GT3 issues
10-13-2003, 09:53 PM
#1
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GT3 issues
My recently acquired '99 GT3 constantly wanders about at highway speeds (100-140 kph) as if buffetted by cross winds. Two alignment checks done, one to manufacturer spec the other to track day spec have not changed the directional stability at all. It is not bump steer but it feels like the rear of the car is affecting the steering - it also tends to torque steer on & off power at speeds over 100kph. Car runs new Pirelli P Zero Asimmetricos at factory pressure 31/37 psi. Does anyone else have a similar experience or is this a natural Porsche trait??
Second issue is the ABS seems over eager, i.e. the brakes (fronts I feel) are locking very easily. Pads are Padgid RS 4-2 ("blues") front & rear, discs are in good order. Car pulls up nice & straight even from over 230kph on the track but I feel it should stop shorter without lock up. Any comments appreciated. Thanks.
Second issue is the ABS seems over eager, i.e. the brakes (fronts I feel) are locking very easily. Pads are Padgid RS 4-2 ("blues") front & rear, discs are in good order. Car pulls up nice & straight even from over 230kph on the track but I feel it should stop shorter without lock up. Any comments appreciated. Thanks.
10-13-2003, 10:59 PM
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Again I defer to Weng - he will know. This sounds worse than his mk1 GT3 though - did you just get the car? Where did you buy it? Did you check the history and vehicle with a paint thickness meter to be sure the car was never hit hard? Hopefully it is clean and you just need some adjustments.. Good luck!
10-13-2003, 11:05 PM
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Some things to try:
- Double check wheel alignment, especially toe. 40/60% locking LSD combined with bad alignment could cause torque steer,
- Try reducing rear tire pressure to equal front,
- Swap tires and wheels with another car to see if tires are a problem,
- Try Pagid RS19 or the OEM P90-2 yellow. The OEM pad's compound in particular is adjusted slightly to Porsche ABS.
- Double check wheel alignment, especially toe. 40/60% locking LSD combined with bad alignment could cause torque steer,
- Try reducing rear tire pressure to equal front,
- Swap tires and wheels with another car to see if tires are a problem,
- Try Pagid RS19 or the OEM P90-2 yellow. The OEM pad's compound in particular is adjusted slightly to Porsche ABS.
10-13-2003, 11:35 PM
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Greetings,
The wandering you describe in my opinion is too much toe out for the street. On the racetrack less toe in is prefered. Your second problem with the abs sounds like the tire pressures are a little too high and too far apart front to rear. Coupled with the firm suspension the ABS will come on sooner. Although I do not have any time on Pirelli tires, they have been known in the past to be hard. I have not heard any complaints on the Michilens.
I had alot of time on your two issues when I set up my older Carrera Cup car. I would also try Pagid orange pads. I had the best luck with them.
Best,
Don
The wandering you describe in my opinion is too much toe out for the street. On the racetrack less toe in is prefered. Your second problem with the abs sounds like the tire pressures are a little too high and too far apart front to rear. Coupled with the firm suspension the ABS will come on sooner. Although I do not have any time on Pirelli tires, they have been known in the past to be hard. I have not heard any complaints on the Michilens.
I had alot of time on your two issues when I set up my older Carrera Cup car. I would also try Pagid orange pads. I had the best luck with them.
Best,
Don
Last edited by 9caregiver; 10-15-2003 at 10:56 PM.
10-13-2003, 11:38 PM
#5
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Originally posted by RENNMAN
The wandering you describe in my opinion is too much toe in for the street. On the racetrack more toe in is prefered.
The wandering you describe in my opinion is too much toe in for the street. On the racetrack more toe in is prefered.
10-16-2003, 01:11 AM
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Colin,
You may have just purchased my previous car!
Just kidding. What you're describing sounds all too familiar. The mk1 suspension is ultra sensitive to road undulations and camber changes (as are most stiffly sprung low riding cars as I understand it). At highway speeds (and higher), I often felt like the car was constantly getting blown around in the wind. Lifting off the throttle would also cause the car to feel light and wander around a bit. I have the following suggestions which I hope you find useful :
1. OEM cold tire pressures I believe are 2.2 bar (32psi) F / 2.7 bar (39psi) R. You may want to try this for a start.
2. If your car's suspension setup has been changed from stock - as mine was, I found that reducing the rear pressures to 2.5 bar (c.35/36psi) helped to stabilise the car (camber -2F/-3R, toe in 0.1 deg F/R). Kept the fronts at 32psi cold.
