Tom@TPC Racing

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.

ExMB

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.

Tom@TPC Racing

These offset plates have the same bolt pattern and shape as GT3/GT4 street car and GT3 Cup and GT4 CS. They fit perfectly. When the fasteners are tighten properly the load is distributed pretty evenly throughout the plate.

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.

supercup

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

Tom@TPC Racing

My pleasure!

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.

Hams955

Thanks for the information; nice write-up!

Mech33

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)?

zmon

Tom,

Thanks for the great really informative and clear post!!

Z

Tom@TPC Racing

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.

Tom@TPC Racing

Glad to be of service.

trebien

Geez, I'm surprised there's not more little accidental baby Porsches running around.

Tom@TPC Racing

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.

Knolow

Hmm that car looks familiar!

Hams955

Does camber change on the car if static ride height is set lower? IE - possible to get more camber at a lower height?

Yargk

Thanks for the pictures, it's good to have clear images and explanations. I was just under my car today staring at various bits and making sure everything is still tight.