crazyfrog

Hi,
Is it possible to fit 235/40/18 tyres and keep the 295/30/18 at the back ??
I have been offered a set of Toyo's R888 and front are 235.
Can it cause issues with diff/ PSM ?
Thanks.

PAULUNM

Diameter difference is too large. If you want that size up front, use a 315 30 18 in the rear.

crazyfrog

How much different it is in Diameter ? What is the tolereance front / back for the diff ?
Very hard to get a good choice of trackday tyres when sticking to stock size....

mcbit

On the Toyos you mention, the rears rotate 14 revs per mile faster than the fronts which is exactly the same as the stock Bridgestones...so you shouldn't have an issue.

"02996ttx50

are you saying that because you don't think he will have an issue, he won't?! back at ya kid

i had an 02 and an 03 and pirelli's asyms were stock oem fitment. are you sure you didn't have a bmw? lol

crazyfrog

I just checked , there is a difference of 10mm on the diameter between 225 and 235. Quite a fair bit ...
Any here been running 235 on the front ? Road and track ?

crazyfrog

10mm difference on Toyo R888.

stilov

10mm is the width difference. The second number is the aspect ratio and determines the height or diameter of the tire.

If the aspect ratio is 30 then you're looking 30% of the width difference in radius, multiply it by two for full diameter.

Clear as mud?

pete95zhn

235/40-18 & 295/30-18 is a standard set for a 996 GT3 mk2. ABS/PSM can handle a maximum of 5% differenece in tyres' circumference.

Those tyres have it like this:
Diameter: 645.2mm / 634.2mm
Circumference: 2027mm / 1992.4mm = 1,01%.

mcbit

Nope! Where I went to school, "shouldn't" and "won't" had different meanings.



Mine is a 2004 and came with PS2s and below are Tirerack's OEM listings for a 2004 turbo Coupe.

mcbit

Not quite that simple though, the rear tyres should rotate faster than the fronts which is why the viscous coupling always transmits some torque to the front axle. With the GT2 set up the fronts rotate faster than the rears.

When I bought my turbo, all 4 stock rims were bent to some degree and I was told that one of them would not be able to be straightened. I was looking at buying a single replacement rim when I found a set of very nice GT2 rims with unworn tyres on them for $3000 so I bought them and fitted to the car. Due to the bent original rims I had never really had much experience of driving the car at high speed. The new GT2 rims looked really good on the car filling out the wheel arches much better than the stock rim and tyre combo, however there were a few things which felt were not normal. On long sweeping bends at high speed the car would "nod"; on exiting bends with the power on, the carry would get very squirrelly on a subsequent direction change; the frunk would get quite warm; the front tyre would be running about 5C hotter than the rears.

In the meantime i had had managed to have all 4 stock rims successfully straightened so when I had a puncture on one of the GT2 rears I was able to put the stock rims and tires back on the while I imported some new tyres due to lack of availability locally. The differences I noticed were marked and immediate, gone was the nodding on sweepers which encouraged more speed and some gentle understeer, exiting the same corners with power on the car was much more solid on direction change and i could feel the drive transfer to the front as the rear would start to break away. The frunk now runs cool and the rears run a little hotter than the fronts. The biggest revelation though was the much improved acceleration at higher speeds, simply stunning.

Since I love the look of the GT2 rims, I was determined to get a set up which worked correctly on the car, so based on forum advice I bought some 245/40 R18s for the front which give the correct front/ rear wheel speed balance. These work fine most of the time but are binding somewhere on full lock reversing and will contact the arches at high speed on significant road dips.

Much as I love them, I have now given up trying to get the GT2 rims to work and am currently having the original rims painted and re-shod; believe me I am not doing this for the satisfaction of depleting my bank balance. It's a much better car to drive with the original rims.

"02996ttx50

well, that explains that. my 02 and 03 had pirelli's, but i marvel at your cut and paste abilities. i won't doubt them again, and shouldnt've lol cheers

mcbit

The nature of my employment requires me to present evidence when raising an argument; cut and paste is the easy bit.

"02996ttx50

ok, well for my part, i've never worked an honest day in my life so any argument i might have undertaken was purely for sport. but i see you like to play, and that to me, is all that matters

we shall meet again. so..until then

ps. sorry about your bridgestone oem fitment.

mcbit

I'll stop playing when I'm in my box...which, incidentally, is about the same time as I told my wife that I'd stop looking at other women.