3. As others have suggested, check the toe settings on your car. The 0.1deg toe in setting that I have is stock.
4. On fast backroads or highways with surface imperfections, I've learnt to ease up on my grip on the steering wheel and allow for a bit of play. The car seems to be happy to somewhat correct itself and only minimal steering inputs are required to keep it tracking in the desired direction.
Note that the car will never feel as stable as an S-class on a highway but a few tweeks here and there will help. If the wandering is excessive, do check to ensure that the car has not sustained any previous suspension damage.
As for brakes, I found the mk1's stock pads to be useless on track. I tried both the Pagid Orange and Blue. Both work well on track with the Orange being a slightly higher friction compound. I suspect what you are discovering (baring any faults with the ABS controller in your car) has to due with the bite of the race pads overcoming the available grip that you have from the street tires. When I had the Blue pad/street tire combination on track, I found it easier to trigger the ABS and even chirp one of my front tires under hard braking. If you plan to track your car a fair bit, I recommend an investment in a set of r-compounds or street legal semi-slicks. The better dry grip helps not only cornering but improves braking distance by a noticeable margin.
Note that I am no expert and what I have communicated above comes purely from trial & error and lots of advice from other experts on this board. Welcome to the world of GT3's and enjoy the car!
You may have just purchased my previous car!
Just kidding. What you're describing sounds all too familiar. The mk1 suspension is ultra sensitive to road undulations and camber changes (as are most stiffly sprung low riding cars as I understand it). At highway speeds (and higher), I often felt like the car was constantly getting blown around in the wind. Lifting off the throttle would also cause the car to feel light and wander around a bit. I have the following suggestions which I hope you find useful :1. OEM cold tire pressures I believe are 2.2 bar (32psi) F / 2.7 bar (39psi) R. You may want to try this for a start.
2. If your car's suspension setup has been changed from stock - as mine was, I found that reducing the rear pressures to 2.5 bar (c.35/36psi) helped to stabilise the car (camber -2F/-3R, toe in 0.1 deg F/R). Kept the fronts at 32psi cold.
3. As others have suggested, check the toe settings on your car. The 0.1deg toe in setting that I have is stock.
4. On fast backroads or highways with surface imperfections, I've learnt to ease up on my grip on the steering wheel and allow for a bit of play. The car seems to be happy to somewhat correct itself and only minimal steering inputs are required to keep it tracking in the desired direction.
Note that the car will never feel as stable as an S-class on a highway but a few tweeks here and there will help. If the wandering is excessive, do check to ensure that the car has not sustained any previous suspension damage.
As for brakes, I found the mk1's stock pads to be useless on track. I tried both the Pagid Orange and Blue. Both work well on track with the Orange being a slightly higher friction compound. I suspect what you are discovering (baring any faults with the ABS controller in your car) has to due with the bite of the race pads overcoming the available grip that you have from the street tires. When I had the Blue pad/street tire combination on track, I found it easier to trigger the ABS and even chirp one of my front tires under hard braking. If you plan to track your car a fair bit, I recommend an investment in a set of r-compounds or street legal semi-slicks. The better dry grip helps not only cornering but improves braking distance by a noticeable margin.
Note that I am no expert and what I have communicated above comes purely from trial & error and lots of advice from other experts on this board. Welcome to the world of GT3's and enjoy the car!
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10-16-2003, 07:55 AM
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Thanks for your advice guys, much appreciated. I bought the car from the Porsche distributor in Melbourne, Australia(factory owned).The previous owner is a friend of a friend and as such, gave honest answers to questions. No accidents or mechanical problems but he tried a variety of pads so I assume he had similar problems with modulation & bite. He used the car as a daily commuter & ran R tyres, not sure which brand, and didn't have any issues with the directional stability. I tried Weng's & mds' suggestion & lowered tyre pressures to 30/34 which has improved the ride (of course) but only marginal change to stability. I have the car booked in next week for an experiment with another set of wheels & tyres (Oz wheels with Pirelli Corsa's) & another check of the rear toe in. I think my problems are essentially setup issues & know what Weng means with the pads exceeding the grip of the tyres, sticky round black things are on e way. My other car is a Nissan Skyline GTR with 430bhp, uses Pagid RS4-2 for daily use & a swap to RS19 (fronts only) for track days & runs on Bridgestone R's. Coming to terms with the GT3 after a front engined four wheel drive, four wheel steer 1600Kg animal is indeed a challenge requiring a big re-think of technique.
