bbossier

Ok here’s the deal. My car is 2002 Porsche Carrera 4 Cabriolet. Original tire specs are front 225/40-18 and rear 285/30-18. The tires I want are the Michelin Pilot Super Sports. They comes in the right size for my front tire but the rear only comes in a 285/35-18. So the aspect ratio is 5% different which I calculate to be 9/16th of an inch. The Porsche people tell me not to do it for various technical reasons such as you don’t want to have an imbalance between the 2 axles (one spinning more or less than the other stresses the tranny etc).

So my question is if you were 5% off from stock on both then no problem?

Michelin does make a front 225/45-18. Would that work?

eagle11401

I wouldn't do it, I don't think that tire size on the rear is a good idea.

I delt with the same delima a month ago and after calling people far more knowledable than myself (several vendors and site sponsors) decided to avoid changing my rear tire size.

My understanding was you "may" be able to do a 265 but it wouldn't be worth it to put a narrower tire on the rear.

I ended up with some re11's on my c2 and so far so good. Worked well at roebling and decently quiet compared to the worn out ps2's I had.

roadsession

don't do it. you have AWD and PSM too which complicates matters. Stick with original circumference requirements from the manufacturer.

brad@tirerack.com

It's not a good idea to run the 35 series rear with the 225 front. The OD difference is too great. You really want to be within just a few percent change between the front and rear on an AWD car. 5% is too much on an AWD car. I have had people compensate some by switching to a 235/40 18 in the front. They are about .3" taller in OD from the 225 and help to take up some of the difference (2%).

235/40 and 285/35 is the closest that you will get if you must have Super Sports. If the car is lowered you may get some rubbing out of the back during hard acceleration.

bbossier

Great advice guys. It's clear I need to stay with the factory specs. Thanks.

DK570

I've been told you can run 265/35 18 in the rear, which is I believe is what the 996.1 cars use, 996.2 switched to 285/30 18.

Gaspasser19

You are correct. In fact, the 265/35 is actually a bit closer to the circumference of the 225/40 than the 285/30. They tend to be cheaper, too.

WalterRohrl

Resurrecting this thread, sorry. I have the exact same question as the OP except mine is a C2, not a C4.

My car has been experiencing a vibration that came and went, even after a rebalance, I am fairly sure it was caused by a set of spacers which are now off the car. However the front tires are still vibrating a bit and the tread blocks are squared off a bit.

Been strongly considering Micheling PS2 and Michelin PSS. PS2 is quite expensive and now kind of old compared to PSS, so looking at the PSS like the OP. Of course the sizes aren't correct.

My stock sizes are
225/40-18
285/30/18 (No, not 265, it's a Mk2)

SO...
Since the wheels are 18, I guess the ideal thing is to get the sidewall height the same which would keep the circumference the same. There are lots of options:

Rears:
285/30 NOT available in PSS but sidewall would be 85.5
285/35 would be a sidewall of 99.75 and is available so I guess that's the benchmark.

Fronts:
225/40 stock is a sidewall of 90
235/40 is a sidewall of 94
245/40 is a sidewall of 98 which appears to be pretty much perfect paired with 285/35 rears
245/35 is also available with a sidewall of 85.75 which would be perfect with a 285/30 rear but that is NA.

So - Am I way overthinking it or is 285/35 and 245/40 the way to go? Yes, my sidewalls will be taller than stock, right? But will it look like my Subaru Outback? A little extra sidewall couldn't hurt with some of the roads I drive on here but I like to think I'm fairly sensitive to tire roll and acceleration which will be slower with a taller tire.

I could just get the PS2's in the correct size and N3 spec but the $468 price difference is significant but not insurmountable if I will regret it otherwise.

Suspension is currently stock, plans include ROW M030 in the near future.

What's the consensus on the tire choice? No, I'm not interested in other tires really, I tried the Sumi HTRZIII on my spare rims and was not impressed, will be selling a lightly used set if anyone likes them. My only other real option is just to get another set of front PZero's as they were fine and I think I was the cause of ruining them in the first place.

tokyopav

I have the Michelin PSS 285/35 and 245/40 combination. To me they look fine. Nothing like a Subaru Outback.

Gaspasser19

The PSS are available in 265/35-18 which was the stock rear on the MkI 18" option wheel so I'm not sure why you wouldn't consider them. There's no reason you can't run those with 225/40-18 fronts. As I said above, the circumference difference front to rear is closer than with the 285/30-18. I've had them on for over a year now with no problems.

Schnauzer

Pilot Super Spots seem like a nice improvement over PS2s including price. Ideally they will start making 295/30-18 for my 2003 C4S before I need them next spring. Until then, Damon's recommendation seems right to me. I have 235/40-18 and 285/35-18 Michelin A/S 3 all season tires on now for the winter. No clearance problems on the front. I have heard that 245/40-18s might rub a bit against the spring perch on the inside.

The front to rear diameter difference with 235/40-18 and 285/35-18 is 2% (larger in the rear). The 225/40-18 and 295/30-18 standard sizes are close to the same when new. Interestingly the difference with the 235 285 combination goes down as the rear tires wear and is zero if the rears are half worn out but the fronts are still almost new.

Some people are adamant that you run only the sizes Porsche recommends but I see plenty of people using other sizes that are close in diameter. There are a lot more choices now than there were in 2003.

Rubik

Mine are also due for a replacement. I'm thinking about PSS 235/40-18 & 285/35-18. Fortunately, I have a C2 so I don't need to worry about drivetrain only PSM. And aspect ratio is +2% rear. I'm told there's nothing to worry about.

WalterRohrl

My only reason for not going 265 is that I like the way my 285 PZero's fill out the rim. My 285 (yes, same size) Sumitomos look very stretched. I'm thinking the 265 of anything will look stretched and would rather have the extra rubber. (My 265 Blizzaks look stretched). There is probably a reason why Porsche gave the Mk2's an extra 20mm rubber on the same width wheel. That being said a 285 - 225 results is a fair amount of understeer. The 265 would probably reduce it and going to a 285 - 245 would I think make it more neutral with greater overall grip.

Thanks for everyone's comments though, I appreciate it.

bal

I would hope that this was checked during the rebalancing but in my case, my rear wheels were bent - one more so than the other. I elected to have the worst offender repaired (some kind of hydraulic method) and the vibration has gone.

Blk_flatsix

Sorry I can't provide any advice.

But since Michelin PSS are being mentioned I have a set Iam about to throw on the rear. Just wanted to shamlessly show off. I have never bought a set of brand new tires