Rim widths

I'm getting ready to buy some R-S4's, but for practical reasons my rim widths will end up sitting on the minimum recommendation. These would just for driving to and at High Plains Raceway here in Colorado. I suppose my question is, do I really need to replace the rims? My car will also be somewhat camber challenged with only -1.5 in front and 2.0 in back.

Can you add more details? Not sure what you're asking really. Is this for M3 or the 330i in your profile?

TboneS54 wrote

Can you add more details? Not sure what you're asking really. Is this for M3 or the 330i in your profile?

I'll come clean. I saw a previous post that convinced me that this group is tech focused, including tires for track days. I'm bombing this list even though I don't have an M3. It's more of a general question for track days posed to knowledge drivers. I know autocrossing with SCCA we weren't allowed to change rim width, but we'd still mount wider tires and go faster. I guess I'm not too uncomfortable with using any rim width that is in the recommended range for a particular tire, but will there end up being more wear along the outer edge? General opinions on any impact of different rim widths on track performance are welcome. The tires will be on an extra set of rims and will only be driven on track days.

And to come completely clean, even though I really like the MSport suspension on the '26 330i and I suspect it would be a fun challenging speed-maintenance car on track, I'm still playing with the car I already had. It's a 2015 Cayman GTS. I want to move to 18" rims and bump the tire width a bit. It would be 245/40-18 in front and 275/40-18 in back. 8" front rim. 9" rear. Other than the rim widths I think the combination would work pretty well.

And yes, thanks for the reply.

Well, sorry I don't think I can help too much with your scenario, though I am technically knowledgeable about bmw 3 series/m.

245/275 is a common stagger for E46 era bmw though to get equal circ, you drop down to a 35 profile on the rear 275.

But for your car in question, the 2026 330, I would find out what the stock sizings is and the stock stagger (are the square rims/tires or staggared?) and I wouldn't stray far from that (rolling circumference/profile) as you can cause nannies like traction control to freak out.

Generally speaking, stretched tires are faster than extra rubber. Wider tires just for the sake of being wider won't give you more grip and can even cause less grip. Obiously a wider rim can take a wider tire.

As for camber, maybe what you wrote was a typo, but you want NEGATIVE camber specs. SO the -1.5 you mentioned up front isn't too bad, but for tracking, to get even tire temps/contact, you may need more like -2.5 to -3 depending on your speed. Rear shouldn't be 2, maybe you meant -2.

I was kind of assuming the negative I guess. I hate to think how the car would drive with +2 in back. Essentially the front camber is at the limit of adjustment. The two track days so far with Michelin Pilot Sport 4S tires on 20" rims the car was well balanced under power exiting corners but had some intrinsic understeer off the power. Not surprising with the front McPherson strut suspension. More negative camber requires camber plates, which may happen some day.