GT4 front camber solutions (for stock ride height)
#1
Thread Starter
Premium Sponsor
Rennlist
Site Sponsor
Rennlist
Site Sponsor
Joined: Apr 2014
Posts: 3,437
Likes: 998
From: Jessup, MD
GT4 front camber solutions (for stock ride height)
The purpose of this post is to inform of the solutions that TPC Racing is using in order to exceed -2.7 degrees of front camber at stock ride height(which we feel is ideal height for dual-purpose, street & track cars to maintain sufficient suspension travel and sufficient ground clearance). GT4's are factory equipped with "split-type" lower control arms. Shims are to be added to lower control arms to gain negative camber. The final amount of camber(which is the angle of the wheels relative to an imaginary perpendicular line from the ground expresses in degrees and fraction of a degree) is a function of the length of the lower control arm via adding or subtracting shims, the adjustment slots on the strut tower, and the car's ride height.
At stock ride height, the amount of shims that can be added to each front lower control arms limits the front camber to around -2.7* with the strut tower adjustment slots at max. * Denoted each car may vary, of course, depending on how the subframes are positioned to the body at the factory assembly line. For those who haven't seen it, below is an image showing the lower control arm and the amount of shims that can be safely added while maintaining the thick washer spacers and two threads protruding the nuts. The thick washer spacers(that are directly next to the nuts) help keep more steady clamping pressure to the studs so its ideal to keep them on.
Having a total of 15mm of shims is safe. I have seen some people use more than 15mm of shims and/or remove the thick washer spacers at their own risk.
One solution to achieve more than -2.7 degrees of front camber is to replace the inner portion of the lower control arm. There are options available from different companies, here in the photo below shows the factory GT3 Cup car inner from Porsche Motorsport. The GT3 Cup car linner is 14.5mm longer than GT4 street car linner. With such length increase, a pair of TPC Racing adjustable thrust arm bushings were used to keep the caster at acceptable range(at below 11 degrees).
Just FYI, the Porsche Motorsport GT3 Cup inners are not easy to get. We had to buy the full arm from PMNA in order to get the inner.
Here's a photo with the TPC Racing adjustable thrust arm bushing(aka caster bushing) installed. You can visualize how the adjustment holes and the position of the holes affect the "reach" of the thrust arm and the affect in caster.
Another solution is to use front camber plates with offset hole for the strut. Here are photos of the stock GT4 street car front top plate compared to an offset top plate(stock GT4 street car top plate is the bare aluminum one)
The replacement of the top plates is straight forward.
With combination of longer lower control arm inners and thrust arm bushings, or offset top plates(aka camber plates), or all of the above, achieving more than -3.0 degrees safely is very possible at stock height. And have plenty of range left to add more!
Because the GT4's have been such a popular car to setup for track use(for all the great reasons!), we've been "borrowing" the Orange color billet aluminum monoball offset top plates from our Tractive 991 GT3/RS coilover inventory. Tractive probably isn't too happy about this but oh well. And the shameless DSC plug.
At stock ride height, the amount of shims that can be added to each front lower control arms limits the front camber to around -2.7* with the strut tower adjustment slots at max. * Denoted each car may vary, of course, depending on how the subframes are positioned to the body at the factory assembly line. For those who haven't seen it, below is an image showing the lower control arm and the amount of shims that can be safely added while maintaining the thick washer spacers and two threads protruding the nuts. The thick washer spacers(that are directly next to the nuts) help keep more steady clamping pressure to the studs so its ideal to keep them on.
Having a total of 15mm of shims is safe. I have seen some people use more than 15mm of shims and/or remove the thick washer spacers at their own risk.
One solution to achieve more than -2.7 degrees of front camber is to replace the inner portion of the lower control arm. There are options available from different companies, here in the photo below shows the factory GT3 Cup car inner from Porsche Motorsport. The GT3 Cup car linner is 14.5mm longer than GT4 street car linner. With such length increase, a pair of TPC Racing adjustable thrust arm bushings were used to keep the caster at acceptable range(at below 11 degrees).
Just FYI, the Porsche Motorsport GT3 Cup inners are not easy to get. We had to buy the full arm from PMNA in order to get the inner.
Here's a photo with the TPC Racing adjustable thrust arm bushing(aka caster bushing) installed. You can visualize how the adjustment holes and the position of the holes affect the "reach" of the thrust arm and the affect in caster.
Another solution is to use front camber plates with offset hole for the strut. Here are photos of the stock GT4 street car front top plate compared to an offset top plate(stock GT4 street car top plate is the bare aluminum one)
The replacement of the top plates is straight forward.
With combination of longer lower control arm inners and thrust arm bushings, or offset top plates(aka camber plates), or all of the above, achieving more than -3.0 degrees safely is very possible at stock height. And have plenty of range left to add more!
Because the GT4's have been such a popular car to setup for track use(for all the great reasons!), we've been "borrowing" the Orange color billet aluminum monoball offset top plates from our Tractive 991 GT3/RS coilover inventory. Tractive probably isn't too happy about this but oh well. And the shameless DSC plug.
__________________
PCA National Instructor
TPC Racing stats:
2023 Porsche Sprint Challenge 992 Cup Am Champion
2023 Porsche Sprint Challenge GT4 Pro-Am Team Champion
2022 Porsche Sprint Challenge 992 Cup & 991 Cup Champion
2020 IMSA GT3 Cup Challenge 2nd Championship
2018 IMSA GT3 Cup Challenge 2nd Championship
2016 IMSA GT3 Cup Challenge Champion
2013 IMSA GT3 Cup Challenge Champion
2006 Rolex-24 @ Daytona GT Champion
2004 Grand-Am SGS Class Champion
PCA National Instructor
TPC Racing stats:
2023 Porsche Sprint Challenge 992 Cup Am Champion
2023 Porsche Sprint Challenge GT4 Pro-Am Team Champion
2022 Porsche Sprint Challenge 992 Cup & 991 Cup Champion
2020 IMSA GT3 Cup Challenge 2nd Championship
2018 IMSA GT3 Cup Challenge 2nd Championship
2016 IMSA GT3 Cup Challenge Champion
2013 IMSA GT3 Cup Challenge Champion
2006 Rolex-24 @ Daytona GT Champion
2004 Grand-Am SGS Class Champion
#2
Ok, I have to ask.
