Hello,

I was just looking at the mot history of a Mk 2_ superb 4wd and in 2022 it was noted it failed due to different size tyres on the front axle.  There is a period of a maximum of 2100 miles between this and the previous mot so assuming the 2021 mot inspection was decent this would be the maximum miles this would have been. What is the likely outcome of this and would there be damage or premature wear to the 4wd components?

Thank you

M

None.

 

The different sized tyres may well have the same or very close rolling diameter.

3 hours ago, J.R. said:

None.

 

The different sized tyres may well have the same or very close rolling diameter.

^This. The differential will handle the difference in speed. It wouldn't be great for handling though.

Thank you.

m

 

On 11/07/2023 at 01:40, MarkyD said:

Hello,

I was just looking at the mot history of a Mk 2_ superb 4wd and in 2022 it was noted it failed due to different size tyres on the front axle.  There is a period of a maximum of 2100 miles between this and the previous mot so assuming the 2021 mot inspection was decent this would be the maximum miles this would have been. What is the likely outcome of this and would there be damage or premature wear to the 4wd components?

Without knowing the exact tire dimensions that the car was on, this question can never be answered.

@MarkyDWas that different sized tyres on the front and at the driver / passenger side.

 

A different size front and rear is not a MOT fail in the UK.

Otherwise there would be lots of BMW, Porsche, Audi and many others failing.

Bigger on the front not an issue either, anymore than on the rear.

Different size tyres on the same axle is an MOT failure, Different size tyres front/rear is not a failure or an advisory. I could be that the spare wheel of a different size was fitted for a short period due to a puncture, that would still warrant an MOT failure.

 

Different rolling diameter will mean the diff has to work a bit harder and it might cause damage depending on how much the difference in rolling diameter is, how long and how the car was driven.  If I was really bothered I might change the transmission oil as a precaution, but wouldn't lose sleep over it. 

 

 

Edited 15 July, 20232 yr by CzechPassat

Yes there were 2 different sizes on the front axle ie driver and passenger were different sizes.

So the most likely scenario is that the spare wheel of a different size was fitted for a while due to a puncture.

On 15/07/2023 at 12:18, CzechPassat said:

Different rolling diameter will mean the diff has to work a bit harder and it might cause damage depending on how much the difference in rolling diameter is, how long and how the car was driven.  If I was really bothered I might change the transmission oil as a precaution, but wouldn't lose sleep over it.

Problem is that we still don't know whether the rolling diameters of the tires were in fact different.

After all, the circumferences of 205/55R16, 225/45R17 and 225/40R18 are all almost identical, so mixing these dimensions will not lead to premature wear of drive components.

 

So unless @MarkyD answers my previous question above (regarding the exact mounted tire dimensions), answering his original question is impossible.

Edited 16 July, 20232 yr by andrehj

I think the answer is that on the probability that someone fitted the spare for a limited period of time it’s unlikely to have caused any problem and as this was picked up from a previous mot the current owner won’t have any further details