Alignment settings and understeer
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Racer
Joined: Jun 2001
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From: Danvers, Mass.
Alignment settings and understeer
With stock 17 inch tires and alignment settings the car had a pretty good feel. After adding the 18's and adding Neg. 1 degree camber in front and neg 2 degrees camber in back the car seems to be twichy at higher speeds. The inherent understeer really bothers me and I want to eliminate it if I can. Ive got 225 fronts and 285 rears and I have found that 40psi all around seems to be good to start with. Any comments/suggestions? Please help if you can.
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Totally opposite experience here. When I test drove a 996 with 17"s, I took it back in 5 minutes because the push was HORRIFIC. An 18" equipped 996 was night and day! This was exactly the experience I had with my 993 upon changing from 17"s to 18"s.
My 996 (18" 225/285) has 1 deg front and 1.5 rear together with coilovers and GT3 adjustable sway bars. It has basically no understeer tendancy, but I think this is a result of sway bar settings. If you are unwilling to upgrade the suspension to rid the car of push, many have put 245s on the front and obtained similar results.
My 996 (18" 225/285) has 1 deg front and 1.5 rear together with coilovers and GT3 adjustable sway bars. It has basically no understeer tendancy, but I think this is a result of sway bar settings. If you are unwilling to upgrade the suspension to rid the car of push, many have put 245s on the front and obtained similar results.
RL Technical Advisor
Joined: May 2001
Posts: 11,870
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From: Portland Oregon
Hi John:
If I were you, I'd surely drop your tire pressures down to 34/36 or 35/37 and try that. At 40 psi, those 225 front tires are NOT flat on the road and that will really aggravate the car's natural tendency to push. This will also aleviate the "nervousness" you are feeling.
One other thing, if they didn't set the F&R toe correctly, your car will be very twitchy,.......!
Like Ben said, the real solution lies in installing suspension components that permits you to set the car's understeer/oversteer balance to your tastes. Done properly, this will not have a negative impact on ride quality.
Let me know how this turns out.
If I were you, I'd surely drop your tire pressures down to 34/36 or 35/37 and try that. At 40 psi, those 225 front tires are NOT flat on the road and that will really aggravate the car's natural tendency to push. This will also aleviate the "nervousness" you are feeling.
One other thing, if they didn't set the F&R toe correctly, your car will be very twitchy,.......!
Like Ben said, the real solution lies in installing suspension components that permits you to set the car's understeer/oversteer balance to your tastes. Done properly, this will not have a negative impact on ride quality.
Let me know how this turns out.
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Great point (as usual) about the tire pressures - ESPECIALLY the front at 40. 40 is WAY too much for the front. The ride must be crap - especially over road imperfections and the car must "hunt" or "tramline" something fierce with 40 lbs in the front. Like Steve said, reducing the factory recommended 8 lb differential between the front and rear pressures should help reduce (while certainly not even coming close to removing it) understeer. While more pressure is probably needed in the back owing to the 40/60 weight distribution, it's the differencial in ft/rr pressures that encourages even more the understeer the suspension is set up for.
1st Gear
Joined: Apr 2002
Posts: 1
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From: Columbus,Ohio
I have found that with all high performance
vehicles that tire pressure is one of the most
important aspect of the vehicle's driving dynamics
also one of the least understood.
It is Imperative to follow specific PSI
recommendations. I have noticed that he PSM
system in my 2002 996 C2 will respond differently
with different BAR settings..Having Owned M3's
Corvettes et all..you will find that "exacting"
pressures are what the OEM vehicle and tire manufactures work together.. In fact, great article in Porsche Magazine last Month..
vehicles that tire pressure is one of the most
important aspect of the vehicle's driving dynamics
also one of the least understood.
It is Imperative to follow specific PSI
recommendations. I have noticed that he PSM
system in my 2002 996 C2 will respond differently
with different BAR settings..Having Owned M3's
Corvettes et all..you will find that "exacting"
pressures are what the OEM vehicle and tire manufactures work together.. In fact, great article in Porsche Magazine last Month..
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Joined: Oct 2001
Posts: 52
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From: Boston
John your killin me. Your car is twichy because you added more negative camber and your car is now riding on a lot less "tire patch". Combined with the relatively high pressure you have set the tires at and you are going to get a lot of that "feeling". The idea of negative camber is to increase the amount of tire that touches the ground under cornering. Other drawbacks will be a noticable amount of wear on the inside of the tires and the tenancy for the ABS/PSM to activate easier in a straight line situation. My car is running 2.8 degrees neg in front and 2.4 in the rear. With the streets on the car feels rock solid up into the 120's no problem but I have lots of suspension done to the car. Bridgestone S03s 245 and 285.
On the track, I am running 245's front and 285's Hoosiers, and I am still trying to get the back to bite, the car drifted under power at Lime Rock yesterday at 100mph!
On the track, I am running 245's front and 285's Hoosiers, and I am still trying to get the back to bite, the car drifted under power at Lime Rock yesterday at 100mph!
Thread Starter
Racer
Joined: Jun 2001
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From: Danvers, Mass.
Dennis,
I set the tire pressure at 36 fromt 40 rear. Its better than before. I think maybe Im not used to such a light front end. The turn-in is great, its just the understeer while under throttle in the turns.
At 145mph the car was wandering and I had to almost fight it to keep it in line. My last Porsche was ROCK SOILD at this speed and anything under it as well.
Maybe Im just a 928 type of guy....
Former owner of:
1983 928S
1991 928GT
I set the tire pressure at 36 fromt 40 rear. Its better than before. I think maybe Im not used to such a light front end. The turn-in is great, its just the understeer while under throttle in the turns.
At 145mph the car was wandering and I had to almost fight it to keep it in line. My last Porsche was ROCK SOILD at this speed and anything under it as well.
Maybe Im just a 928 type of guy....
Former owner of:
1983 928S
1991 928GT
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RL Technical Advisor
Joined: May 2001
Posts: 11,870
Likes: 75
From: Portland Oregon
John:
Your car should not be twitchy at speed,.....!
I just drove a 2001 GT-3 here with 19" wheels and aggressive alignment and it was solid & stable well into triple digits.
I would have your alignment very carefully checked by someone who really knows these cars. These cars should also sit slightly nose-down,....a 1 degree rake is perfect.
Your car should not be twitchy at speed,.....!
I just drove a 2001 GT-3 here with 19" wheels and aggressive alignment and it was solid & stable well into triple digits.
I would have your alignment very carefully checked by someone who really knows these cars. These cars should also sit slightly nose-down,....a 1 degree rake is perfect.