There seem to be guesses floating around that the top camber plates are not sized properly and are a contributing factor to the top strut mount failures. The offset on the adjustable one seems to have the same general foot print but gets closer to the side for even less meat.
There seem to be guesses floating around that the top camber plates are not sized properly and are a contributing factor to the top strut mount failures. The offset on the adjustable one seems to have the same general foot print but gets closer to the side for even less meat.
#3
Thread Starter
Premium Sponsor
Rennlist
Site Sponsor
Rennlist
Site Sponsor
Joined: Apr 2014
Posts: 3,437
Likes: 998
From: Jessup, MD
Ok, I have to ask.
There seem to be guesses floating around that the top camber plates are not sized properly and are a contributing factor to the top strut mount failures. The offset on the adjustable one seems to have the same general foot print but gets closer to the side for even less meat.
There seem to be guesses floating around that the top camber plates are not sized properly and are a contributing factor to the top strut mount failures. The offset on the adjustable one seems to have the same general foot print but gets closer to the side for even less meat.
The purpose of my post is the inform of solutions for camber at stock ride height, this is a very common inquiry that we get so just thought to take the time to share what I know and would prefer to carry on the discussion for this purpose.
Sorry I don't have any facts on your topic of interest. I dare not make any guesses.
#4
Thanks for the great post and information - since we don't want to have to buy a full Cup Arm - are you developing inner's? Or can you share with us who is making these?
Thanks for the information
Thanks for the information
#5
Thread Starter
Premium Sponsor
Rennlist
Site Sponsor
Rennlist
Site Sponsor
Joined: Apr 2014
Posts: 3,437
Likes: 998
From: Jessup, MD
Tarett Engineering and Stomski Racing both sell longer monoball inners, they are referred to as the "RSR/Cup" version.
http://www.tarett.com/items/996-997-...4#ITEM_1619354
https://www.stomskiracing.com/produc...oball-assembly
There may be other companies that'll sell just the inners but these two come to mind first.
I have one new pair of the genuine Cup car longer inners with rubber bushing(exactly as shown in post #1) if you happen to be interested. The rubber bushing is friendier on the subframe. I bought the whole Cup arms and used the outters for a different car. PM me if interested.
#7
Thanks for the write-up!
Hey Tom, the Elephant Racing write-up shows that the 991 Cup Car inner is a monoball: http://www.elephantracing.com/tool-b...Comparison.htm
Is the Cup Car inner you're showing from an older Cup Car (997)?
Hey Tom, the Elephant Racing write-up shows that the 991 Cup Car inner is a monoball: http://www.elephantracing.com/tool-b...Comparison.htm
Is the Cup Car inner you're showing from an older Cup Car (997)?
Last edited by Mech33; 03-01-2017 at 01:36 AM.
Trending Topics
#9
Thread Starter
Premium Sponsor
Rennlist
Site Sponsor
Rennlist
Site Sponsor
Joined: Apr 2014
Posts: 3,437
Likes: 998
From: Jessup, MD
Yes sir. It is standard practice in the industry to interchange 986, 996, 987, 997, 981, 991 control arm/parts. The factory GT4 street car inner has part #991.xxx.xxx.xx on the aluminum portion while the rubber portion has the part #996xxx.xxx.xx. See image below. The factory rubber inner bushing on any street GT3/4, RS, and Cup uses this #996.331.241.04 rubber. This rubber has been serving Porsche factory street and race cars since the early 2000's.
#10
Thread Starter
Premium Sponsor
Rennlist
Site Sponsor
Rennlist
Site Sponsor
Joined: Apr 2014
Posts: 3,437
Likes: 998
From: Jessup, MD
#11
#12
Thread Starter
Premium Sponsor
Rennlist
Site Sponsor
Rennlist
Site Sponsor
Joined: Apr 2014
Posts: 3,437
Likes: 998
From: Jessup, MD
Just for reference, regarding the rear toe setting in post #1, I have received some comments and questions today via email and telephone on this rear toe setting, I wanted to clarify that this amount of rear toe-in in this screenshot is only recommended for use with TPC Racing offset rear toe links. Due to the "less toe'ing-out during rear lift/rebound" characteristic of the rear toe curve as a result of the TPC Racing offset rear toe link design, less "static" toe-in can be set without rear instability caused by toe'ing out during hard braking as the rear of the car lifts. This car just happens to have the offset rear toe links. Whereas with symmetrical(non-offset) design rear toe links more "static" toe-in is set in anticipation of greater toe deviation in the outward direction(toe-out). "Static" meaning at the set ride height with the car not in any kind of motion.
Side note: stiffen springs or stiffen damping on any sort via electronic(DSC) or stiffer mechanical adjustable dampers can retard the rate of movement to limit the rate of toe deviation to sort of band-aid toe'ing out too much too quickly, but too much steady-state stiffness will affect tire grip on compression.
Side note: stiffen springs or stiffen damping on any sort via electronic(DSC) or stiffer mechanical adjustable dampers can retard the rate of movement to limit the rate of toe deviation to sort of band-aid toe'ing out too much too quickly, but too much steady-state stiffness will affect tire grip on compression.