996 Four Wheel Drive vs 997
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996 Four Wheel Drive vs 997
I have a 996 C4S and want to put Turbo Wheels from a 997 on it. I was told I had to change tire size because the 997 uses different diameter tires front to back where mine uses same diameter tires all around. How does the 997 get away with this? I assumed the transfer case was one to one ratio. Thanks
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Re: 996 Four Wheel Drive vs 997
There could be a split between the front and rear to allow for different sizes .. I think they have a Viscous differential between the front and rear that allows for a torque split
1993 RS America
Grand Prix White
Car #6
1974 911 Carrera (resides in Australia)
Light Yellow
1974 914-6 GT (resides in San Luis obispo)
1987 944 turbo (location unknown)
1979 911SC(Hummers have it)
1972 911T (location unknown)
Grand Prix White
Car #6
1974 911 Carrera (resides in Australia)
Light Yellow
1974 914-6 GT (resides in San Luis obispo)
1987 944 turbo (location unknown)
1979 911SC(Hummers have it)
1972 911T (location unknown)
- PAUL LARSON
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Re: 996 Four Wheel Drive vs 997
My 997 C2s has 235/19/35 on the fronts and 305/19/30
on the rears. I am pretty sure the C4s use these same tires.
Paul
on the rears. I am pretty sure the C4s use these same tires.
Paul
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Re: 996 Four Wheel Drive vs 997
Thanks Larry and Paul. Paul, your tires are almost 3/4 inch different diameters front to back. I have been told my car needs identical diameter tires, front and back. Larry is probably right, there is a split between front and rear on the newer cars that my car does not have.
Thanks again.
Thanks again.
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Re: 996 Four Wheel Drive vs 997
General concensus for 996 C4 C4s is to have no more than a 4% variation on the overall diameter.
Peter Lim
996 C4. AX6
996 C4. AX6
Re: 996 Four Wheel Drive vs 997
The 997 Turbo's front differential is computer controlled, and is programmed to look for the wheel rotation speeds that are consistent with it's tire diameters. Since the 996 front differential is a passive viscous coupling, any difference in wheel diameters can cause partial lockup of the differential when less than normal wheel slip is occuring. For example, a front tire that is slightly larger than the rear causes the viscous coupling to lock up prematurely. Somewhere on the PCA national tech forum is a post that indicates lockup occurs at about a 7% difference in axel rotation. Keeping front/rear diameter differences as small as possible maintains the stock behaviour of the rear to front torque transfer.
laserman21 wrote:I have a 996 C4S and want to put Turbo Wheels from a 997 on it. I was told I had to change tire size because the 997 uses different diameter tires front to back where mine uses same diameter tires all around. How does the 997 get away with this? I assumed the transfer case was one to one ratio. Thanks
Last edited by itacud on Mon Dec 01, 2008 4:48 pm, edited 1 time in total.
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Re: 996 Four Wheel Drive vs 997
Thank you, that is the answer I was looking for.
- PAUL LARSON
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Re: 996 Four Wheel Drive vs 997
The difference is 2 3/4". The fronts are 235 (9 1/4") and thelaserman21 wrote:Thanks Larry and Paul. Paul, your tires are almost 3/4 inch different diameters front to back. I have been told my car needs identical diameter tires, front and back. Larry is probably right, there is a split between front and rear on the newer cars that my car does not have.
Thanks again.
rears are 305 (12").
Paul
- Doug Clark
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Re: 996 Four Wheel Drive vs 997
You should listen to Paul - he is very fast (more than he should be)
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Re: 996 Four Wheel Drive vs 997
Paul it isnt the width that needs to be the same or within a certain size ,it is the diameter of the tires
1993 RS America
Grand Prix White
Car #6
1974 911 Carrera (resides in Australia)
Light Yellow
1974 914-6 GT (resides in San Luis obispo)
1987 944 turbo (location unknown)
1979 911SC(Hummers have it)
1972 911T (location unknown)
Grand Prix White
Car #6
1974 911 Carrera (resides in Australia)
Light Yellow
1974 914-6 GT (resides in San Luis obispo)
1987 944 turbo (location unknown)
1979 911SC(Hummers have it)
1972 911T (location unknown)
- Dan Thompson
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- Location: Auburn, CA
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