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[ideliver]

I could really use some help.

2011 328 xdrive with 6MT. The stock rims were 17x8 ET 34 mounted with 225/25/17. I decided to get new rims as the originals were in bad shape (I purchased the car used). I went with ALZOR 040 staggered 18x8 ET35 and 18x9 ET38. I mounted 225/40/18 (rolling diameter of 25.1") and 255/35/188 (rolling diameter of 25"). The fronts were "stretched" and this was not intended. The rears look great and I chose the Pirelli PZero RFT

After a 1000 miles or so, the front tires created a lot of noise. I took the car to a indy that I have used for a long time. It's my son's car and he's moving about 150 miles away. We had all of the fluids changed (including the gear box and transfer case) and had them look at the front end.

They said the tires were cupped badly and that they were the wrong size. I purchased the tires from TR and this was their recommendation (as as best as I can tell, is the BMW OEM staggered sizes too). Regardless, they insisted that I needed new tires and mounted 245/40/18 with a rolling diameter of 25.7 and is 2.4% difference from the rears. Also, a slight amount of rubbing in the wheel well. To add insult to injury - they mounted Pirelli PZero ALL SEASONs on the front. The rears are summer tires.

Well, we drove the care 150 miles and noted that shifts from 2nd to 3rd resulted in some type of noise coming from the transmission or drive train somewhere. To me it sounds like a syncro. If 2nd gear is avoided, no problems.

I then decided to return home with the car and would take to the indy. After driving for a while, the noise was gone, only to return when the car sat overnight and then drove. It got me thinking. I took of the offending tires and put the winter tires and rims on - the drive train noise is gone - for now.

For good measure - I gave away the OEM take offs to a friend.

What should I do?

1. Go back to the OEM 17" square set up. I would need 4 new rims and tires.

2. Go to an 18" square setup. 225/40/18 would be the size I think. Do I need a 7.5" rim because the 8" rims look like shit with this tire.

3. Something else I'm not seeing?

4. Why did my 225/40/18 wear badly on 18x8 rims? Is this the wrong rim for that size tire?

Any help is appreciated.

The Pierlli does not have 235/40/18.

[andykrow]

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.

[ideliver]

Thank you. This is very helpful.

I looked at the stamping on the rims and they are 18x8". You could not lay the rim down on ground because the face would be touching the concrete - not the rubber. That's how stretched the Pirelli P Zero's 225/40s were on those rims.

[andykrow]

Maybe the Perilli's are particularly narrow in that width idk. Actual vs stated tread width varies a lot between manufacturers and between actual tire models.

If you think about it 225mm is 8.9 inches. That should not appear stretched on a 8" rim. Also, that's supposed to be a measure of tread width on the ground, not sidewall to sidewall.

[ideliver]

Measured rim width is 8" The rims are stamped 18x8. I am going to break them down and measure directly. It's all a mystery

https://www.tirerack.com/tires/tires...lar=Base+Model

[whyzee125]

I'd go to a square setup, something like 17x9 et30 all around or 18x9 et30. You could run a 245/40 or a 255/35 tire, it will look beefy but have decent clearance and no more x drive concerns.

[flapeo]

I have 225/40/18 on a 18x8.5 and its not stretched. Somethings wrong here

[ideliver]

Got the car back. Needed an alignment.

Put new 225/40s Pirelli P Zeros on the front. Here's a picture of the rears 255/35 on 18x9 and fronts on 18x8

[Cyril Sneer]

This is strange. On paper, everything is a correct size. I agree measuring the wheels and tires manually might show that one of the other is mis-sized. All size specs are available online. You shouldn't have to dismount the tires.

The bigger question is why did your Indy insist on ignoring the correct sizes and putting on tires that were a very obvious mismatch and possibly causing permanent damage to xdrive components...