[JNW1]

Following a puncture I replaced the original equipment Bridgestone run-flats with a set of conventional Goodyear AS2's at about 22k miles. I've been very happy with the Goodyears and, 36k miles later, all four tyres still have about 4mm of tread left (which I think is pretty good!). However, just been washing the car this morning and, in the course of checking the tyres, I've spotted that the off-side front is through to the canvas on part of the sidewall. I had noticed the tyre in question seemed to be wearing a bit on the sidewall and it was in my mind to have an alignment check as the last time they were done was when this set of tyres was fitted; however, events have overtaken me and this tyre needs replacing (like now!).

Bearing in mind the tread left if it was an S-Drive I'd put probably two new tyres on the back and swap the best two of the remaining three onto the front. However, with an X-Drive am I right in thinking you shouldn't mix part worn tyres and new tyres even on different axles? If the part-worn tyres had, say, 6mm left I might risk it but given they're all at least half worn I'm thinking I ought to bite the bullet and change the full set; is that the right approach or am I being over cautious?

[TomJ79]

If you’re able to, I’d replace the full set just because it’s nice to have new boots all round. Ideally don’t mix but I had to have two new rears (non xdrive) so just match across the axles. Can’t see that having xdrive would make it any different. As it happens, I got a sidewall bulge and had to replace the right rear so now I have 3 Pilot Sport 4S’s and one SS. Not ideal but can’t afford to replace the SS this month! So it will wait...it’s fine for the time being.

[JNW1]

Originally Posted by TomJ79

If you’re able to, I’d replace the full set just because it’s nice to have new boots all round. Ideally don’t mix but I had to have two new rears (non xdrive) so just match across the axles. Can’t see that having xdrive would make it any different. As it happens, I got a sidewall bulge and had to replace the right rear so now I have 3 Pilot Sport 4S’s and one SS. Not ideal but can’t afford to replace the SS this month! So it will wait...it’s fine for the time being.

I would never mix a new tyre with a well worn one on the same axle but something sticks in my mind that the transfer box on X-Drives doesn't like tyres with significantly different amounts of wear front to rear either? That being the case two new tyres on one axle and two half-worn ones on the other would also be a no-no but I might be wrong.....

[lethbridge]

I wouldn't worry having a part worn and new mix front to rear (I've done many miles like that with no issues). You are correct that the transfer box is fussy so you certainly can't put different size diameters front to rear but BMW allow for the situation you are in. In terms of warranty if the box had an issue and BMW were to get picky it would be about you running non approved * marked tyres and not about different amounts of wear. In short you are fine just to change fronts and definitely worth getting a full alignment check - what you have reported is fairly normal if you don't keep runflats inflated at or above the specified value but on non runflats you shouldn't see that sort of uneven wear...

[rossm]

You shouldn't really have mismatched wear on the same axle for the simple reason is that deeper tread will clear more water and risk of aquaplaning into a spin is severely increased

[JNW1]

Originally Posted by lethbridge

I wouldn't worry having a part worn and new mix front to rear (I've done many miles like that with no issues). You are correct that the transfer box is fussy so you certainly can't put different size diameters front to rear but BMW allow for the situation you are in. In terms of warranty if the box had an issue and BMW were to get picky it would be about you running non approved * marked tyres and not about different amounts of wear. In short you are fine just to change fronts and definitely worth getting a full alignment check - what you have reported is fairly normal if you don't keep runflats inflated at or above the specified value but on non runflats you shouldn't see that sort of uneven wear...

Thanks for that!

Given the tyre profile is different front to rear there must be a slight difference in rolling circumference even when all the tyres have the same tread so, that being the case, I'm not so sure how much difference 4mm of tread will make? Guess I could just try replacing two and if I get any strange noises from the transfer box replace the other two as well; however, feels like belt and braces is probably to do all four, especially as I'm pretty sure I'll be keeping for the car for another couple of years!

The full alignment check is an absolute given regardless - must be something wrong to produce the strange wear pattern which has caused this problem!

[lethbridge]

Originally Posted by JNW1

Thanks for that!

Given the tyre profile is different front to rear there must be a slight difference in rolling circumference even when all the tyres have the same tread so, that being the case, I'm not so sure how much difference 4mm of tread will make? Guess I could just try replacing two and if I get any strange noises from the transfer box replace the other two as well; however, feels like belt and braces is probably to do all four, especially as I'm pretty sure I'll be keeping for the car for another couple of years!

The full alignment check is an absolute given regardless - must be something wrong to produce the strange wear pattern which has caused this problem!

Should be the same diameter front and rear - what tyre sizes have you got - I assumed from you mentioning swapping front to rear that you don't have a staggered setup and therefore the profile should be the same or you will be running into issues...

[JNW1]

Originally Posted by lethbridge

Should be the same diameter front and rear - what tyre sizes have you got - I assumed from you mentioning swapping front to rear that you don't have a staggered setup and therefore the profile should be the same or you will be running into issues...

Sorry, my fault for causing confusion there! The wheels are the same diameter all round (18") but actually even with RWD I couldn't swap front to rear as the fronts are 225/45 and the rears are 255/40!

My options are therefore to either replace the front pair with two new tyres (and in that scenario I'd stick with AS2's to match what's on the back) or replace all four (in which case I could look at something different given the world has probably moved on since the AS2's were introduced).

[lethbridge]

In your position I would just replace the fronts... BTW they will be the same profile front to rear... The profile figure relates to the % of the width so 40% of 255mm is 102mm; 45% of 225mm is 101.25mm - so 0.75mm difference in tyre wall height and therefore 1.5mm difference in the diameter