991 GT3 Suspension Overview
04-08-2014, 01:06 AM
#18
This is an excellent post!
(A nice break from all the stop sale talk).
Great description of the of the suspension.
I was told by a few Porsche mechanics that the main reason that Porsche advises against Slicks on the 991GT3 is nothing to do with the suspension or rear wheel steering. It's because they want you to trade up to a Cup car & all the maintenance issues they had with the previous center locks; what's your opinion of this?
Thanks for starting this.
(A nice break from all the stop sale talk).
Great description of the of the suspension.
I was told by a few Porsche mechanics that the main reason that Porsche advises against Slicks on the 991GT3 is nothing to do with the suspension or rear wheel steering. It's because they want you to trade up to a Cup car & all the maintenance issues they had with the previous center locks; what's your opinion of this?
Thanks for starting this.
04-08-2014, 01:44 AM
#19
Great post. Thank u
04-08-2014, 03:07 AM
#20
Former Vendor
I read the whole thing. This was exactly what I needed to make me be more "forgiving" of the delay. Thank you so much for sharing. If I may, I have a three questions:
1-When I added negative camber to -3, the caster increased significantly as you point out. It increased to a point that the tires were rubbing on full turn and turning in (on the street, not the track) felt less precise. You mention that it would have helped grip; does that apply to track speeds only?
2-Because of the majorly increased caster, we replaced the lower control arm bushings with those from the 996/997 GT3. I had to buy the whole contol arm and extract and subsequently compress the bushings into the 991 lower control arms. You nicely illustrate the 991 bushings as being more rigid. Do you think I am compromising my handling much by changing to the 996/7 lower arm control bushings? All other bushings are left untouched.
3-This is a little redundant but perhaps I'm tryuing to sum up an answer: is it theoretically best to leave the stock bushings, with a negative camber out to a max of -3 and a resultant massive caster that the wheel looks absurdly pushed to the front than what I did? I realize you don't have real data, am just looking for a hypothetical answer.
Thanks again for a wonderful post.
Sam
1-When I added negative camber to -3, the caster increased significantly as you point out. It increased to a point that the tires were rubbing on full turn and turning in (on the street, not the track) felt less precise. You mention that it would have helped grip; does that apply to track speeds only?
2-Because of the majorly increased caster, we replaced the lower control arm bushings with those from the 996/997 GT3. I had to buy the whole contol arm and extract and subsequently compress the bushings into the 991 lower control arms. You nicely illustrate the 991 bushings as being more rigid. Do you think I am compromising my handling much by changing to the 996/7 lower arm control bushings? All other bushings are left untouched.
3-This is a little redundant but perhaps I'm tryuing to sum up an answer: is it theoretically best to leave the stock bushings, with a negative camber out to a max of -3 and a resultant massive caster that the wheel looks absurdly pushed to the front than what I did? I realize you don't have real data, am just looking for a hypothetical answer.
Thanks again for a wonderful post.
Sam
Hi Sam, all good questions.
1- There are two ways to increase camber (a) at the strut top camber plate (b) by extending the lower control arm. Method (a) does not cause an increase in caster angle. Method (b) does increase the caster angle.
The reason this happens with (b), as the lower control arm is lengthened it does not extend straight out. Instead the diagonal member attached to the bushing in the middle of the lower control arm
forces an arc path to be followed. The ball joint end of the lower control arm is drawn forward and caster is increased.
This picture illustrates what happens:
2- The old style 996/997 GT3 lower control arms managed this by have two positions for the diagonal member to attach, thus creating two caster positions and allowing at least a crude compensation for
the lengthened control arm. Note the intersecting holes drilled in the bushing. This is what your car has had retrofit.
Buying those 996 GT3 control arms is really the long way around (read expensive) to getting the caster reducing bushings. We have a product to solve this problem. Our product provides a solid bushing
replacement that is rotatable to provide caster adjustment. It has more range than the 996 GT3 bushes, and is adjustable instead of 2 position limited.
Here is our caster adjuster installed on a regular control arm (non-GT3), but if fits the GT3 front arms too.
The caster adjuster is on our website here
3- It would be best to replace the stock bushings with well-extended lower control arms. As you experienced, tire rub can happen and you likely have excessive caster at that point.
Last edited by Elephant Chuck; 04-08-2014 at 02:12 PM.
04-08-2014, 03:26 AM
#21
Former Vendor
I was told by a few Porsche mechanics that the main reason that Porsche advises against Slicks on the 991GT3 is nothing to do with the suspension or rear wheel steering. It's because they want you to trade up to a Cup car & all the maintenance issues they had with the previous center locks; what's your opinion of this?
