Torsion bars on '87 Carrera track car
10-31-2003, 03:16 PM
#1
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Torsion bars on '87 Carrera track car
Hi, All,
I'm interested in your opinion (esp. F-Stockers) on torsion bars.
I need to increase the rear stiffness of my '87 Carrera track car. It works well at most tracks, but I have trouble with bottoming out the suspension and excessive front wheel lift at certain tracks. What I have now is:
'87 Carrera, 3000 lb with driver and full tank
Automotion tubular torsion bars, 28 mm rear, 22 mm front
Turbo tie rod ends
Strut brace
SRP custom valved Bilstein shocks (cut down bump stops according to SRP)
SRP polyurethane graphite bushings everywhere
TRG adjustable sway bars front and rear ("B" bar stiffness)
Adjustable front camber plates
Camber: -2 (front), -2.2 (rear)
Ride height (to tops of fenders): 24 3/4" front, 24 1/2" rear
Toe: +1/32" front, +1/8" rear
Corner balance: +/- 5 lbs cross weights
8&9x17" Fikse wheels w/Kumho Victoracer tires
I've been advised (Steve Weiner - hi, Steve!) to run 31 mm torsion bars in the rear and raise the car about 1/2-3/4". Sounds good, and I'm ready to do that. But before I do, what is the best torsion bar setup for F-Stock PCA Carreras? If I go to 31mm in the rear, will 22 in front still be OK? Should I go to even larger torsion bars in the rear (33mm)? If so, what about the fronts?
Thanks!
Will
I'm interested in your opinion (esp. F-Stockers) on torsion bars.
I need to increase the rear stiffness of my '87 Carrera track car. It works well at most tracks, but I have trouble with bottoming out the suspension and excessive front wheel lift at certain tracks. What I have now is:
'87 Carrera, 3000 lb with driver and full tank
Automotion tubular torsion bars, 28 mm rear, 22 mm front
Turbo tie rod ends
Strut brace
SRP custom valved Bilstein shocks (cut down bump stops according to SRP)
SRP polyurethane graphite bushings everywhere
TRG adjustable sway bars front and rear ("B" bar stiffness)
Adjustable front camber plates
Camber: -2 (front), -2.2 (rear)
Ride height (to tops of fenders): 24 3/4" front, 24 1/2" rear
Toe: +1/32" front, +1/8" rear
Corner balance: +/- 5 lbs cross weights
8&9x17" Fikse wheels w/Kumho Victoracer tires
I've been advised (Steve Weiner - hi, Steve!) to run 31 mm torsion bars in the rear and raise the car about 1/2-3/4". Sounds good, and I'm ready to do that. But before I do, what is the best torsion bar setup for F-Stock PCA Carreras? If I go to 31mm in the rear, will 22 in front still be OK? Should I go to even larger torsion bars in the rear (33mm)? If so, what about the fronts?
Thanks!
Will
10-31-2003, 04:05 PM
#2
Nordschleife Master
Will,
You are probably running 275/40/17 tires in the rear which have a rear diameter of 25.8" compared to stock size of 24.7" if you had the 245/45/16" wheel option. You'll be able to lower the car some before you start rubbing the QTR panel, but you'll definately need stiffer rear torsion bars. I had a ride height similar to yours, but had to raise it due to rubbing. Also, in the front, do you have the tie rod bump steer kit? You'll need something when you lower the car.
22s in the front with 28s in the rear proabaly causes your car to understeer quite a bit. They'll be better with the 31s. You certainly don't want to go stiffer in the front.
You are probably running 275/40/17 tires in the rear which have a rear diameter of 25.8" compared to stock size of 24.7" if you had the 245/45/16" wheel option. You'll be able to lower the car some before you start rubbing the QTR panel, but you'll definately need stiffer rear torsion bars. I had a ride height similar to yours, but had to raise it due to rubbing. Also, in the front, do you have the tie rod bump steer kit? You'll need something when you lower the car.
22s in the front with 28s in the rear proabaly causes your car to understeer quite a bit. They'll be better with the 31s. You certainly don't want to go stiffer in the front.
10-31-2003, 05:00 PM
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I have no trouble with understeer with the 22/28 combination, but my car is probably a few hundred pounds lighter and you have quite a few more suspension mods.
I don't believe that setting the ride height by height to the fender lip can be accurate given the different diameter of available tires. It seems that a more accurate measurement is the difference between the two measurements from the ground to center of the torsion bar and from the ground to the center of the axle. That measurement will not be affected by different tire sizes. I am not disputing anything that Steve says here, I am merely questioning the viability of the fender lip measurement. There is a half inch difference in ride height between the two tires mentioned in Geoffrey's post. For what its worth, I thought 23/31 would be a pretty good combination for your car. Also, you don't mention what size tires you have on your wheels. If you put 245/45s on a nine inch rim, it seems that diameter would be less then spec because the spec measured rim is 8 inches. Too many variables.
Please feel free to provide guidance if I am missing something here.
