16 replies to this topic

[Dev20]

Hi I've got a '92 british classic open with a metro engine. It's got 155/70/R12 tyres on at the mo, and never thought anything of it. However, apparently they aren't standard for a mini, but are for a metro! When I next get some new tyres should I go for 145/70/R12 to keep it standard? Would this also help with the speedo being more accurate, at the minute it's off by about 10~15, I'm assuming the speedo cable gear wasnt changed when the engine was.

[MRA]

10~15 what ? % or mph ??

[Dev20]

10~15 what ? % or mph ??

Sorry, yes mph. It does rest at 0mph so it's not a simple case of moving the needle down.

[MRA]

ok, but is that at 30 mph (50% error) or at 300mph (5% error) ?

It is a little high, however most cars read high by about 10%

Edited by mra-minis.co.uk, 14 December 2010 - 01:32 PM.

[Dev20]

It's more like at 20mph it reads 10, at 30mph it reads 20, at 50mph it reads approx 43.

The chap i bought the car off told me the correct gear change for the speedo cable hadn't been installed during the engine change. But I'm just enquiring whether the tyre size can have such a significant difference and if I should convert them back to 145/70/R12??

[MRA]

how it works.....

The width in mm's the next number (70) is the percentage of the width deep, ie 70% of 145 is..... times by 2 and add it to the wheel diameter.

use 25.4mm per 1"

The error will be the percentage difference in diameter.

Edited by mra-minis.co.uk, 14 December 2010 - 04:23 PM.

[Dev20]

So 145/70/R12 has a height of = 507.8mm
and 155/70/R12 has a height of = 521.8mm

Therefore there's a difference of = 14mm

I've known mini's to be fitted with either 145 or 165 tyres but never 155. In conclusion, is this something i need to address or can just be ignored?

Thanks mra!

[MRA]

its about 3% difference....

155 70 12" used to be a common mod

[AVV IT]

Forgetting speedo calibration for a minute, if you do decide to change tyres then I really wouldn't bother putting standard 145's back on as the handling is absolutely awful on them. Opt for a decent set of 165's instead, as the extra tread width makes a massive difference to handling and also helps with braking too!!

[Bungle]

as above if you have the standard 4.5x12 wheels go for a 165 tyre

you might need a small spacer on the rear for the tyre to clear the shocks

[Guess-Works.com]

Think the key here regarding the speedo is the comment that the engines been replaced.... replaced with what is the question...

[MRA]

Der an engine .....

Oh you mean which engine and what spec etc ...

To be a little picky, the engine won't have an effect on the speedo, only the gearbox will do that....

It als obegs the question how do you know that your speedo is giving the wrong reading ?

[xBR4DLEY]

Had 155/70/12s aswell , gonna put on some 165s when I need to though

[Dev20]

Der an engine .....

Oh you mean which engine and what spec etc ...

To be a little picky, the engine won't have an effect on the speedo, only the gearbox will do that....

It als obegs the question how do you know that your speedo is giving the wrong reading ?

I believe the brittish open classics rolled out the factory with 1275 cooper engines, however it was changed to a metro 1275 with HIF44.

The guy who I bought it from told me about the change and the fact that the speedo gearing wasn't quite right. And also when i've got my sat nav plugged in, it is roughly 10mph out.

[AVV IT]

And also when i've got my sat nav plugged in, it is roughly 10mph out.

My Sat Nav is about 10mph out in comparison to whatever car I put it in, I'm not sure if this is an example of how inaccurate all speedos are or just how inaccurate Sat Nav is???