Need help to cure evil handling 997RS
09-17-2007, 11:20 AM
#46
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But seriously, when setting the car up with a proper crew, it is much easier to have them close to the suspension.
R+C
09-20-2007, 08:02 PM
#47
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Here is an update. Did an open track day yesterday. Car alignment checked and confirmed spot on. Front neg 2.5 deg with 2 mins of toe in per wheel. Caster 8 degrees. Rear neg 2.4 degrees (wider wheels in back) with 18 mins toe i per wheel. Sways in mid position front and rear. Wing set at 1/2 max angle of attack. Hoosier R6 18 inches.
The car handled very well. Note these were the same settings which gave me grief wih the 18 inch MPSC. Go figure. I did a session with Jean Francois Dumoulin (2 x 24 Hour Daytona winner driving a Porsche). He felt the car was nicely set up and well balanced.
I am now convinced that the cups were defective. They were sent to Michelinfor examination.
To whomever suggested hair spray as a lube for mounting Hoosiers, THANK YOU. The tires did not rotate on the rims!
Tire temps were within 6 degrees F across the tread in back and 5 degrees in front at LCMT.
Best,
The car handled very well. Note these were the same settings which gave me grief wih the 18 inch MPSC. Go figure. I did a session with Jean Francois Dumoulin (2 x 24 Hour Daytona winner driving a Porsche). He felt the car was nicely set up and well balanced.
I am now convinced that the cups were defective. They were sent to Michelinfor examination.
To whomever suggested hair spray as a lube for mounting Hoosiers, THANK YOU. The tires did not rotate on the rims!
Tire temps were within 6 degrees F across the tread in back and 5 degrees in front at LCMT.
Best,
09-20-2007, 09:56 PM
#48
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Bob, what were the tire diameters of the 18" cups vs R6's? I run 245/35/18 R6's and 305/30/18 VRL's which maintain the exact tire height ratio as stock. As someone else stated I think the 997's are extremely sensitive to variances in ratios.
09-21-2007, 12:32 AM
#49
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eclou - the tires were like yours. 245/305 18.
09-21-2007, 12:53 AM
#51
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I run 245/35/18 front. The 18" cups you listed at 235/40/18 and 315/30/18 have almost the same diameter, possibly causing:
1)confusion for the traction control algorithms and the braking bias since they are expecting a certain ratios of tire rotation - the 18" cups are giving less than expected wheel speed in the rear vs front, which would indicate rear "lockup" on braking and "less spin" when the rear is spinning on accel.
2)loss of rake is taking away downforce on your rear wing, lessening the amount of downforce which is maintained when on the 19" cups and 18" R6's. Try adjusting the wing rake to max with the 18" cups
1)confusion for the traction control algorithms and the braking bias since they are expecting a certain ratios of tire rotation - the 18" cups are giving less than expected wheel speed in the rear vs front, which would indicate rear "lockup" on braking and "less spin" when the rear is spinning on accel.
2)loss of rake is taking away downforce on your rear wing, lessening the amount of downforce which is maintained when on the 19" cups and 18" R6's. Try adjusting the wing rake to max with the 18" cups
