. The only problem is that the odometer will not read correctly and I always find that a pain. Don't worry about the MOT as there is no requirement for it to be calibrated. However, it does have to read correctly within certain percentages and it is a pain if it does not.

Speedy Cables can probably make the ododmeter read correctly. They can also zero the mileage if you have no confidence that anything like the correct mileage is being shown. It is quite fun to know how many miles YOU have driven it the vehicle in total, especially if you have overhauled it.

John

Not sure the Mini has an excentric bush. Due to the geometry of a worm and helix they can accomodate a tooth or two ratio range by adhusting the diameter and tooth shape. It changes the amount of engagement but as there is little power transmission in a spedo drive that is acceptable.

Don't know about the French test but in the UK the MOT only reqiures the speedometer to work. Assuming it is a regular annual test not a one of for approval after modification etc like the SVA in YK. There is no accuracy test. The construction rules say the speedometer must be accurate to -0 +10% when new. It also has to be "independant" so you can't use GPS.

IF accuracy is a requirement but it is over-reading can you just put a label on the speedos saying it over-reads by 20kph?

If you are of an electronics bent you could add a digital speedometer. There are plenty of RPM meter (same thing different calibration) designs and even modules out there. If the back of the speedo is plastic you can often pickup a signal from the rotating magnet inside using a coil attached to the outside.

Robert.

On well …

MichaelG.

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Sorry … that should have read Oh well …