[Hiddenknife]

Hi folks!

I ve been searching alot on this topic weather you should pick OE tires for your BMW model or regular non OE tires. Interstingly i ve not yet found any conclusion on this matter if you should run OEM tires to avoid any potential xDrive issues or run normal non OEM tires because of the better price & comfort being non runflat. Nobody gives an clear answer why you should pick one over the other technically. Theoretically BMW approved tires have the same rolling circumference, being created specifically to meet the stringent low RC tolerances of xDrive.

Yesterday i found something very interesting. I compared two brand new tires one Pirelli Sottozero 3 (star marked) runflat and a regular Michelin Pilot Sport 4s non runflat of the same size, load rating and speed rating. 245/45/20 103V

In the photos attatched you can see the OE tire is slightly taller than the non OE one even if it has 0.5 mm less thread than the non OE tires. (8 for MPS4S and 7.5 for Pirelli)

I ve seen many people post around that if you mount tires based on the readings on the B pillar specs you are totally fine as long as it matches the exact tire size, load & speed ratings. But the question is, are they acutally the same? Obviously it seems they are not. Are we exposing ourselves to transfer case/xdrive issues? i dont know. Maybe we dont see an immediate effect on the drivetrain but maybe it stresses it s componets running non approved tires.

Making this post is not because i am an advocate of OEM tires but because i wanna see what othets think about this matter.

[Bc2005]

I’m not sure I understand your point, since actual measurement size differences between brands is common. It only seems significant if you plan to mount two different brands or types of tires on your car at the same time.

BMW wants all the tires to match diameters within about 2.0-2.5mm to keep the xDrive happy and not cause issues. If all the tires on the car are all the same brand, type and measured size, the actual diameter may be larger or smaller than OEM and it will not hurt the xDrive.

[slilley]

Long-time track and autocross driver here - so I've done a decent about of tire-related research over the years. You won't risk hurting xDrive unless you put on mis-matched tires, like different brands front and rear (unless they came staggered in size from the factory - but even then, I'd never put on a different brand or type of tire on one axle).

xDrive wants to see similar circumference on all wheels. I rotate my wheels every 10K to even out the wear (using a simple front-to-rear swap, not the more complicated front-crossover method that requires all four wheels off the ground).

Often, OE tires are some of the worst available when you look at Tire Rack ratings. My X5 came with Bridgestone Alenza Sport A/S tires, which are rated #32 out of 54 for my tire's type and size. I definitely won't be getting these tires again, although admittedly I personally have no complaints with them so far. The priority of the X5 is comfort, so the tire requirements aren't very stringent.

Those Michelin PS4S tires are awesome summer tires. I've had those on several of my "fun" cars, and may go back to them in the future. Right now I'm running Cup2's on my fun car. Great tires when they get heat in them (like at the track), but for the street, the PS4S is a much better all-around tire. I just wouldn't recommend the PS4S tire (or ANY summer tire) once the temps drop below 40F. In light snow or freezing rain, they are comically ineffective as tires! When I was much younger and naive, I thought I'd be OK on summer tires in the winter if I just drove extra slow. All it took was a couple flurries to prove that theory wrong!

[Jolbex]

True! I think the problem was with non star tyres having softer side wall which causes significant flattening of the diameter during extreme accelerations....leading to enormous stress of the transfer box. I also believe the earlier xdrive models were more prone to failure since almost every piece failed eventualy. Havent heard of such failures on newer models lately....

[RockCrusher]

What I gathered with my 230ix (and I assume the same is true of my M8) is using the BMW sanctioned (identified by the Star on the sidewall) tires of the size called for by BMW ensured the tire diameters would have the same wheel rotation speeds between the front and back tires.

I think no more than 1% was the allowable difference. But one has to be careful. When I asked at my local dealer was told 1% but when I pressed for something in black and white there was nothing forthcoming. Rather I was told the tech when the car was in for tires would look up what tires were suitable for the car and fit those tires.

If you find non BMW sanctioned tires (that don't have the Star) you must still be sure the tire sizes agree with what BMW calls for and also ensure tire diameters do not differ by more than what is permissible, assuming you get accurate info on this metric from BMW directly.

But even if you get the right diameter tires there is a risk the tires could prove to be subpar in terms of handling/braking/road feel/etc.

I've driven my other German sports cars hundreds of thousands of miles always fitted with factory sanctioned tires of the proper size -- the cars had staggered wheels/tires and one had an AWD system -- and regardless of the brand (Pirelli/Michelin or Continental/Bridgestone) -- I could not tell the difference between the tires. Road feel, handling, tire life, all were the same.

