20 replies to this topic

[mattrsa]

Hi All 

 

The odometer in mini seems to be counting incorrectly. 

 

I have an 88 mayfair which was on 12 inch wheels but I have now put 10 inch wheels on it. I have not really been paying much attention to the odometer but I wanted to calculate my MPG the other day on a little run so I decided to make a note of the milage. 

On closer inspection I noticed that the odomoter is logging 1 mile, for every 0.6 miles I travel according to google maps. I know there is a slight over size difference from 12 to 10's but surely 0.4 of a mile out is not correct. 
 

Any ideas. The care in insurance for 2000 miles a year so I would like the odometer to provide and accurate measure. 

 

thanks in advance. 

[sonscar]

You will have to fit the original tyres and wheels for an easy fix.Other fixes are to calculate the speedo gears needed and change them or fit and calibrate an electronic speedo.So; easy,labour intensive,costly in that order.Have fun,Steve..

[nicklouse]

Go to Guessworks web page and see the info on speedos. Then work out what you have. And change accordingly. .

[mattrsa]

thanks for the replies. 

 

I realise that the change in wheel/tyre combination would make a difference but based on my calculatation there is only about a 5% difference in overall diameter which surely would not result in such a massive difference (0.4 miles)

 

If it going to involve lots of fiddling I will just put up with it to be honest, might have to uop my insurance to 3000 miles though. 

 

[sonscar]

Beware that your indicated speed will be incorrect.Changing the speedo gears is fiddly but doable if you have a spare day.It involves some dismantling,Steve..

[Gilles1000]

How accurate was the setup with the 12s?

This may also be not accurate from the matching speedo/wheels/pinion...

[mattrsa]

How accurate was the setup with the 12s?

This may also be not accurate from the matching speedo/wheels/pinion...

 I don't know but I presume it was much closer as currently there is a 40% discrepancy. I expected that due to the slight change in size there might be a 10-15% difference. 

[Ethel]

All Mini tyres give pretty much the same same rolling circumference, much closer than that anyway. It's almost as if it's reading in kilometres instead of miles...

[1314cc]

Had to change my speedo gears. Fair bit of dismantling but really is quite straightforward.
I also used Guessworks to get the correct set-up as mentioned already

Edited by 1314cc, 14 April 2022 - 01:43 PM.

[mattrsa]

All Mini tyres give pretty much the same same rolling circumference, much closer than that anyway. It's almost as if it's reading in kilometres instead of miles...

Yes I did think it was going KM initially but the clocks are clearly labelled MPH and they dont appear to have been dismantled or changed in any way. 

[Ethel]

The faces do come off, so it's not impossible somebody has  done some swapping. If the speedo drive gears in the gearbox had been mucked up it'd also show on the speedo so that doesn't seem likely. The reduction gear operates a little pawl on a ratchet wheel to advance the number drums. I suppose  it's possible it's worn so it skips teeth, but that would be erratic and more likely to stop it altogether.

[Spider]

There's little difference in the rolling diameter of the wheels between 10's and 12's though just enough to be noticeable. It does sound to me like there's an underlying error here, it's not just the change of wheels to be that far off.

 

Sounds like the Speedo Drive Gears are incorrect for the Final Drive and Wheel combination.

I usually calculate the Drive Ratios old school on paper. You'll need to know what the TPM (turns per Mile) of the speedo is and you can look up on line for most tyres, the Turns per Mile they will do.

As the Odometer is positively engaged, via various gears, to the wheels if you are wanting to do a Speedo Calibration, you first need to get this part sorted out. Once the Odometer is right, the Speedo, with is magnetically coupled, can then be adjusted. If the Odometer isn't first sorted, the Speedo usually won't read linear.

[Compdoc]

There are plenty of apps on "play store" for your phone that will give you accurate speed and distance using the phones GPS.

[Steam]

Firstly GPS and Google are not as accurate as the suppliers would like you to think.
Also it is not unknown for the speedo drive squares to round off somewhat giving false readings due to slippage.

[Homersimpson]

Is the speedo itself accurate?  I assume that its not 40% out otherwise you would have noticed before? 

 

If the speedo is fine and the odometer is not recording correctly then its probably an internal fault in the speedo or someone has been playing with it and fitted a km odometer to a MPH speedo.