Widest front tire/wheel for non-M z4

[dre99gsx]

I've seen folks run 275/35 up front for Z4M, so I know it can be done with minor modification.

For those of you who race non-M 3.0si or such, have you fitted at 275 up front and if so, what wheel offset worked for you?

I'm planning to go Apex wheel route but can't find any offset info for 275 fitment for the non-M.

For reference, I have run 265/35-18 on 18x9.0 et30 Apex wheels with no issue. I just can't fit a 275 on this rim.

EDIT: May have answered my own question. I tried to fit my rear 9.5 et35 in the front with 275/35, and it hits the shock tower of my KW Clubsport. I inserted a 5mm spacer I had laying around and it clears. So, looks like this wheel size would fit with a 5mm spacer. That then brings the question of what issues I'll have with fender liner at -3.8camber.

FYI - this is on a ARC-8 wheel with Direzza Star-spec II tires (fairly old) 275/35/18

[3002 tii]

Good stuff, what tire brand and model?

So basically 9.5 et30 with 3.8* to clear strut side. Can you take pics of how it sits on the fender currently? And remind me again, are KW CS front springs beehive style or narrow linear?

[dre99gsx]

I updated my original thread, but yes:

>So basically 9.5 et30 with 3.8* to clear strut side. Can you take pics of how it sits on the fender currently? And remind me again, are KW CS front springs beehive style or narrow linear?

I'll try to grab a photo but the tire sidewall rubs on the lower KW CS adjustable ring right beneath the seat of the spring. These are swift springs, narrow linear. They are slightly wider than the adjustable collar. 5mm out clears them both with about 1mm gap to spare.

I didn't lower the car on the ground to check clearance on the outer edge with the fender nor how much impact I'll have with the liner. I assume this would be similar to Z4M but the wheel does stick out more than my original 255s...

Because I run 295/30 in the rear, this will be much taller, so I'm not planning to run 275s until I can find a way to fit 315s in the rear. Otherwise, I have to continue running 255s and live with it.

[Michael9218]

Not sure the differences of the non-M, but on my M I fit 275’s with Arc-8 9.5” et35 with a 5mm spacer to clear both the caliper/spokes and the strut spring perch (MCS with short 5” springs that put the perch at the tire shoulder).

Scrub radius was also an issue. I had to shave 3/4” off the rear of the bumper cover and push the fender liner in.

Run square for better tire management.

[dre99gsx]

Wait.. so the fact I can also fit a 9.5 et35 on the non-M with 5mm spacer for clearance indicates the non-M/M have similar "back spacing" up there.

So the concern would be the front spacing. I have no way to properly measure how much past the fender I am vs. a M and if I may have worse issues with rubbing.

Good info though...

[dre99gsx]

I did some more measurements. With 5mm spacer, I have 1mm gap between tire rubber/lip and the shock perch.

The tire moved .5" inward from my current 255 tire setup, which leaves .2" left on the outside of the tire to make up the 0.7" wider section width of these 275s to 255s.

Not comfortable with 5mm spacers as there is barely any hub lip left for the rim to sit in as "hub centric". Don't know how you guys race with 5mm spacers...

[F360C]

Originally Posted by dre99gsx

I did some more measurements. With 5mm spacer, I have 1mm gap between tire rubber/lip and the shock perch.

The tire moved .5" inward from my current 255 tire setup, which leaves .2" left on the outside of the tire to make up the 0.7" wider section width of these 275s to 255s.

Not comfortable with 5mm spacers as there is barely any hub lip left for the rim to sit in as "hub centric". Don't know how you guys race with 5mm spacers...

You can get a hub extender from Turner Motorsport for $40 to safely run a 5mm spacer. They just replace the dust cap.

To run the 275 on the Z4M I had to run the 5mm spacer for strut clearance. That said I recently switched backed down to a 265 because i didnt want to run the spacer due to increased scrub radius. If you can get away without running the spacer do it!

[dre99gsx]

Thanks for the tip! I ordered them. Having said that, I agree with you. I'm looking at options to go wider but I have run 265 in the past as R888R. Toyo RR doesn't carry them.

[dre99gsx]

UPDATE: I finally got the RR 275/35 mounted on the 9.5" ET35 wheel and tested with the 5mm spacer.

I couldn't get a piece of paper between rubber and shock lower perch. So, I removed the spring and reassembled the shock and tried to find how high I can go before I hit the bump stop.

I measured 9 1/8" between the bottom of the fender arc and the top of one of the studs in the 12' oclock position. I put my older 255/35 wheel on and was surprised that the fender is about half way down the tire sidewall. I though these KWs had more travel before the bump stop...

Next, I put the 275/35 on with 5mm spacer, and I couldn't get the tire to tuck much under the fender. It just sticks out too much and hits the fender right after the tread limit symbol.

So, I had some older BC racing 120mm (4.75") springs in the same rate as my swift 6" springs, so I went and swapped them while moving the lower perch up about 37mm to compensate for same ride height.

I installed the 275/35 without 5mm spacer and it clears the perch with <1mm to spare. The thick purple bottom ring just needs some grinding on the very edge and it will be golden.

I'm able to now tuck the wheel in to about where I would hit the bumpstop and turn the steering ~100deg to the right and it clears the fender liner as well.

Looks like this will work.

My only concern is really two things:
- I guess going from my swift springs to the BC springs is a "downgrade" but I'm not sure I'll notice any real difference...
- going from 6" to 4.75" spring at 12kg, I suspect I'm going to lose suspension travel and compress the spring earlier, potentially causing problems. Swift has a 5" (127mm) spring but that will move my lower perch further down and require I run ~3mm spacer or so. I did the math and my KW has 4" of travel before hitting the bumpstop. The 4.75" spring binds after 2.75" travel, which means I'll most likely bottom out the spring on the track. The 6" spring has 3.88" travel, will also bind before the bump stop but I haven't seen signs of binding on the spring, so I'm probably still safe on that length. I don't think I want to risk the 4.75" spring.

Original Clubsports come with 80-170 (400lb spring at 170mm (6.7") length), with about 2.4" solid height, giving roughly 4.3" travel, which would allow the bump stop to get hit but just barely...

After doing the math, I may just remove the helper spring altogether. If I do this, I have 1" gap between the spring and the perch when the car is lifted in the air. Not sure I will see this situation on the track...

[2one3E90]

i rub with 255 40 17. Stock 2.5i suspension.

[3002 tii]

I’d like to know if 265/35 is possible on stock suspension with max camber (pins + shims) of ~2.5* up front on 18x9.5 et35. Tire in question is AD09 (very wide 200tw summer tire)