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      01-10-2021, 04:31 AM   #3
mr_lab_rat
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Drives: 2017 M2, 2018 X1
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Quote:
Originally Posted by MJE60 View Post
Hi
As you probably know, Front tyres/tires on F48 will normally wear quickest, the Xdrive system on the X1 (unlike higher range models) is predominantly front wheel drive with rear drive only used when traction is lost on front tyres or in severe stability situations (when esp engages). On my F48 2.0d xdrive the difference in front/rear wear was fairly small with front wear about 1mm-1.5mm greater after approx 12k miles however more powerful cars driven more aggressively would probably see a greater difference. Road condition affect rate of wear also.

Regarding on which axle to place the newer tyres, , the recommendation by most car and tyre manufacturers is to have tyres with better tread and therefore (in majority of driving condition) better grip on the rear axle. The reason is that for most drivers it is very much easier to manage/recover the loss of front grip than the loss of rear griip. On front engine cars there is usually also more weight on the front tyres so giving slightly better grip/traction. For these reasons many, including myself prefer to leave front tyres with greater wear in place despite knowing they will wear faster. For predominantly rear wheel drive cars like x3 it is an easier call to put higher tread on the rear. Many owners believe the best management option is to routinely rotate tyres front/rear so that wear is kept even, I can support this provided the difference in wear is never allowed to develop and this means discipline and very regular swaps. I normally always replace 2 tyres at once (putting best tread on the rear) and never let tread fall below 3mm in summer, slightly more in winter. If anyone doubts the manufacturer recommendation for best tires on the rear then look it up by also note than in many countries, including the U.K, you will find most tyre shops refusing to put new/better tyres on the front axle.

With regard to the “haldex” system coping with 5mm diameter difference in front to rear diameter, the answer is mechanically it can easily cope. Due to stearing action the front tyres will normally rotate at different rates to the rear when turning a corner anyway. The rear tires on an X1 are normally pulled along, there is no viscous coupling (used on some cheap part-time 4x4 system) which would be put under constant strain by different rotation rates, the haldex is a small auto clutch and it only engages drive to rear wheels when the brain/electronics sense front tyres slipping (or ESP kicks in). A difference of 5mm diameter (so 2.5mm tread wear between front and rear) is IMO not a safety concern although, I repeat that especially on front wheel drive cars (and the F48 is a front wheel drive /part time rear drive) it is recommended to always have best tread on rear wheels.

On another note, one of the reason I do not like run-flat tyres is it is almost impossible to get them repaired in many countries (for example Pirelli say they can never be repaired because of unseen damage caused when running flat, most other manufacturers have strict rules about repairs, often only once). in many countries tire shops just refuse, quoting liability as the reason. Having to replace 2 or 4 tyres because one has had a puncture becomes an expensive experience. The alternative is to put a new tyre on the same axle as a worn tyre which is not advisable if wear is more than a mm. I think this a bigger issue than differences In front/rear wear. I kept a tire plug-type repair kit in my X1 and decided to repair and try to never drive on a flat run-flat. Luckily I never not a puncture on the run-flats and the kit now sits in my new car with ordinary tires.
Thank you for such detailed reply. I'm also seeing very similar wear between the front and rear with maybe slightly faster wear on the fronts.
I am aware of the recommendation to put better tires on the rear axle but with 9.5mm tread on the new tire and 7mm on old I'm not too worried about lack of grip. Also my other car is an M2 so I'm quite familiar with oversteer
I was mostly worried about the AWD.
Thanks again.
Appreciate 1
MJE60678.00