That indy has it wrong I think. Stock staggered fitment with the M-sport Xdrive is front 18x8 et34 and rear 18x8.5 et37. Stock tire size for those rims is 225/40r18 front and 255/35r18. Don't know why your indy would say it's wrong. It's on my door jam lol.
BTW I run this with Michelin pilot AS4 and I don't think it's stretched at all... You might want to check your Alzor's as I've read reports of them getting shipped with the wrong sizes in the box.
I don't know what the consequences are for mismatched tire sizes but BMW says they are to be max 1% different. Seems reasonable that bad sounds could emanate from the drivetrain.
Regarding the cupping you likely need an alignment. Could have worn suspension components as well.
Personally I'm planning on a square setup once I wear out my current tires just so I can properly rotate them. 17 or 18x9. et30. 245/35r18 or 245/40r17. 17" can get you into some pretty lightweight setups.
|