Spinout

I recently have had a Moton suspension installed on my dedicated track 2004 C2, replacing the stock X74 suspension. New oil overs, springs, adj. drop links all around, and GMG sways were installed.

Tomorrow I’m trailering it to a local race pro shop for a corner balance and full on track alignment before I head to AMP this coming weekend.

Is there any reason I shouldn’t opt for a GT3 cup car ride height (86mm front /107mm rear) vs the standard GT3 ride height (128mm rear/115mm fr) on a dedicated track car?

My main tracks run are VIR, RA and Barber with some AMP, CMP and Sebring thrown in occasionally.

Thanks for the insights.

AudiOn19s

The problem you're going to face with the C2 is the geometry on the uprights is different from the GT3 leading to bump steer issues as you really lower the car. I fought this with my old C2.

I wouldn't go lower than the GT3 settings and even then I'd make sure you have toe links that support bump steer correction and shim the heck out of them.

stujelly

find tim olsen on here. He is a master at this stuff

Krokodil

Lowering the car too far (or much more than 0.8" from stock) will start to mess with the roll center/roll couple. Contrary to popular opinion, lowering a Porsche (or most any strut-based chassis) results in more roll, not less, on the same springs. It also results in a reduction of dynamic camber gain when compressed during cornering.

As stated above, the GT3 and Cup have different wheel carriers that alter the outboard pickup points to allow lower ride height while maintaining nearly the same geometry. In addition to the roll couple issue, lowering the stock chassis reduces the trailing arm angle which creates a shorter moment arm, resulting in a harsh suspension that has a tendency to slide rather dive or squat.

Cheers,

Viperbob1

Also unless you they were Cup shocks they do not have the limiters in them. If you go to Cup height you should have the limiters and if they do have the limiters you cant even get near stock height

Spinout

Welllllllll, Crap.

So what's the best compromise? Lower it less than 1" and the upgraded suspension will still be beneficial? I can add the bump and toe steer arms in the next few weeks.

I will hold off on the corner balance tomorrow being that I still have to add the bump/toe steer components but will need to get it aligned (and aligned again once the bump steer components are added) if I want to drive it at all this weekend.

Thanks to all for the comments.

AudiOn19s

i still went to GT3 height on my old c2. If you're doing the arms in the next few weeks then go where it needs to go height wise and corner balance wise now and just tweak the alignment when you change the arms front and rear to compensate for bump and you'll be fine.

I went lower at like 105 / 125 at one point and the car darted on the brakes pretty badly. I think I settled in around 113 / 128 finally on my old car.

dgmark

My setup is 110mm front and 120mm rear on 650 front 800 Rear springs with GT3 roll bars. A common misconception is to over-spring and set the cars to low.

LostSouth

I have the numbers. I'll send them to you later today

Spinout

Please do send them. I dropped the car off this morning and they'll be working on it today. I'm running 650F/925R springs. The height settings I asked him to achieve are:

Vehicle Height (factory GT3 height)
Front axle height 115 + 5 mm (115 to 120 mm)
Rear axle height 128 + 5 mm (128 to 133 mm)

Front Camber -2.5-3.0^ ( if attainable)
Rear Camber -2.0-2.5 (less 5^ than front)

Toe Front 0
Toe Rear -2.5^

He did tell me I can add the toe/bump steer but he definitely recommends rechecking the alignment once installed. He will also counterbalance the car this afternoon or tomorrow morning. I'll pick it up tomorrow afternoon.

Thanks for all the comments and suggestions. I'm just coming into this galaxy of suspension info and just now that I have a car to actually apply it to, I'm now understanding it all (well, most if it).

jrgordonsenior

Did you buy your new shocks for a street GT3 or a cup car?
Cup shocks have significantly less travel than C2 shocks due to the droop limiters as Bob mentioned along with their shorter bodies and shafts. They're engineered to work with 1400/1500 lb springs.

Your shocks with 650/925 lb. springs need to travel to perform their function so going too low will cause a plethora of issues ranging from bad geometry as Krokodil mentioned to minimal droop which has you riding on the bump stops. Not fun as I can attest to....

If you want lower you need the complete package to make all the parts function along aero front & rear to balance out the car.....

jj1

Has anyone had success using the ERP control arms with the roll center adjuster combined with bump adj toe arms and regular c2 hubs? This seems like a good alternative to sourcing hubs.

Krokodil

Yes, but on a Cayman where the only pick up points are the lower control arm mount and track rod mount, not on the rear of a C2 with the upper control arms (these points wont move). The strut front is the same on both cars and should work fine (although we use the Cup wheel carriers).

Cheers,

jdistefa

^ all good advice above. The only fix if you want to go lower is to run Cup uprights with appropriate pickup points. Oh, and IMHO you have too much rear spring for 650 fronts.

jrgordonsenior

Especially without a real wing. I'm 580/800....