991 GT3 Geo settings. Caster? - Page 3 - 911/Carrera GT - PistonHeads UK

I had my geo set to standard factory settings yesterday. first point is that my 3k mile car was wildly out of shape!!! and second point is that the caster is not adjustable and yet it is considerably out of tolerance. 7.30-8.30 is range and it is 9.19 and 9.29. Thoughts please gentlemen?

5517 said: I had my geo set to standard factory settings yesterday. first point is that my 3k mile car was wildly out of shape!!! No big surprise there I'm afraid, contrary to what most think/expect of a new Porsche GT car, most are out of alignment and the rear ride heights too low/front to rear rake incorrect. The springs will settle after the car is built. I'd to expect to have to do a ride height/geometry check six months after delivery to ensure all is correct 5517 said: And second point is that the caster is not adjustable and yet it is considerably out of tolerance. 7.30-8.30 is range and it is 9.19 and 9.29. Thoughts please gentlemen? See the link to "Caster adjuster" on this page : http://www.elephantracing.com/suspension/controlar... http://www.elephantracing.com/suspension/bushings/... Looks like you'll be kissing your warranty goodbye if you fit them though...... Explanation of Cup car and 991 GT3 caster adjustment/lack of adjustment can be found here : http://www.elephantracing.com/tool-box/specs/991/C...

yes, check ride heights...

Has anyone taken their 991 GT3 to Chris @ Centre Gravity to have the settings reviewed and, if appropriate, adjusted? I'm not sure I've spent enough time with the car yet to seek a particular adjustment, but at least confirming that the settings are within specification would be helpful.

So this was before... and after... The geo settings in the drivers manual show zero toe on front which Im told is very odd. The geo settings direct from Porsche to the geo computer are different. Should i complain to Porsche about the caster issue?

Ride heights weren't checked I presume ?

Surely Porsche have to get your castor settings correct? Whatever it takes?

Slippydiff said: Explanation of Cup car and 991 GT3 caster adjustment/lack of adjustment can be found here : http://www.elephantracing.com/tool-box/specs/991/C... A very interesting discussion, but I thought this comment was most telling: "The two cars are surprisingly very similar to each other as far as the suspension goes. This generation of GT3 is closer to the Cup car than a standard Carrera; closer than previous versions of the GT3. "

5517 said: The geo settings in the drivers manual show zero toe on front which Im told is very odd. Zero toe isn't all that unusual. I run zero front toe on all of my GT cars & it gives you great steering feedback without being too twitchy on the road. Toe out is great on a pure track car but a bit lively for road use! The more toe in you run, the more stable the car is, particularly at speed, but you lose more steering feel & the car isn't so eager to turn in. Set up according to taste. More caster will give you a stronger steering self-centre tendency & can often aid front-end grip due to increasing the camber gain when cornering. The only real downside of more caster is that you will need more steering effort to overcome the self-centreing forces. Your caster is a way past the optimum angle though, so I'd suspect that the car is running lower ride heights than it was designed to. This will have the tendency to increase the caster angle.

Slippydiff said: Ride heights weren't checked I presume ? No this was a simple £80 alignment done as a last minute thing prior to tracking the car for the first time today.

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nxi20 said: Your caster is a way past the optimum angle though, so I'd suspect that the car is running lower ride heights than it was designed to. This will have the tendency to increase the caster angle. Thank you, great input. Where are the "factory" height details found?

Ride height, and the datum points used to set them will be within the technical data accessed on line ? by the technicians. It's downloadable by the technicians, but I think they have to log on to the system using their own unique access code, once they've done so any information they download/print off has their name emblazened across it ..... Where did the above information for the toe and camber settings come from ?

sidicks said: A very interesting discussion, but I thought this comment was most telling: "The two cars are surprisingly very similar to each other as far as the suspension goes. This generation of GT3 is closer to the Cup car than a standard Carrera; closer than previous versions of the GT3. " Hmmmm, where to start ........