On the Cup cars, I expect to see more spherical bearings in place of rubber, no rear steer, bladed swaybars - we'll see.
I suspect there are non-technical motives for the no-slick policy.
04-08-2014, 03:31 AM
#22
Former Vendor
The stiffer rubber bushings are not available separately from Porsche. And with one exception, the rear suspension arms of the GT3 do not fit on the 991.
As an even higher performance alternative to stiffer rubber, we do have available spherical bearings to replace all the rubber bushings on the 991 suspension arms. Info here on the sphericals
The GT3 coilovers will not fit the 991.
04-08-2014, 06:13 AM
#24
I love the detailed differences between Carrera and GT3 suspension components. This makes the GT3 so much more special. Hopefully we'll soon get passed all the BS and start appreciating and sharing our set ups and experiences.
04-08-2014, 12:10 PM
#25
Rennlist Member
Great post, thanks!
04-08-2014, 01:28 PM
#26
Hi Sam, all good questions.
1- There are two ways to increase camber (a) at the strut top camber plate (b) by extending the lower control arm. Method (a) does not cause an increase in caster angle. Method (b) does increase the caster angle.
The reason this happens with (b), as the lower control arm is lengthened it does not extend straight out. Instead the diagonal member attached to the bushing in the middle of the lower control arm
forces an arc path to be followed. The ball joint end of the lower control arm is drawn forward and caster is increased.
2- The old style 996/997 GT3 lower control arms managed this by have two positions for the diagonal member to attach, thus creating two caster positions and allowing at least a crude compensation for
the lengthened control arm. Note the intersecting holes drilled in the bushing. This is what your car has had retrofit
Buying those 996 GT3 control arms is really the long way around (read expensive) to getting the caster reducing bushings. We have a product to solve this problem. Our product provides a solid bushing
replacement that is rotatable to provide caster adjustment. It has more range than the 996 GT3 bushes, and is adjustable instead of 2 position limited.
Here is our caster adjuster installed on a regular control arm (non-GT3), but if fits the GT3 front arms too.
3- It would be best to replace the stock bushings with well-extended lower control arms. As you experienced, tire rub can happen and you likely have excessive caster at that point.
1- There are two ways to increase camber (a) at the strut top camber plate (b) by extending the lower control arm. Method (a) does not cause an increase in caster angle. Method (b) does increase the caster angle.
The reason this happens with (b), as the lower control arm is lengthened it does not extend straight out. Instead the diagonal member attached to the bushing in the middle of the lower control arm
forces an arc path to be followed. The ball joint end of the lower control arm is drawn forward and caster is increased.
2- The old style 996/997 GT3 lower control arms managed this by have two positions for the diagonal member to attach, thus creating two caster positions and allowing at least a crude compensation for
the lengthened control arm. Note the intersecting holes drilled in the bushing. This is what your car has had retrofit
Buying those 996 GT3 control arms is really the long way around (read expensive) to getting the caster reducing bushings. We have a product to solve this problem. Our product provides a solid bushing
replacement that is rotatable to provide caster adjustment. It has more range than the 996 GT3 bushes, and is adjustable instead of 2 position limited.
Here is our caster adjuster installed on a regular control arm (non-GT3), but if fits the GT3 front arms too.
3- It would be best to replace the stock bushings with well-extended lower control arms. As you experienced, tire rub can happen and you likely have excessive caster at that point.
04-08-2014, 01:35 PM
#27
Rennlist Member
Join Date: Feb 2006
Location: Wishing I Was At The Track
Posts: 13,516
Received 1,727 Likes
on
914 Posts
3-This is a little redundant but perhaps I'm tryuing to sum up an answer: is it theoretically best to leave the stock bushings, with a negative camber out to a max of -3 and a resultant massive caster that the wheel looks absurdly pushed to the front than what I did? I realize you don't have real data, am just looking for a hypothetical answer.
http://www.tarett.com/items/996-997-...010-detail.htm
It's a much better solution to caster adjustment vs trying to work with limited adjustment offered by adjustable thrust arm bushings.
04-08-2014, 02:02 PM
#29
Sam: Just get an adjustable thrust arm when they become available for 991. See link for example.
http://www.tarett.com/items/996-997-...010-detail.htm
It's a much better solution to caster adjustment vs trying to work with limited adjustment offered by adjustable thrust arm bushings.
http://www.tarett.com/items/996-997-...010-detail.htm
It's a much better solution to caster adjustment vs trying to work with limited adjustment offered by adjustable thrust arm bushings.