I don't believe that setting the ride height by height to the fender lip can be accurate given the different diameter of available tires. It seems that a more accurate measurement is the difference between the two measurements from the ground to center of the torsion bar and from the ground to the center of the axle. That measurement will not be affected by different tire sizes. I am not disputing anything that Steve says here, I am merely questioning the viability of the fender lip measurement. There is a half inch difference in ride height between the two tires mentioned in Geoffrey's post. For what its worth, I thought 23/31 would be a pretty good combination for your car. Also, you don't mention what size tires you have on your wheels. If you put 245/45s on a nine inch rim, it seems that diameter would be less then spec because the spec measured rim is 8 inches. Too many variables.
Please feel free to provide guidance if I am missing something here.
11-01-2003, 10:02 AM
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Thanks, guys. Regarding rear tire size, I'm running Kumho Victoracer 255/40-17's on 9x17" Fikses. At one point, I looked into the diameter of this setup and I believe it is very close to to stock Fuchs/tires.
I've tried the same size in Hoosiers, but they rub like crazy and I had to go down to 245/40's.
Anyway, it sounds like 22/31 torsion bars will be OK. I'm only hoping to avoid replacing the 28's in the rear with 31's only to find I now have to go back and stiffen up the fronts.
Will
I've tried the same size in Hoosiers, but they rub like crazy and I had to go down to 245/40's.
Anyway, it sounds like 22/31 torsion bars will be OK. I'm only hoping to avoid replacing the 28's in the rear with 31's only to find I now have to go back and stiffen up the fronts.
Will
11-01-2003, 02:52 PM
#5
RL Technical Advisor
Hi Will:
FWIW,......Cars like yours used in stock Club Racing classes use 23mm & 33mm T-bars. That's a good balance and with the proper shocks, do not ride harshly.
You have big sticky tires for that chassis and you need some decent spring rates to keep the bodywork off the tires and control the dynamics.
Just one more thing to think about,....
FWIW,......Cars like yours used in stock Club Racing classes use 23mm & 33mm T-bars. That's a good balance and with the proper shocks, do not ride harshly.
You have big sticky tires for that chassis and you need some decent spring rates to keep the bodywork off the tires and control the dynamics.
Just one more thing to think about,....
01-09-2004, 05:23 PM
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bump steer
[QUOTE]Originally posted by Steve Weiner-Rennsport Systems
[B]Hi Will:
FWIW,......Cars like yours used in stock Club Racing classes use 23mm & 33mm T-bars. That's a good balance and with the proper shocks, do not ride harshly.
Steve,
do you happen to know if a turbo tie rod bump steer kit is legal on the 911 for pca stock Class F?
[B]Hi Will:
FWIW,......Cars like yours used in stock Club Racing classes use 23mm & 33mm T-bars. That's a good balance and with the proper shocks, do not ride harshly.
Steve,
do you happen to know if a turbo tie rod bump steer kit is legal on the 911 for pca stock Class F?
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01-12-2004, 02:59 PM
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Thanks guys -
I'm going to stick to my fuchs for now, as they are very light and strong. When I can afford some custom 17's, perhaps I'll get some for better tire choices. Thanks again!
Chris
I'm going to stick to my fuchs for now, as they are very light and strong. When I can afford some custom 17's, perhaps I'll get some for better tire choices. Thanks again!
Chris
01-18-2004, 02:27 PM
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Pertaining to torsion bars, would 23mm and 33mm T-bars be really harsh with bilstein sports? I've heard different things from different people, and wanted to know your thoughts here on rennlist...
thanks - chris
thanks - chris
01-18-2004, 04:15 PM
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Chris,
After starting this thread at the end of October, my car is finally in the shop getting the torsion bars changed out (as well as a few other things!). Steve W., my mechanic (Tim Pott at Eurotec in Ann Arbor, MI) and I pow-wowed quite a few times over this and I decided that the right setup would be 23 mm (F) and 33 mm (R) t-bars. I ordered the Glen Sander bars from Steve, and they're works of art (not that anyone will see them). Tim Pott is a Porsche racer and knows how hard I drive the car, and the thinking was to get it done right the first time. "Go stiff" as he put it. When the track season gets rolling (mid April here in Michigan), I'll post an update.
Will
After starting this thread at the end of October, my car is finally in the shop getting the torsion bars changed out (as well as a few other things!). Steve W., my mechanic (Tim Pott at Eurotec in Ann Arbor, MI) and I pow-wowed quite a few times over this and I decided that the right setup would be 23 mm (F) and 33 mm (R) t-bars. I ordered the Glen Sander bars from Steve, and they're works of art (not that anyone will see them). Tim Pott is a Porsche racer and knows how hard I drive the car, and the thinking was to get it done right the first time. "Go stiff" as he put it. When the track season gets rolling (mid April here in Michigan), I'll post an update.
Will
01-19-2004, 07:45 AM
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Chris,
My car is a track-only car, primarily because it's already too stiff to enjoy on the bumpy roads of Michigan. Changing to 23/33 t-bars will undoubtedly make it even less pleasant to drive on the street. If I lived somewhere with good roads (Tampa?), the story would probably be quite different!
Will
My car is a track-only car, primarily because it's already too stiff to enjoy on the bumpy roads of Michigan. Changing to 23/33 t-bars will undoubtedly make it even less pleasant to drive on the street. If I lived somewhere with good roads (Tampa?), the story would probably be quite different!
Will