Oh there's more. This manufacturer did not sanction mixing brands of tires even if the tires were sanctioned. IOWs, I could not run Pirelli on the front axle and Michelin on the rear axle.

And even with the same brand of tires all the tires had to be of the same generation. The generations were labeled "N0", "N1", and so on. No mixing -- even on an axle basis -- of different generations of tires.

I have not put enough miles on my BMWs to have to replace tires yet but when the time comes I'll stick with BMW sanctioned (Star) tires.

[IanH]

1% is literally a rumor that is pervasive on this forum and the internet in general.

There is no hard and fast rule documented anywhere, and frankly it's unlikely that BMW or anyone actually knows since testing these types of things is highly impractical and near impossible.

Try your best to keep front and back tire diameters the same. If they are not the same you may see an issue or you may not.

It does seem that 1% or less is safe.

End of discussion, nobody can say ANYTHING more conclusively.

[reallymarkedup]

Originally Posted by IanH

End of discussion, nobody can say ANYTHING more conclusively.

I can conclusively say that this will not end the discussion.

[IanH]

Originally Posted by reallymarkedup

I can conclusively say that this will not end the discussion.

Just gotta get a bench mark down so that when the inevitable "wild speculation and fear mongering" posts follow they can be rebuked.

[Hiddenknife]

Originally Posted by RockCrusher

What I gathered with my 230ix (and I assume the same is true of my M8) is using the BMW sanctioned (identified by the Star on the sidewall) tires of the size called for by BMW ensured the tire diameters would have the same wheel rotation speeds between the front and back tires.

I think no more than 1% was the allowable difference. But one has to be careful. When I asked at my local dealer was told 1% but when I pressed for something in black and white there was nothing forthcoming. Rather I was told the tech when the car was in for tires would look up what tires were suitable for the car and fit those tires.

If you find non BMW sanctioned tires (that don't have the Star) you must still be sure the tire sizes agree with what BMW calls for and also ensure tire diameters do not differ by more than what is permissible, assuming you get accurate info on this metric from BMW directly.

But even if you get the right diameter tires there is a risk the tires could prove to be subpar in terms of handling/braking/road feel/etc.

I've driven my other German sports cars hundreds of thousands of miles always fitted with factory sanctioned tires of the proper size — the cars had staggered wheels/tires and one had an AWD system — and regardless of the brand (Pirelli/Michelin or Continental/Bridgestone) — I could not tell the difference between the tires. Road feel, handling, tire life, all were the same.

Oh there's more. This manufacturer did not sanction mixing brands of tires even if the tires were sanctioned. IOWs, I could not run Pirelli on the front axle and [...]

So from your experience staying with OEM tires is the way to go to "feel" the car as the creators intended, i m assuming. Look for example i ran the whole summer Michelin Pilot Sport 4s on an X4M40 and the car felt very loose, especially when cornering. It had grip but wasnt sharp and stable

[alex2364]

Originally Posted by IanH

1% is literally a rumor that is pervasive on this forum and the internet in general.

There is no hard and fast rule documented anywhere, and frankly it's unlikely that BMW or anyone actually knows since testing these types of things is highly impractical and near impossible.

Try your best to keep front and back tire diameters the same. If they are not the same you may see an issue or you may not.

It does seem that 1% or less is safe.

End of discussion, nobody can say ANYTHING more conclusively.

Try again. BMW has documented 2 mm or less in tread difference, which is less than 1%.

https://g20.bimmerpost.com/forums/sh...19&postcount=4

[IanH]

Originally Posted by alex2364

Try again. BMW has documented 2 mm or less in tread difference, which is less than 1%.

https://g20.bimmerpost.com/forums/sh...19&postcount=4

The OEM specs on at least the M240 ZTK, exceed this diameter recommendation. 5mm difference between 245/35/19 and 255/35/19

I would argue that this is regarding the use of old and new tires together and a CYA to force customers to buy new tires.

[DanG]

This is a very funny discussion. Lots of people have changed from runflats to non runflats with no problems on their all wheel drive BMWs. My brother-in-law has run Michelin CrossClimate SUVs on his X5 for the last 50K miles with no problems. Obviously they are not star spec but they are the same size as stock tires.

[RCM78]

Tyre Reviews did a non BMW Star PS4S vs BMW Star PS4S.
His opinion is the BMW OEM tires work better. No mention of Xdrive though since the car used for the test was an M

[smrtypants44]

Originally Posted by IanH

The OEM specs on at least the M240 ZTK, exceed this diameter recommendation. 5mm difference between 245/35/19 and 255/35/19

I would argue that this is regarding the use of old and new tires together and a CYA to force customers to buy new tires.

Yeah if BMW had such tight tolerances on xdrive then units would be failing all over the place just from manufacturing and wear variances.