It's soo close they don't even need to share an engine

ArcticGT said: It's soo close they don't even need to share an engine What has that got to do with suspension?

ArcticGT said: It's soo close they don't even need to share an engine Or the bodyshell....

Slippydiff said: Where did the above information for the toe and camber settings come from ? page 203 of the drivers manual in your book pack.

5517 said: page 203 of the drivers manual in your book pack. Well you now need to find out what the front and rear ride heights are and the datum points for them.

A friend is an Ohlins specialist, he always comments that Porsche are the worst offenders for incorrect alignment from the factory...

sidicks said: What has that got to do with suspension? Absolutely nothing

So where is a good place to go (Kent/London) to get settings checked? I would like them straight before the season starts OPC? JZM? Elsewhere? Centre Gravity is too far from me to go for such minor tweaks

JZM, Parr or Fearnsport at Silverstone. But personally I wouldn't discount a trip to Chris @ CG on the basis "it's too far to go". I think you'd probably find the day/process quite illuminating.

Slippydiff said: JZM, Parr or Fearnsport at Silverstone. But personally I wouldn't discount a trip to Chris @ CG on the basis "it's too far to go". I think you'd probably find the day/process quite illuminating. Ive heard its well worth making the effort and that Chris is the geo king I used Parr to do the total set up my 996.1 gt3 about 8 years back and they were wonderful. I drove 200 miles to see them. It was a lengthy and i think quite expensive process but the car was superb afterwards.

5517 said: Slippydiff said: JZM, Parr or Fearnsport at Silverstone. But personally I wouldn't discount a trip to Chris @ CG on the basis "it's too far to go". I think you'd probably find the day/process quite illuminating. Ive heard its well worth making the effort and that Chris is the geo king I used Parr to do the total set up my 996.1 gt3 about 8 years back and they were wonderful. I drove 200 miles to see them. It was a lengthy and i think quite expensive process but the car was superb afterwards. Thanks I was at JZM the other day when I got them to fit my sharkwerks and was thoroughly impressed with them. They are only 30 minutes from me so probably suits me quite well although I will give centre gravity some more thought

Scott Parker said: So where is a good place to go (Kent/London) to get settings checked? I would like them straight before the season starts OPC? JZM? Elsewhere? Centre Gravity is too far from me to go for such minor tweaks I'm making the trip from Kent to Centre Gravity in a couple of weeks (when I'm doing my GT3 day at Silverstone) so I'll let you know how it goes.

5517 said: page 203 of the drivers manual in your book pack. 5517 Did you contact Porsche about your car, either: - the discrepancy on the caster settings? - the discrepancy between the settings in the driver's handbook and those obtained direct from Porsche? Thanks Simon

Its with the OPC now having its new radiator fitted that failed on Saturday. Centre core collapsed They are looking at the geo caster issue and will report back shortly.

Thanks - what happened to the radiator and how did you become aware of it? Edited by sidicks on Tuesday 17th February 13:41

sidicks said: Thanks - what happened to the radiator and how did you become aware of it? Edited by sidicks on Tuesday 17th February 13:41 I became aware of it after missing the Marshall's black flag on the start finish straight at Oulton Park for what they thought was smoke bellowing out of the back wheels. 20 seconds later the dashboard went RED and STOP!!!!!!!!!!! I did and you could smell the glycol. It was steam not smoke they saw. Recovered to OPC yesterday and fault diagnosed today, part ordered from Weissach for delivery tomorrow, car back Thursday and straight back to Oulton Park this Saturday. (weather permitting) I am having cruise retro fitted and some rattles sorted while its in

5517 said: I became aware of it after missing the Marshall's black flag on the start finish straight at Oulton Park for what they thought was smoke bellowing out of the back wheels. 20 seconds later the dashboard went RED and STOP!!!!!!!!!!! I did and you could smell the glycol. It was steam not smoke they saw. Recovered to OPC yesterday and fault diagnosed today, part ordered from Weissach for delivery tomorrow, car back Thursday and straight back to Oulton Park this Saturday. (weather permitting) I am having cruise retro fitted and some rattles sorted while its in Fairly major symptoms then!! Hope you get it sorted quickly and successfully!

