PorscheAddict

I've never seen this particular question addressed, so here goes: can the stock suspension 981's handle 245/35/20 and 285/35/20 RE71's on sport classic 20's? I'd prefer 18's or 19's, but don't have those yet. 245/35 should certainly work, but 285/35 is pretty big compared to the stock rear.

PCarOMFS

The first thing I'd be concerned about is making sure the tire diameters are as close to stock as possible. I believe a tolerance of +/- 3% of stock diameter is acceptable. Second, do you have wheels that are wide enough to accommodate the 285 rear tire? Third, assuming the diameter of tires is within or close to stock spec, you would want to make sure there is no rubbing on the fender well and strut. Chances are without an aggressive track alignment or wider wheels that do not require a spacer, you will be fine. In terms of grip of the tires, RE-71R tires are roughly equivalent in grip to MPSC2. I ran those on my CGTS with stock alignment and had no trouble with suspension components handling the extra grip. They are still a street tire albeit much better grip than stock tires. The only concern you may run into with this setup is a tendency to understeer with the extra grip in the rear. FWIW, I have a GT4 which runs 245/35/20 front and 295/30/20 rear. With stock alignment and medium/medium sway bar settings, it understeers a lot.

PorscheAddict

Thanks. Diameter is within tolerance by a little bit, 27.3" versus 27.9." 9.5" rear will work, barely. The question is just clearance. At -2.6 camber or so in front, I have a bit more room than stock. It also does not come close to understeering with that much camber. Only -1.8 out back, which feels good for now.

PCarOMFS

Did you use shims at the lower control arms or camber plates in the front? Or both? At -2.6 degrees of camber, caster might be an issue with a larger diameter tire creating some rubbing on the front of the fender lining. Caster is usually corrected with camber plates but adjustable thrust arm bushings may be needed if you used shims. I don't know what to tell you definitively other than try a test fitting.

PorscheAddict

LCA's. Caster is set at 9.5 on purpose with solid thrust pucks from RSS. Hoping someone has tried this combo before, because I can't get my hands on 285/20's without buying them (guess I could borrow some at a track day just in the parking lot).

storii

I am subscribing to this thread because am also thinking to go a similar direction as the OP's. I recently bought a used set of the OEM 20" Turbo wheels which are 1/2" wider in both front and rear than the original wheels. The new (to me) wheels came with the original stock tires (235F/265R) which look to be a bit too narrow for these wheels. I am thinking about going with MPS4S in 245/35/20 front and 275/35/20 rear. This combo will add 0.3" (7.62mm) to the overall diameter and be well within the 3% tolerance (more like 0.1%) discussed above. I believe these will add 3.81mm to the overall height while reducing the gap between the fender lip and the tire by 3.81mm and I'm fine with that.

My only concern is whether running tires in different sizes than OEM will jeopardize the warranty. The car is still under the original warranty and 2 more years of CPO protection will kick in after that. I conducted a brief search but could not find anything on the issue.

PorscheAddict

^ I wouldn't worry about a warranty issue. The modification has to at least arguably relate to the warrantied part, which would make it a stretch for them to deny anything for slightly wider tires (other than a fender liner or something that was messed up because of the change, of course).

PCarOMFS

Snowhound88

Any updates on this post, I to0 am thinking of trying to fit 285/35/20 on rear with the RE-71s?

ghartke

My 2014 MT CS w/PASM (bought in 2016 w/6800 miles on the clock) was a CPO car that came with 20" Sport Technos and Pirelli Pzeros in sizes 255/35-20 and 285/35-20. When I changed to RE-71Rs for AX, I discovered that Bridgestone doesn't make those tires in a 255 width, so I went with 245/35-20's on the front. I'll be putting on my third set this spring for the start of the new season (12 to 16 events and 7000-8000 miles per year). These tire sizes have never given me any trouble.

Regards,

Greg

PorscheAddict

I ended up just going 275/35/18 and 255/35/18 on Apex 18's with lots of camber.

Scooby921

I didn't know Bridgestone was making 20" RE-71R's. That's a really short, really stiff sidewall. Whomever mounts them may struggle a bit and risk scratching the wheels.

I've not seen anyone post about using a 285 in a 20" wheel, but there are a few people in the Autocross sub-forum who are running 285's on an 18" or 19" wheel and don't appear to have any issues. I was planning to go 285 in the rear on my car and opted to go for 265 just to compare the OEM Pirelli to an RE-71R in a nearly equal size (20" vs 19").

AZWCat

PorscheAddict

Can't remember off the top of my head, but the 18x9 18x10 option with most aggressive offsets. I'm at -2.75 camber or so, not sure how close to rubbing but pretty close.