18 inch rims
08-28-2001, 12:01 PM
#2
Rennlist Member
Yes, it's possible, and some people have done it. However Porsche issued two service bulletins early on noting that 18" rims were not approved for 964s. I don't remember the
details of the reasons given (had to do with
vibration and wear as I recall), but that was
enough to keep me from considering 18" wheels.
details of the reasons given (had to do with
vibration and wear as I recall), but that was
enough to keep me from considering 18" wheels.
08-29-2001, 09:28 AM
#3
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Dear Jim,
You are 100% correct but the TSBs were for road use. I would hope that this Cup car is not running standard wheel suspension. If you install the Turbo wheel suspension system then the problem is basically solved.
The problem was stress induced cracking in the wheel carriers and various bolts being broken off by the extra forces generated by the 18 inch wheels.
According to some data I have seen these forces are doubled when comparing a 7JX17 front wheel with a 8JX18 assembly. Also the stickier the tyres used the greater the stress. A 225 slick creates over 100% more load on the stress bearing components as compared to a standard 205 high performance road tyre. I hope this data is published officially soon. Porsche also have this data but it is not available to the likes of me,
Ciao,
Adrian
911C4
You are 100% correct but the TSBs were for road use. I would hope that this Cup car is not running standard wheel suspension. If you install the Turbo wheel suspension system then the problem is basically solved.
The problem was stress induced cracking in the wheel carriers and various bolts being broken off by the extra forces generated by the 18 inch wheels.
According to some data I have seen these forces are doubled when comparing a 7JX17 front wheel with a 8JX18 assembly. Also the stickier the tyres used the greater the stress. A 225 slick creates over 100% more load on the stress bearing components as compared to a standard 205 high performance road tyre. I hope this data is published officially soon. Porsche also have this data but it is not available to the likes of me,
Ciao,
Adrian
911C4
09-01-2001, 12:41 PM
#4
Rennlist Member
Later Carrera Cup racing cars had 3 piece 18" wheels: 8" ET52 3.6 Turbo fronts and special 9.5" ET47 rears. I believe these cars also used the Turbo 3.6 front suspension upright (? reinforced) part number 964.341.655.21, but I am not sure of this.