5517 said: I had my geo set to standard factory settings yesterday. first point is that my 3k mile car was wildly out of shape!!! and second point is that the caster is not adjustable and yet it is considerably out of tolerance. 7.30-8.30 is range and it is 9.19 and 9.29. Thoughts please gentlemen? I competed in the world rally championship, and became obsessive about suspension geometry....it can take hours to get it spot on....but its worth it. The toe and camber settings are critical for vehicle handling, I always considered caster to be a consequence of getting the desired toe and camber. Once we'd got the correct toe and camber, we'd then adjust the ride height to achieve the correct corner weights. In adjusting the ride height, that would often throw out the toe and camber, so we'd adjust that again....and the iteration goes on until its all correct....! can be really frustrating at times.... On your car, I wouldn't be too worried about the caster being out of tolerance, but it would be nice to get it the same both sides. You may find that in adjusting the ride height and corner weighting, you may get the caster to be closer to the factory settings..?

I took my car to CG in October 2014 as I was going to PEC the following day for my 991 GT3 experience (and what a fantastic day it was!) Chris spent all afternoon and part of the early evening with me and was extremely thorough. The tyre pressures and ride heights were the first thing to be checked and were all spot on before any alignment work was undertaken. After adjusting both axles (nothing far out to start with) the caster which had started at 9,20/9,24, ended up at 9,26/9,27. All the camber and toe settings were spookily close to 5517's on the post shown last Saturday (14th Feb), as well as the caster! As has been reported previously the caster is not adjustable and yet factory specs indicate 7,30 to 8,30 ie 1.5 deg less than ours. I tried getting an explanation for the differences through my local OPC but without success. I am not aware of reason to be overly concerned about the excess caster other than it causing slightly more self-centre on the steering (unless anybody can inform me otherwise?), but I do not understand why the factory figures are so far out from what the cars are now showing. Anybody else had the geo checked and found the front caster to be 9,30 or thereby? Finally, as many have already said, a visit to Chris at CG is well worth it. I learnt so much about the car and if nothing else his enthusiasm and knowledge makes the visit a joy. In my case he picked up a faulty o/s rear toe adjuster (the o/s rws motor) which has now been replaced under warranty. This is something that would have never been detected unless I had gone to Chris.

IREvans has it spot on IMV. After doing lots of racing Camber and Toe are the most important, caster less so from a static measurement. Dynamic wheel alignment (bump-steer if you like) can be affected by caster hence it needs to be in range and equal as you can get it. Caster can really important in cars without power steering to ensure the steering effort is manageable and self centering feels "normal". If its out side to side you can get wheel scrub as well A lot of people pretend to understand it and don't so be careful. I read about the subject a lot and have a Maths background and still only understand about 2% of the theory. It becomes and obsession and most cars I drive annoy me as I can feel they are out of alignment A car should always have your body weight and in the drivers seat and half a tank of fuel seat even for basic alignment, you would be surprised how much this affects the geo. CG can tune the car to what you want, many others can put a GEO on they know works, both are good options.

Thanks Jeweller Re the weight issue, the car was full of fuel, and even washer fluid filled, together with weights in the driver seat. Chris emphasised the need for the caster to be equal on both, which more by luck it seems (as its not adjustable), it was.

