Changing tyre size, will it upset xDrive?

[votchy]

Have had new tyres fitted to the front and have gone away from run flats as have seen many posts suggesting this. the rear tyres will soon be up for changing now and unfortunately I cannot find the size required to match the front. The rears are 255/40r18 and the fronts are Dunlop SP Sport 01, these are only available in 245/40r18  or 255/45r18. Can I fit either of these so I have 4 of the same tyre or will the change in size adversely effect the xDrive system? Have never changed tyre size from original on any of my previous cars so am not aware if I can or cannot and this is the first bimmer and first awd I have had so was wondering if fitting different sized tyres would cause issues.

[Bimmer Owners' Club]

I would definitely try to keep the rolling diameter of the tyres the same all round the car, width isn't a problem though

[votchy]

Rolling diameters of front and rears are different as standard, wondering if upsetting this known difference would cause issues although I guess it may not as there are 3 different wheel options as standard.

[Moff]

What does it say in the handbook?

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Mikeyp @ TMS Motorsport
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