Tire rotation can also effect abs. Because our car has a threshold of front to rear revolution ratios that won't negatively create ABS issues.

 

i did not know that, thanks. but if our cars have a "negative threshold that won't create abs issues"(?)

then i'm not sure i follow your point and i've misunderstood. my point was simply that the adherence to the suggested tolerances the AWD system requires to operate as intended, demands that the rear tires rotate faster than the fronts and some degree of torque is always transmitted rear to front, hence Porsche claims of a nominal minimum split of 5%FR 95%RR. this from mcbits explanation from an old post says it better than i can: given that, "The torque transmitted to the front wheels will increase with speed as the differential speed across the viscous coupling also increase with speed. The nominal split assigned by Porsche may be questionable since OEM Bridgestones on a tt have have a rev per mile difference of 14 front to rear while with OEM Michelins the rev per mile difference is only 3 which means there should also be a difference in torque transmission. This also suggests that Porsche feel that a 3.8% (14/837) difference in the rev per mile rating rev rating is OK for the components of the awd system."

so it appears the necessity of staying within the vaunted 3%+/- front to rear has more to do with the front differential needing the rears be equal or taller than fronts so that undue and constant friction isn't always heating the viscous fluid to the front diff.. but again, if you're saying that the ratios also impact the abs system? ok, not knowing any differently? i'll go with that, thanks. but again, obviously if running rwd? then none of the foregoing actually applies. at least not as relates the front differential. but abs affected? again, didn't know that.

 

255/35 works too but you probably wouldn't track with that size and stock rim.

 

VAG is correct. The stock ABS system starts to freak out once you get in excess of 1" or larger differential in diameters. Becomes more susceptible to ice mode when pushed hard. Not really an issue for street use but becomes problematic on track especially bumpy ones. That's one of the reasons why I switched to the Cup ABS which has logic for higher thresholds and also programmed for a +1" larger rear tire. There is also no ice mode programmed into the motorsport ABS

 

I also run these exact size on the stock twists with no issues at all, primarily did not go to the 315/30 18 due to very limited choices in the tires, the conti DW's really work well for the car, very smooth and quiet. I'll try the Pilot super sports next go round tho, now that they are available in the same sizes


front 25.7" rear 26.0 btw


lol on a side note tire rack has the Conti DW on sale 295's for 183.00 each and a 70.00 rebate card on a set, fronts are 139.00 pretty good pricing