[M8fam]

Hello all,

I am awaiting delivery of my new '21 M240i xDrive with all season run flat tires. After reading online reviews of how bad the OEM run flats are, I'm thinking of just swapping them out right away for Michelin Pilot Sport All Season 4.

From my understanding, square setups are 7.5x18 all around? What would be an ideal setup for an xDrive? Should I go with 225/40ZR18 or with wider 235/40ZR18 tires?

[TrboMike]

235 will obviously give you more grip as it is wider, but the diameter of the tire will also be greater since you are not changing the aspect ratio of the tire (the middle number). Your 235 will be .3 inches greater in diameter, so the car will be .3 inches higher off the ground and your speedo will be off by 1mph. If you can live with that, its a good trade off for more grip.

Since all four tires will be the same size, xdrive and stability/abs systems wont be effected.

To keep the tire diameters statistically the same but have wider tires (more grip) you'd need wider rims. If you want to keep the OEM rims, 225 to 235 in the same aspect ratio is a good tradeoff to get more grip without much negative effects (speedo slightly off, car slightly taller which you may never notice).

[aerobod]

225/40-18 is the widest tyre that is certified by the tyre manufacturers to fit 7.5”x18” wheels.

[dradernh]

Originally Posted by M8fam

Should I go with 225/40ZR18 or with wider 235/40ZR18 tires?

Originally Posted by aerobod

225/40-18 is the widest tyre that is certified by the tyre manufacturers to fit 7.5”x18” wheels.

...as shown here in this snapshot from Tire Rack's site:

[Maynard]

Or keep the wheel/tire setup you have for winter, and get a set of 8" square wheels mounted w/ 225's - the wider wheel will give a bit better steering response and handling. The added 10mm of width for 235's won't be noticeable, but tauter sidewalls will. Especially good if you go with light wheels, as you'll also appreciate the lower unsprung weight (you could shave more than 4#/wheel fairly easily, which is quite noticeable).

[MasterFloody]

I can attest to the run flats not being good enough. Don't get me wrong, they aren't the worst thing I've been on, but if you drive spirited at all (in any weather) the run flats leave you a little less confident. I've only put about 10k miles on mine and I am ready for the swap too. I'm torn between the Conti DWS06's or the Mich Pilot A/S4's. Had the DWS's on another vehicle and they were AMAZING for the price. The A/S4's are fairly new while the A/S3 has a fan club. I might join you on the Mich's just for experience. Either way, I would stick with the OE size. I hear there are rubbing issues when going wider, and you can stagger them but then you can't rotate them.