[dradernh]

Originally Posted by AmuroRay

Final wheel and tire specs, and how much clearance do you have?

Sorry to be slow replying; for some reason, I just saw your post.

Front: M Performance Brake Kit / Michelin Pilot Sport 4S 255/35-18 / Apex ARC-8 18X9 ET42 / VAC Motorsports 8mm Spacer / -2.6° Camber / (slightly) Pulled Fenders

Rear: M Performance Brake Kit / Michelin Pilot Sport 4S 255/35-18 / Apex ARC-8 18X9½ ET58 / Turner Motorsport 5mm Spacer / -2.2° Camber / (slightly) Pulled Fenders

The clearances are unmeasured. I did rub the front fender liners slightly, but that was only after I began running the car hard on the track at Mid-Ohio. I think it would be very unusual to lean that hard on a car on the street, so I don't expect any more rubbing (I'm done with the track). There’s been no rubbing on the insides, nor on the rear fender liners.

Originally Posted by Mr. F22

so in summary, both a 255/35 R888R with an offset of +42, as well as a 255/35 PS4s with an effective offset of +34 are working up front for your specific application, correct? The latter potentially also would work without the 8mm spacer if you were running the stock m-sport brakes in front? I see you are also running 2.6 camber, are you running camber plates to achieve this? I'm really trying to make 9" fronts work on the set I plan on buying for next season so appreciate the insight!

For anyone just tuning-in and to be completely accurate: the front R888R was a 255/40-17 (with the same section width of 10.2” as the 255/35-18 R888R). The 17X9 wheel offset was +42.

The shop concluded the reason the PS4S 255/35-18 mounted on an 18X9 ET42 ARC-8 in front didn’t come close to fitting was that the other change I made – installing the BMW M Performance Brake Kit – introduced something that caused a tire that should have fit to not fit. Note that the section width of the PS4S is the same 10.2” as the R888R, so that didn’t change. That seemed to me to make sense.

The shop suggested that the rotor hat height differed and that was the cause of the inside rubbing issue. We didn’t measure the two to know for sure. However, I just now went to Brembo’s site to look up the specs for both rotor assemblies, and Brembo shows the MPBK at 73.1mm in height and the M-Sport at 73.2mm. So, we still don’t know what caused the need for an 8mm front spacer to fit a mounted tire that we think should have fit.

As I’ve pointed out in many posts before, I’m not at all expert in these matters, and that’s why I use qualified shops to help me choose upgrades for my cars. I’ve no doubt that if I gave the car and the front M-Sport brakes back to the shop and asked them to figure out why the MPBK required an 8mm spacer, they’d figure it out fairly quickly after removing the front MPBK components.

Anyway, on to your questions:

1) Yes, an R888R with an effective 255/35-18 on an 18X9 ET42 and a PS4S 255/35-18 on an 18X9 ET42 with an 8mm spacer for an effective offset of +34 both fit in front

2) Yes, it’s my distinct impression that an 8mm spacer wouldn’t be required with the M-Sport brakes

3) Yes, I’m running camber plates that came with the TC Kline Racing coilover kit I bought and had TCK install for me. TCK also pulled my front fenders slightly (not enough to be visible as far as I’ve ever been able to tell).

Some other things:

One of the vendors here (HP Autosport, I think) mentioned that some coilover kits leave more inside room for a wider wheel/tire combo than do other kits. TCK’s coilover kit was one they listed as leaving more room. TCK’s kit is Koni-based (valved to TCK’s specs), so maybe that has something to do with it(?). That bit of information is an example of why I generally go to qualified shops to help me (keep from making more mistakes than I already do! ).

Again, I’m no expert, but I think you should plan on choosing components that leave you the most space possible to fit the wider front tires you want to run. Whether that’s narrower coilovers (if you end up getting them), camber plates that give you a minimum of -2.5° (my estimate), pulled fenders, or, and this obviously will generally make life easier, going with 245s in front instead of 255s, assuming you’re not aiming for square wheels and tires.

TCK’s recommendation to me for tires was 265 in the rear and 245 in front. When I asked him about understeer, he just waved it off as not being enough to be an issue. The context was driving on the track, as that was why I had him modify the car. With his experience, I didn’t doubt that his assessment was accurate. I was stuck on square tire widths, though, so I didn’t take his advice.

I go to experts with decades of racing and high-performance BMW street car performance-build experience for their advice, service, and products, but I don’t always follow the advice. I’ll be the first to admit that hasn’t always worked out.

If I could get the money back from all my purchases of wheels and tires over the years that turned out not to fit or that I never got around to using for one reason or another, I’d be able to take a nice vacation. The cheapest way to test the limits is to either find someone who knows the limits of what will fit with your setup, or, for many of us, to buy a single wheel and a single tire and do a test fit. When it turns out to fit, the latter is somewhat more expensive than buying pairs (or quads, when the setup is square), but it's cheaper when it turns out the combo doesn’t fit.

Good luck with it – please let us know what you end up running.