So far my black on black beast & I have a love-hate relationship - love the noise, love the grunt, love the looks but the jury is out on the rest. Great to have a facility like rennlist & lots of experienced participants offering sound advice.
The battle continues, I will win this beast over!!!!
So far my black on black beast & I have a love-hate relationship - love the noise, love the grunt, love the looks but the jury is out on the rest. Great to have a facility like rennlist & lots of experienced participants offering sound advice.
The battle continues, I will win this beast over!!!!
10-22-2003, 10:22 AM
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Good news on the "GT3 issues" topic: I bolted on a borrowed set of P Zero Corsas & the problem disappeared. I have now discovered this is not unknown with Asimmetricos & seems to affect GT3s more. I have a friend who had the same problem with an F40. Thread block squirm is thought to be the culprit but batch variations may be involved as fitting a new set of Asimmetricos may also bring about a cure. Weird stuff. Has anyone else experienced or heard of this??
Also, despite the 225/40 size of Corsa appearing on the Pirelli product list, the 225/40 is not available here in Australia but the 235/40 is. Does the slightly bigger size affect braking or handling? My tyre dealer has also suggested 295/30 for the rear - the circumference is greater & may affect the gearing, ride height & speedometer reading. Any comments??
Also, despite the 225/40 size of Corsa appearing on the Pirelli product list, the 225/40 is not available here in Australia but the 235/40 is. Does the slightly bigger size affect braking or handling? My tyre dealer has also suggested 295/30 for the rear - the circumference is greater & may affect the gearing, ride height & speedometer reading. Any comments??
10-22-2003, 04:29 PM
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Bigger rubber on the front should improve stopping (more braking before ABS kicks in). More front end grip should reduce understeer also.
Re: rear tyre circumference, what is the percentage change?? It will have an effect on all those things, but it will probably not be noticable, depending on overall diametr/circumference change.
Re: rear tyre circumference, what is the percentage change?? It will have an effect on all those things, but it will probably not be noticable, depending on overall diametr/circumference change.
10-22-2003, 05:25 PM
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Pirelli Problems
I had exactly the same problem with my Mk1 GT3 when I chanaged the rear tyres for the first time.
It felt as if the pressures were too low and the tyres were "squirming" on the rim, very offputting.
I contacted Pirelli and they sent a tyre engineer to visit me and check the car over fully.
Whilst there was nothing obviously wrong he recommended that I change the front tyres and arranged for this to be done at Pirelli's expense.
The problem was still apparent after the fronts had been changed, I was asked to give it a few hundred miles to see if it improved as there is referance to the car feeling a bit odd after changing tyres in the owners hand book.
After a further 300 Miles there was no improvement, Pirrelli once again sent an engineer to my home to inspect the car.
After testing the tyres he concluded that he would need to conduct a more detailed analysis which could only be done at the factory and arranged for a complete set of new tyres to be fitted, again at Pirelli's expense.
I did not experinace the same problem with the new tyres so thought it must be an isolated incident as I did not hear back from Pirelli with their findings.
In conclusion, I can not praise Pirelli enough for the way they dealt with my problem and would recommend that you contact them to help resolve your issue.
Hope this helps.
P
It felt as if the pressures were too low and the tyres were "squirming" on the rim, very offputting.
I contacted Pirelli and they sent a tyre engineer to visit me and check the car over fully.
Whilst there was nothing obviously wrong he recommended that I change the front tyres and arranged for this to be done at Pirelli's expense.
The problem was still apparent after the fronts had been changed, I was asked to give it a few hundred miles to see if it improved as there is referance to the car feeling a bit odd after changing tyres in the owners hand book.
After a further 300 Miles there was no improvement, Pirrelli once again sent an engineer to my home to inspect the car.
After testing the tyres he concluded that he would need to conduct a more detailed analysis which could only be done at the factory and arranged for a complete set of new tyres to be fitted, again at Pirelli's expense.
I did not experinace the same problem with the new tyres so thought it must be an isolated incident as I did not hear back from Pirelli with their findings.
In conclusion, I can not praise Pirelli enough for the way they dealt with my problem and would recommend that you contact them to help resolve your issue.
Hope this helps.
P