Good evening guys,

I purchased an ’04 GT3 last week with some great upgrades already done. The car has Euro seats, a roll bar, harnesses and the center console delete as well as JRZ shocks and ERP suspension links. I intend to use the car for DE events and possibly some club racing.

On the previous owner’s recommendation, I had the car aligned and have some questions as a result. The Castor is set very low at 6 degrees. It doesn’t appear to be adjustable, at least not by an eccentric. We set front Camber at 2.9 degrees. There was already a 7 mm shim in the front control arm. I found the Kussmaul settings on this forum and used them as a guide. Front and rear toe were set according the Kussmaul settings. Rear camber is set at 2.5 degrees. As the shop didn’t have scales, I didn’t want to mess with ride height. The rear ride height was comparable to the Kussmaul settings, however, the front ride height was significantly lower at 102 mm.

Questions/Concerns.
Would you be concerned about the front castor setting and if so what would you do to fix it?

The rear suspension upper links are ERP adjustable links. Is this a recommended method for getting the rubber out of the suspension? If the lengths are incorrect doesn’t this have a profound effect on Kinematic toe? What have others done?

What ride height do other track oriented GT3s commonly employ?

Thanks in advance for all your replies,
Hank

PS. I look forward to contributing to this great forum!

 

Can't help you with any of those questions but just to say welcome aboard. Looks like you've got a great car.

Zed

 

The factory caster specifications are:

8° +/- 30' ==> (7.5° to 8.5°)

A 6° value looks suspicious to me. Especially, considering that when using 7mm shims, the caster value increases. In my car it would get to 9.2°.

The Manthey Racing camber plates increase caster by 1° over stock, for better straight line stability.

Additionally, you should not be able to get -2.9° camber with 7mm of shims, unless the strut tops have been rotated.

Regarding the rear ERP upper links, I would not make any adjustment to them. I installed similar units in my car, and I set them to the same length as the stock parts. They improve the handling by removing 8 rubber bushings, but once you start playing with lengths, you will compromise the suspension geometry. Only a professional race shop can play with the length of those links, to increase track, change effective spring rates, alter suspension travel, etc.

If you're running stiffer springs at the rear on the 800 lbs or more range, you can safely drop the car 10mm from stock. I dropped mine 20mm below stock, and I was recommended to increase the ride height by Jon Groom Racing, unless I changed the rear subframe and uprights.

Check the alignment at another shop to isolate a possible alignment equipment out of calibration.

Enjoy the car...

 

Zed:
Thanks for the welcome!

NJ-GT:
Thanks for the information. Looking through the documentation that came with the car, I find no mention of aftermarket monoball strut tops. Possibly a bad assumption, but I would think that means the car has stock strut tops and they likely have been rotated. In your opinion, would that and the low front ride height explain the relatively low front castor setting?

I completely understand what you are telling me about the upper links. As a long time 993 racer, one of the upper lengths was adjustable and if it was wrong you were in for a very frustrating weekend.

I believe the car has 600 lb springs up front and 750 lb springs at the rear. Additionally there are tender springs as well. It looks like they are 150 lb up front and 250 lb at the rear. I believe the alignment measurements are correct as they correspond to the set-down sheet I received with the car.
Rear ride height is set to 124 mm which is within 4 mm of stock. The front is at 102 mm which is about 13 mm or ½ inch lower than Euro stock. Is the lowered front a common practice or is that something that just shouldn’t be done?

Thanks again,
Hank

 

Hank,

When I have rotated my stock camber plates, my caster has been reduced by 0.5°. Lowering the front will actually increase caster, as the strut top is behind the vertical line from the wheel carrier center. Adding shims to the lower control arms will increase caster even more, because the control arms get extended and moved forward as you add those shims.

Unless you're running aftermarket camber plates, the only justification for such lower caster number is a front impact, which would move the lower body front pick-up points backward.

So, if you still have the stock camber plates, which is easy to check by removing a front wheel and looking underneath strut top, then you should re-check the alignment at another shop. If you're still getting a 6° caster value, I would measure the distance from the center of the front wheel to the center of the rear wheel, and compare that value against another GT3. If those value are different by a few mm, then check the unibody on a chassis repair shop.

The springs rates are ok for a DE car. I'm running 750/1000 with 150/250 tenders. Last year I ran 450/650 with the same tenders, it was good for autocross, but I was lifting my front wheels too much on track days and fast autocrosses.

The ride heights are ok. 124 is fine, and with those spring rates you can go down to 118mm, beyond that it gets tricky unless you run very stiff spring rates as I was recommended if I wanted 108mm at the rear.

The US cars came at 125mm at the front. The Euro cars came at 115mm, so most of the guys went down to 115mm. 102mm is pretty low, my car is set that low (105mm), and I have some bump steer at the front axle, even with the 750# springs. It can be fixed by switching the uprights to the 996 RS or Race RS/RSR, or installing the cup toe links and spacers at the front steering rods.

Unless you're at the top of the driving skills, front bump steer is not that annoying. However, rear bump steer is really scary.

Do a search on tarret or cup toe links. They are helpful.



Rad