Wider on Rims & Tires on a Z3 M Coupe. Changes in handling?

[calimanusa]

Hey guys, so I just bought a fully stock s52 coupe. I'm looking at getting some new rims and tires , going an 1" wider on both the front and rear. Was just wondering how it will affect the handling/performance? Any thoughts?

Rims - BBS CH 18x8.5 front, 18x10 rear
Tires Bridgetsone Potenza 225/40R18 front, 265/35R18 rear

Thanks in advance!

[Terry F.]

Another tire option is 245/35-18 front and 275/30-18 rear. You can certainly put more tire in there than your proposal.
Terry

[calimanusa]

Good to know, thanks!

[Scarceas]

You should have 225s up front stock. If you're going to add an inch of rim, why not add more rubber, too? 245s as Terry suggested would improve handling, and a 265 or 275 out back should keep something close to the factory balance but with overall improved grip. Unfortunately, these cars tend to understeer from the factory. I have been able to dial it out with air pressure (2-4 more psi up front than rear).

If you only add rubber in the back, it should make the car understeer even more. The rears on these cars can take huge rubber, though. If you throw 295s or something huge on the back and leave the fronts at 225 you will need to make some other adjustments to the car to get neutral handling. If you just like the look, go for it. I do think the huge tires in the back look great, personally, and even better with wide tires up front!

If I were in LA I might consider the BFG Rival tires.

[2000mkoop]

What's the offset of the wheels ?

[jonesmechanical]

If some is good, more is better. I wouldnt shy from going a bit wider in the rear, or the front for that matter. Its 100% all about offset and tire choice. You need to check the offsets. 35-40 offset in front. 0-20 offset on rear (spacers will be likely with higher range on a 10).

Another tire option is 245/35-18 front and 275/30-18 rear. You can certainly put more tire in there than your proposal.
Terry

Love the 245 35 size, never seen a 275 30. 285/295 30 will work nicely on 10's and keep the diameters in check. I have run 275 35 18's on a 10.5" wide 18 offset rear, and it didnt look right. It would have needed spacers, and it was a tall tire. Once i got a 295 30 on there i was pleased, 315's even more. Even on stock power, i never minded any stagger ive run. Its more about suspension setting than tires to ge the right balance. Stock suspension is annoying once you realize how nice it can be.

[varoom]

I have a question regarding increasing wheel/tire size as discussed in this thread. The OP mentioned getting new BBS wheels 18x8.5 and 18x10 (F/R). Assuming a stock suspension, how do you choose the width of the wheel? For example, TireRack shows 18x8 and 18x9 for replacement wheels.

How wide of an 18" tire can you put on 18x8 and 18x9 wheels with a stock suspension and do you stay the same as the OEM wheels: ET 41 & 8 (F/R)?

[rf900rkw]

The experts at Tire Rack highly recommend whatever they have to sell.

Greg's list in the post above yours gives the near maximum widths and offsets that will go under a stock M. 315s will go under the rear, but polish the dirt off of the inner panel. Use that as your outer envelope and calculate where your proposed setup stands. If you're bad at grade school math, there are many offset calculators online.

[gtwhimself]

Take this into account: my '99 M Roadster is fitted with 18in style 67 wheels. 8in et47 front, 9in et26 rear. Michelin all around. Fronts are 225x45, rears 255x40 - the front tires rub on tight turns and road bumps. Very bothersome.

[rf900rkw]

That's because you didn't stay inside the envelope. Your sucked in under the car with those offsets and the tires are a truckish inch too tall. Toss a 10mm spacer in the front, and a 20mm in the rear to get the tire centerlines back closer to stock and you will likely be fine.

[IndianaRoadster]

Here's my combination,
Rondell #0021 8x17 et 40 front
10x17 et 15 rear
Nitto 555 G2 Summer Ultra High Performance F 235-40-17 R 315-35-17
Screenshot_20230605_193201_Gallery.jpg
On the rear inside, I have about 10 mm of clearance from the side. I did have to slightly roll the fender lips, but with a et20 rear wheel, I would have been just fine.
Screenshot_20230605_193315_Gallery.jpg