G21 B3 Pirelli ALP Tyres

[Jonnywishbone]

Does anybody have a view on different brand tyres front vs rear, especially bearing in mind the reported sensitivity of the X-Drive system to tyre imbalances?

I ask because switching to MPS4S all round would require me to ditch the rears which have fewer than 2k on them. But I don't want Pirellis on the rear and Michelins on the front if it's going to cause a significant safety issue during normal driving or if it causes the AWD system to go on the fritz (degradation of the handling on the limit doesn't concern me).

[Rob Hardman UK]

Thanks very much. Rob

[Marc 76]

Does anybody have a view on different brand tyres front vs rear, especially bearing in mind the reported sensitivity of the X-Drive system to tyre imbalances?

I ask because switching to MPS4S all round would require me to ditch the rears which have fewer than 2k on them. But I don't want Pirellis on the rear and Michelins on the front if it's going to cause a significant safety issue during normal driving or if it causes the AWD system to go on the fritz (degradation of the handling on the limit doesn't concern me).

Sal, The thing with the Xdrive is the overall diameter of all four tyres has to be virtually identical (seemingly up to 3mm maximum difference is tolerated, or 2mm when Awd) so whatever you choose as a replacement has to be carefully considered size wise. Matching the sizes is further complicated by the BMW approved * marked products, which can be different dimensionally to the same size and make tyre that is not * marked. The tyre spec sheets found on the manufacturers websites generally list the standard tyre dimensions, not the manufacturer specific versions.
I've spent months chasing a niggly problem around my better halves 1 series Xdrive which runs a staggered factory set up. Calculating overall diameters from the nominal tyre sizes gives a difference front/rear of 8.5mm! (somewhat greater to the 2mm max difference allowed) Now i know that's not true- the difference is much less due to the actual diameters of the * marked tyres. However the rear tyre is still actually smaller from new, and the rears wear faster than the fronts so it doesnt take much tread wear on the rear for them to drop out of tolerance and start giving issues. I've now solved this problem by fitting same size * marked tyres all round and the car drives as good as ever, with the transfer box not having to work beyond it's capability to compensate for differing front/rear wheel speeds.

There is absolutely loads of internet chat about Xdive tolerances if you search, some good and some not so.
Some info i found which does appear to be directly from the BMW system is as follows:

Repair instruction
Notes and specifications for tyre / wheel exchange
3612... | REP-ALG-RAGRP36-3600_REIFENTAUSCH - V.6
ui-button
General:
•The tyre size, manufacturer and tyre tread must be the same on one axle
•To meet the BMW standards, the vehicle should be equipped with tyres from the same manufacturer and with the same tyre tread (tyres approved by BMW) on all 4 wheels
•The difference in tyre tread depth on one axle must not exceed 2 mm (control quality of suspension control systems and wheel alignment requirement)
•The tyres with the higher tread depths must be mounted on the rear axle
•The DOT age difference must not exceed 4 years
•The tyre pressure must be adjusted when the tyres are exchanged
•Wheel exchange between the axles
The wheels may be exchanged between axles to achieve even abrasion. However, BMW does not recommend switching the front wheels to the rear or vice-versa.
The wheel exchange may lead to the following customer complaints:

complaints regarding acoustics

Risk of increased lane groove sensitivity
Compliance with the following requirements is required when exchanging wheels between the axles:

Assess the wear pattern

The tread difference between the front and rear wheels must not exceed a maximum of 2-3 mm

Exchange the wheels between the axles every 5000 Km
**Additionally for all-wheel drive vehicles: **
•The tyre size, manufacturer and tyre tread must be identical on all wheels; different tyre sizes between front and rear axles are only permissible if mixed tyres are fitted.
•The tyre tread difference between tyres in all wheel positions must not exceed 2 mm (normal quality of the wheel control systems and wheel alignment requirement)
XXXXXX XXXXXXX

So all that said, if i were to change tyre manufacturer on an Xdrive i'd want to be absolutely 100% confident of the actual sizes (overall diameters) front/rear if staggered.
And i'd only use * marked products on a BMW.

Did earlier models of your car run Michelins on Xdrive and in the same size as your Pirellis?
I guess not as that would make life too easy!

[Jonnywishbone]

Thanks for the very comprehensive reply Marc, I appreciate it. The B3 is my first X-Drive and my awareness of some of the online chatter about its sensitivity to tyres is what prompted the question.

Your technical knowledge here exceeds mine but you’ve reinforced the side of the fence I was leaning towards anyway, which is to stick with the same tyres all round and more specifically OEM.

I’ll make a decision about changing to Michelins when I have to change all four, given the (increasingly forlorn) assumption I don’t have another sodding puncture in the meantime!

