mklein9

Have searched and not found a direct answer to this.

The reason for asking the question is that I need to replace my rear tires soon and the best replacement are PS2s which will cost about $1k installed (current tires front and rear are Pilot Sports, 6 years old in front and 5 years old in rear).

Current sizes are 225/40-18, 285/30-18, diameter 25.1" (calculated). They are on Carrera lightweight 8" and 10" rims.

Pilot Super Sports, widely considered a superior tire, would cost just a little more for a full set, but aren't available in my rear size. The rears are available in a 35 aspect ratio, but that would increase diameter 0.8" (3.3%) over the fronts which is likely to cause PSM/ABS issues.

However, if I move up to a 45 aspect ratio in the fronts, the Super Sports are available in equal diameters of 25.9" front and rear.

Therefore the question: is a 25.9" diameter tire a problem? Tire widths are stock. I measure maybe 0.6 - 0.7" of room above the inside edge of the tire to the front strut flange, but do not know how or whether a taller tire might rub on the fender under hard cornering, or whether tire deformation under lateral forces might push it against the strut flange.

The car has the X74 suspension so is low to begin with. (Yes, these would add 0.4" to the ground clearance.)

morganabowen

I have 285x30x19 Bridgestone on the rear and I had tried to put 305s, but too wide. Since you have 18s, you might be able to do the 305s. Check with you local tire dealer or check with Eli over at Wheel Dynamics. The majority of his customers are Porsches He is very nice and very very knowledgeable

6ta1

Not sure if the link will work:
http://www.1010tires.com/Tools/Tire-...0R18/295-30R19

I am running 295/30/19 rears on my 40th anniversary with H&R springs - as low or lower than your picture.

This size is almost 26" and fits ok. I have a very slight rubbing issue at the front at full lock and rears will rub the fender at full compression but due to the width and not the diameter

hope this helps

fasteddie99

235f/285r on 8 and 10 inch rims.
No rubbing, but I'm at the max, given my suspension set up.

morganabowen

What size are your front tires on your 18" wheels

MiamiC70

2004 40th Anniversary 235/40/18 front 285/30/18 rear on Victor Innsbruck rims 8.5"x18 front 10.5" rear w/ 55mm offsets.
I had 295/30/18 on OEM 10x18 rims and they fit fine but with the x74 unless you roll fenders "may" be tight so I backed down to 285.

Jake Ok

235/40/18 front....rubs when you turn wheel all the way. Rear 295/30/18 no probs.

alpine003

It would depend on offset, camber, rolled fenders, if you're using coilovers, etc.

I'll be running 245 front and 295 rears on my NB starting next week.

996pp

Im also running 295/30/18 on rear and 235/40/18 on front with PSS9 coilovers. No rubbing issues

Ray S

I've run with 235/40/18 front and 295/30/18 rears with the x74 on my '02 with no issues. My wheels are GT3 size and offsets and that's the key IMHO.

mklein9

So far interesting data but it appears most people are more interested in wider tires. But this question is specifically about standard width but taller aspect ratio, i.e. maximum diameter given standard width. And maybe with a touch more emphasis on the fronts than the rears. The benefit is that you can get PSS's all around on stock 18" wheels and still match diameters front to rear.

6ta1's experience with 295/30-19 is the closest answer and given that they fit even though they are wider and a touch taller than what I'm considering is good news. 6ta1, what size are you running on the fronts?

Jake Ok

Sorry...forgot to mention I have 10mm spacers. oopps

Sneaky Pete

Mike.....personally I would not go for the taller tire. Taller sidewall means not as stiff. The sizes you are looking at are dimensionally fine. If you can go wider but not taller would be better. I have 35's on the rear which are taller than 30's but the wider contact patch that the 35's (295) gave me sealed my choice. If PSS came in a 295/30 that would be the ticket. I know I'm contradicting myself but what I have works well for me.

6ta1

my fronts are 235/35/19 which doesn't help you much (25.5" diameter according to 1010tires)

as I mentioned earlier the fronts rub at full lock but never in "driving" condition

mklein9

Yow, I ran into this posting on the Michelin forum dated 11/21/2012:

"We are currently working with Porsche on their latest models with the Michelin Pilot Super Sport and not on the Porsche 911 type 997 models. Therefore we will continue with our current technical approvals on the Porsche 911 type 997 models for the foreseeable future - that is the N specification Michelin Pilot Sport PS2's, and the N specification Michelin Pilot Sport Cup+ tyres for certain applications. We do not expect to have a Porsche approved Pilot Super Sport fitment for the 911 type 997 models until at least 2014."

http://motorsport.michelin.co.uk/forum/viewtopic.php?f=8&t=18#p307


So that probably makes it even less likely the 996 will be supported in the next couple of years.

So either you go with odd sizes, or use a different tire.