GT2 Front Suspension
10-03-2009, 06:16 PM
#16
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10-03-2009, 09:05 PM
#18
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What bump steer always is...the steering wheel jumps violently in your hand under hard cornering when the suspension is forced to compress. It also happens going straight if you go though a large dip in the road with only one of the front wheels. MacPherson strut suspensions are notoriously bad for this problem when lowered beyond their designed operating parameters.
Better said by someone else
"Bump steer" is the toe-in change that the front or rear tire takes as it travels up or down. With poor bump-steer characteristics, a car will dart from side to side over bumpy roads and have potentially dangerous transient reactions.
Not long ago I drove a 993 RUF Turbo R (approx RS ride height) on our bumpy local track and the bump steer was so bad that it almost hurt my wrists
Better said by someone else
"Bump steer" is the toe-in change that the front or rear tire takes as it travels up or down. With poor bump-steer characteristics, a car will dart from side to side over bumpy roads and have potentially dangerous transient reactions.
Not long ago I drove a 993 RUF Turbo R (approx RS ride height) on our bumpy local track and the bump steer was so bad that it almost hurt my wrists
Last edited by Tuner1; 10-03-2009 at 09:07 PM. Reason: 1
10-03-2009, 09:30 PM
#19
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Sounds like "kick back" to me. Bump steer you don't feel in the steering wheel, but the car steers on its own as it goes over bumps. The fact that bump steer cannot be felt in the steering wheel very well is what makes it so dangerous. Kick back on the other hand is either annoying or not, depending on what you like.
I don't know if the uprights fix kick back.
I don't know if the uprights fix kick back.
10-03-2009, 10:00 PM
#20
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Bump steer can be felt in the steering wheel because the steering wheel needs constant corrections to keep the car on line through bumpy corners.
Last edited by Tuner1; 10-03-2009 at 10:09 PM. Reason: add
10-03-2009, 11:34 PM
#21
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My point is that kickback is commonly caused by wider wheels and/or smaller offset wheels and/or using spacers which gives the wheels a higher leverage than stock, thus transmitting bumps to the steering wheel more than stock.
Just trying to save you money on GT2 uprights if they might not fix your kickback...
On my car, I recently switched to wider wheels, 9", up front and converted to monoball suspension, and increased camber from -1.6 to -2.2, and the the kickback is much more noticable than before; ride height was not changed. GT2 uprights would likely not have any effect.
Just trying to save you money on GT2 uprights if they might not fix your kickback...
On my car, I recently switched to wider wheels, 9", up front and converted to monoball suspension, and increased camber from -1.6 to -2.2, and the the kickback is much more noticable than before; ride height was not changed. GT2 uprights would likely not have any effect.
Last edited by pstoppani; 10-03-2009 at 11:38 PM. Reason: add
10-04-2009, 12:33 AM
#22
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What offset are you using on your 9" front wheels and what size tires?
Mine are 18x9" +54.
Surprisingly Porsche fitted the 993 GT2 street cars with 18x9" front wheels that had quite a low offset (around +30mm IIRC) with no other front suspension geometry changes that I am aware of. This should result in a fair amount of kick back vs a stock 993TT but sadly I have never driven a real GT2 to find out!
Last edited by Tuner1; 10-04-2009 at 12:55 AM. Reason: GT2
10-04-2009, 04:48 PM
#25
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I can see these specifications adding to the steering wheel kick back but your #s are still far better than a stock GT2.
Did you have to do any fender lip rolling to fit these front wheels and tires with your -2.2 camber? How stiff are your spring rates?
Did you have to do any fender lip rolling to fit these front wheels and tires with your -2.2 camber? How stiff are your spring rates?
10-04-2009, 07:05 PM
#26
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Yes, fender rolling was required. I'm running PSS9 suspension so whatever that comes with in terms of spring stiffness.
10-05-2009, 11:47 PM
#27
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Just had Jeff Gamroth of Rothsport install GT2 uprights and other front suspension components, which with PSS10s (set at 4 front and 5 rear), is so amazing. I debated doing it because it wasn't free, wasn't sure I needed it, thought it might look like a "mod" rather than an "upgrade" at time of resale, etc. However, I love it. The car now has so much better turn-in, and it feels a lot more stable at all speeds and on all types of surfaces. Huge smile and many thanks to the Rothsport folks.
I definitely have bump steer at RS ride height, so I'm looking forward to fixing that.
I'm still not 100% decided on dampers. I am leaning heavily toward Moton Clubsport (thanks to advice from Steve W at Rennsport Systems) but I've heard recommendations for JRZ and KW from more than a couple of people. My car (2WD, 480-ish HP) is used 75% for track and occasional fun weekend drives, but I drive to the track. Right now I'm running the Ruf-valved PSS9s, but I find the setup far too soft at the track.
Thoughts from others running similar setups?
10-06-2009, 02:21 AM
#28
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Very odd, I'm at RS height and not only do I not get bumpsteer, the suspension tuner checked for bumpsteer and there isn't any... I'm on PSS9s (yeah, a little soft for a mostly track car but a good compromise for the street). All three of the kits you mentioned (Moton, JRZ and KW) are excellent and would recommend the one that you can get someone to setup properly.
10-06-2009, 09:55 AM
#29
Three Wheelin'