Taffy59 said: Thanks Jeweller Re the weight issue, the car was full of fuel, and even washer fluid filled, together with weights in the driver seat. Chris emphasised the need for the caster to be equal on both, which more by luck it seems (as its not adjustable), it was. Unequal caster equals inconsistent steering weight from one lock to the other. Many years ago I asked a well known indy (who shall remain nameless) if they could sort out the differing weights from LH to RH lock on my 964 RS. They did a geo set up on the car and professed it fine and sorted. It wasn't, it was no different........ (no real surprise, they were, and still are a complete bunch of f*cking charlatans) So I took it to another Indy (PCT when they were still in Birmingham city centre) who were open and honest enough to admit geo wasn't their "thing". They recommended I took the car to another individual. I did so and when I dropped the car off with him, we discussed the issue. I left the car and two days later got a call from him saying the car was sorted. When I asked him what the issue was, he replied "Oh that's a secret ! !". But he then ventured that the left hand and right hand caster angles were uneven. I collected the car several days later and was blown away by the improvement in the both the steering feel and weight (now consistent side to side) Whilst sorting the caster issue, he geo'd the car. Out of the four RS's I've owned, the car set up by this gentleman (a racer) was the best of all of them. So completely agree with those saying that caster settings are important, and equal caster is just as or more important.

Caster affects steering weight do to the fact the inside wheel is trying to lift the car affectively. If you think about caster angle and imagine the front strut has a stub axle sticking out 90 deg from the strut and draw a line through the strut top and lower ball joint. Then pivot the strut around the imaginary line ie through the strut top and lower ball joint the more laid back or more caster it has the more the inside wheel will be pushed in to the road. This is what gives the steering weight. To be honest I know your caster isn't correct but it is witching 10" of left to right so it's unlikely no very unlikely to be an issue for you. If a manufacture doesn't give us a cross caster to work to 30" is normally considered a good rule of thumb. So you readings are out but I would not loose sleep of that.

"I have my GT3 half-day at Silverstone" Is this just gt3's on track? How can I join in?

5517 said: "I have my GT3 half-day at Silverstone" Is this just gt3's on track? How can I join in? Half-Day at Porsche Experience Centre, Silverstone - Free when you purchase a new car at an OPC!!

Taffy59 said: I took my car to CG in October 2014 as I was going to PEC the following day for my 991 GT3 experience (and what a fantastic day it was!) Chris spent all afternoon and part of the early evening with me and was extremely thorough. The tyre pressures and ride heights were the first thing to be checked and were all spot on before any alignment work was undertaken. After adjusting both axles (nothing far out to start with) the caster which had started at 9,20/9,24, ended up at 9,26/9,27. All the camber and toe settings were spookily close to 5517's on the post shown last Saturday (14th Feb), as well as the caster! As has been reported previously the caster is not adjustable and yet factory specs indicate 7,30 to 8,30 ie 1.5 deg less than ours. I tried getting an explanation for the differences through my local OPC but without success. I am not aware of reason to be overly concerned about the excess caster other than it causing slightly more self-centre on the steering (unless anybody can inform me otherwise?), but I do not understand why the factory figures are so far out from what the cars are now showing. Anybody else had the geo checked and found the front caster to be 9,30 or thereby? Finally, as many have already said, a visit to Chris at CG is well worth it. I learnt so much about the car and if nothing else his enthusiasm and knowledge makes the visit a joy. In my case he picked up a faulty o/s rear toe adjuster (the o/s rws motor) which has now been replaced under warranty. This is something that would have never been detected unless I had gone to Chris. Taffy I'll be there in a couple of weeks when I have my GT3 half-day at Silverstone, but I won't have time for the full CG process, which I understand can take 4+ hours? Instead I am hoping they will just check the current set-up and, where necessary, get things back within manufacturer's recommended settings as far as possible. Did Chris mention any discrepancies between the geometry settings in the handbook and the ones received direct from Porsche (that 5517 referred to above)? I will post my settings on here once this has been completed so we can compare the caster settings etc. Edited by sidicks on Wednesday 18th February 21:13

5517 said: Or if your the 2nd owner you can pay £395 and use your own car for the experience. I will probably see you there It's £550 to use their GT3!

Or if your the 2nd owner you can pay £395 and use your own car for the experience. I will probably see you there

but if you use your own you can get on the day quicker and I quite like the idea of doing it in my car

5517 said: but if you use your own you can get on the day quicker and I quite like the idea of doing it in my car Yes - I'll definitely be going back in my car later in the year!