ca993twin

eclou,

Yes, you just repeated what I said. Except that the stock sizes (225x40x18, 285x35x18) is not exactly a 0% difference, F:R diameter, but its pretty close.

BTW, The differential is not what is stressed... its the viscous coupler.

eclou

I got a front and rear diameter specs of (225/40/18) 25.2" and (285/30/18) 24.7" for a ratio of 1.016. The tires I am using now are (235) 25.5" and (305) 26.2" for a ratio of 0.973. There is about a 4% difference (1.016-0.973)/1.016. Changing to the 245/35/19 front size makes the front diameter 25.8" so 25.8/26.2= 0.984. (1.016-0.984)/1.106 = 3% difference. I don't know how much the viscous coupler (thanks for the correction) can tolerate before it becomes unhappy. Does anyone know?

LAT

Eugene; not certain about the viscous coupler but RS Tuning informed me about tire sizes as follows.

With my combination and the one that RS recommends for our cars. 235/40 x 18, fronts and 285/35 x 18, rears has 2% taller rears 25.9" vs 25.4".

It is the ABS which is affected but not until 330 KPH and not an issue with the AWD.

sfbanchs

so assuming we have upgraded to 19s what is the best tire size, thanks steve for the explanation btw

eclou

The combo I found closest to stock was 235/35/19 front and 315/25/19 rear. The 315's are a very tough size to find though. Levino if its just the ABS then I will feel more at ease. I searched here and on the 993 subforums for "diff failures" and found very little. I might try "viscous coupler" next per Steve's correction

LAT

My information is from Gerhard at RS Tuning by telephone.

If you recall my car came with 295/30 x 18 in the rear and the spec sheet from RS states the 285/35 x 18 mentioned. To avoid confusion and because of my concern regarding the diff as well I called.

If it ever stops snowing up here I will actually go get the car and bring it home. We got 8" of the white stuff on Friday.

sfbanchs

unfortunately i cannot find 315 25 19 pirellis i would have to change out all four

LAT

sfbachs; I had the same problem looking for 285/35 18 Michelins and so I swapped out all 4 to Yoko Advan Sports.

I have not driven the car yet but my research indicates I will be fine with my choice.

sfbanchs

i just put yoko s drives on my audi and they work great hmm

ca993twin

Sebastian,

Yoko makes the combo that fits perfectly: 255x30x19 and 315x25x19. Check your present tires to see if you have enuff rim width to use those 255s on the front... they are a PERFECT fit on my Ruf wheels.

sfbanchs

thanks steve only problem is that i just bought a new pair of p zeros for the rear and my fronts have a lot of life left aren't you running p zeros?

ca993twin

Sebastion, I err.... am sorta. I had 255x30x19 and 305x25x19 P zeros. My rears wore out, and Pirelli discontinued that size. I went to Continental and got the 315x25x19. These are NOT a great match for the fronts, as the sidewalls have a bit more flex than the Pirellis, and I have to run a higher pressure to get decent balance. Next time around, I may get the Yoks, and get all 4. But money was tight, and that was all I could do.

Bradford

Playing around with bumpers and exhaust

sfbanchs

nice one scott

Turbodan

Scott looks very cool