Hello the forum, sorry if this has been covered already, I haven't found any threads that mention it.
While looking for winter wheel/tyre options I've noticed that the 235/40/18 + 295/35/18 are 645mm and 664mm diameter respectively. Differential of 19mm, around 3%.
Summer set up of 235/35/19 + 305/30/19 are 647 & 666mm same 19mm differential. For a given road speed both of the above set ups mean the front wheels rotate about 3% faster than rears.
Closer matching of tyre diameter can be achieved by going to a different profile and/or width.
e.g. Winter 235/45/18 + 295/35/18 which are 669 & 664 mm in diameter. Front wheels will rotate marginally slower than rears Or 235/45/18+305/35/18 @ 669 & 671 mm which would be back to front wheels faster.
These differentials should be of little or no consequence in a 2wd car apart from abs sensors seeing different wheel speeds front v rear.
Does anyone know how or if the 4wd control system for the 997.2 compensates for these differentials?
I've been Dyno testing recently and the traction control has been activating to reduce engine power at high speeds/loads and I'm wondering if the different diameters are a contributory factor. This is actually why I ended up with my head spinning faster than the wheels trying to figure out what's happening!
Anyway getting eventualy to the main point has anyone run the different profiles 45 front 35 rear profiles on the 4WD cars?
thanks for your patience
awrabest
Gordon.
While looking for winter wheel/tyre options I've noticed that the 235/40/18 + 295/35/18 are 645mm and 664mm diameter respectively. Differential of 19mm, around 3%.
Summer set up of 235/35/19 + 305/30/19 are 647 & 666mm same 19mm differential. For a given road speed both of the above set ups mean the front wheels rotate about 3% faster than rears.
Closer matching of tyre diameter can be achieved by going to a different profile and/or width.
e.g. Winter 235/45/18 + 295/35/18 which are 669 & 664 mm in diameter. Front wheels will rotate marginally slower than rears Or 235/45/18+305/35/18 @ 669 & 671 mm which would be back to front wheels faster.
These differentials should be of little or no consequence in a 2wd car apart from abs sensors seeing different wheel speeds front v rear.
Does anyone know how or if the 4wd control system for the 997.2 compensates for these differentials?
I've been Dyno testing recently and the traction control has been activating to reduce engine power at high speeds/loads and I'm wondering if the different diameters are a contributory factor. This is actually why I ended up with my head spinning faster than the wheels trying to figure out what's happening!
Anyway getting eventualy to the main point has anyone run the different profiles 45 front 35 rear profiles on the 4WD cars?
thanks for your patience
awrabest
Gordon.
