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I recently put 18" BBS wheels and snow tires on my 997TT and shortly afterwards noticed stuttering/hesitation between 2000-4000 rpm when not under boost and at partial throttle. Under boost or more than 50% throttle the car is smooth as can be.
Assuming it was the MAF sensor, I removed and cleaned both, without seeing positive results. I then ran the tank empty and refilled with another brand of premium fuel, again, no change.
So I scheduled an appointment with my local service department who, though unable to test, believe that the AWD clutch is slipping due to the wheels being 18" vs the stock 19" diameter wheels. The dealer did not have a set of 997 stock wheels to test their theory, but were otherwise unable to identify any issues or fault with the vehicle.
Has anyone else experienced this? Before I pick the car back up and swap my summer tires back on and retire the vehicle to good weather, wanted to see the forum's take.
If my math is correct from the tire sizes posted there is almost no difference in rolling diameter compared to stock and no difference in the front to rear diameter ratio which would cause problems with the center differential. However the diameter is just slightly shorter for the winters which means the speedo would be also slightly off as would any thing triggered off of vehicle speed but the difference is so small I don't think it would affect anything noticeably.
In my simple spreadsheet the comparison set is highlighted in yellow ("STOCK 997tt" versus "Shorter").
Last edited by Dodaleca; 02-28-2019 at 12:07 AM.
Reason: Match titles in text with those in spreadsheet snapshot.
If my math is correct from the tire sizes posted there is almost no difference in rolling diameter compared to stock and no difference in the front to rear diameter ratio which would cause problems with the center differential. However the diameter is just slightly shorter for the winters which means the speedo would be also slightly off as would any thing triggered off of vehicle speed but the difference is so small I don't think it would affect anything noticeably.
In my simple spreadsheet the comparison set is highlighted in yellow ("STOCK 997tt" versus "Shorter").
Glad to know I'm not the only person who uses a spreadsheet whenever possible!
02-27-2019, 06:32 PM
18" winter wheels causing AWD slippage?