[Marc 76]

No problem, as i say i have been looking around this for a while now so its all fresh in my mind.

From what i've read It seems when people go to BMW with the issue under warranty the usual course of action is for them to advise the customer to replace all 4 tyres, regardless that they may have many 1000's of miles left in them. That usually solves the issue but if it doesnt BMW have then been know to change the transfer box.

If you have a square set up (4 same size wheels and tyres), it should not be a problem to simply fit four new (*) tyres of any manufacturer but the issue arises with staggered set ups and different size front / rear tyres. It's much harder to match the diameters within the tight tolerance permitted so the easiest and most foolproof thing is to stay with what BMW or Alpina prescribe for the specific model.

As i've previously mentioned though, i might have a problem with that if it was Pirelli because of poor previous experience!

[Grumpyjohn1957]

Says it all Marc.
Any one whose interested and not already aware, have a look at tyre size.com (a great resource).
Stuck my tyre sizes into their comparator, results below.

Tyre Size.PNG (22.62 KiB) Viewed 658 times

Tyre Size 2.PNG (181.71 KiB) Viewed 658 times

[Marc 76]

Says it all Marc.
Any one whose interested and not already aware, have a look at tyre size.com (a great resource).
Stuck my tyre sizes into their comparator, results below.

That is indeed a great resource John, although i'm pretty confident it does the calculation from the nominal tyre size.

Yours shows a 6mm diameter difference, the 1 series i was having problems with shows an 8mm difference when calculated from nominal sizes, but BMW say 2mm max difference between front / rear on Xdrive vehicles. I know the actual difference between my own (*) marked tyres wasnt as much as the 8mm figure which is why i think that manufacturer approved tyres (*) have marginally different actual sizes to the nominal.
Making selection to the BMW tolerance extremely tricky, unless of course you simply stick to the prescribed rubber!

[Hawmaws]

Hi Guys,

To add to this interesting subject.

On my G21, I went through the Pirelli rears in under 10000 miles. At the time I couldn’t find any replacements, so I fitted Michelins. Which i prefer, if I’m honest.

Car has now done 33,000 and both front Pirellis and rear Michelins look as if they have worn evenly and are maybe a couple of months away from replacement.

I think I will replace with Michelins all round.

[Rob Hardman UK]

Thanks for sharing. rob

[big blue]

I think I will replace with Michelins all round.

Me too I will be doing this as an alternative. We will see how it goes.

[Metrics]

Interesting thread. I find it v odd that the xDrive cam be so sensitive that only OE marked tyres can be used?

Michelin tyres are quality in my experience - are we really thinking that a star marked Pilot 4S will have a different rolling circumference to a non start marked 4S?

Also, the rear biased nature of xDrive on the BMW and particularly ALPINA (even more rear biased from my understanding) means the rears are used up a lot faster than fronts, so the front to rear difference in rolling circumference could be quite large.

I'm planning on switching from P Zero ALP to MPS4S, if this doesn't cause drivetrain issues. I've been v disappointed with the P Zero performance.

[Jonnywishbone]

Had both my fronts changed (OEM Pirellis) per my earlier post with a bulge in the NSF and on removing the (what I thought was a perfectly good) OSF it had a deep, long gash on the inside shoulder which was waiting to give up the ghost any time. That makes 5 new tyres (4 of which were either undrivable or would be an MOT fail) in the space of a year and about 4K miles. I would still opt for the Classics if speccing another one, but that’s because I’m a tart. The 30 profile 20” tyres are not really compatible with crap road surfaces. And I’m assuming that’s nothing to do with the Pirelli construction.

Also, the rear biased nature of xDrive on the BMW and particularly ALPINA (even more rear biased from my understanding) means the rears are used up a lot faster than fronts, so the front to rear difference in rolling circumference could be quite large.

I don’t have a reference to hand and it’s possible my recollection is faulty, but from the research I did prior to buying I recall that counterintuitively, the B3 is less rear biased than the donor M340i.

Edited to add the relevant reference 6th para down.

[big blue]

I'm planning on switching from P Zero ALP to MPS4S, if this doesn't cause drivetrain issues. I've been v disappointed with the P Zero performance.

Agree with this one on the performance and I have just done the switch to MPS so will see how they get on.

[andy-integrale]

Found this quite interesting. Michelin PS4s OEM v Non OEM for BMW M.

https://youtu.be/COA630Juf_U

[Hawmaws]

I made the change to 4x mps4s on Friday.

Initial impressions are very positive. A slight ‘brittleness’ in the ride has gone and the car feels much more resolved and keyed into the road. I’ve found myself moving away from ‘comfort’ much more often, even in town.

I’m on 19s, but I can still feel a discernible improvement.