Anir

My 993TT is lowered to RS spec with the PSS-9's, and seems to be suffering from significant bump steer. The car has been aligned by Wright Tuning in Cinci, who has a lot of experience with racing Porsches, so I think the alignment specs should be correct. However, I'm wondering if the nose is too low.

The way the steering wheel jerks over every small road imperfection is driving me crazy, so I would like to install the GT2 evo uprights as shown on Gert's website.

Has anyone else done this specifically for a TT? Do the parts (uprights, bearings, tie rods) vary from a NA model? Any specific recommendations would be greatly appreciated. If I'd be better off simply raising the ride height a bit, please say so.

Air Kuul TT

Anir,

I think JRG (johngordonsenior) had this done to his previous 993TT by Viper Bob. Try giving either of them a PM. Good Luck.

fc-racer

Anir, your tire choice can play a huge role in how the steering feels over bumps. Even temperature plays a big role. When I run race Kumhos or the Pirelli Corsas, the steering is much more lively around the city over bumps. In the cold temperature, the steering is very annoying over bumps with the Corsas, although it's not their fault, they are not supposed to be used in those temps at all. Try changing your tires and see what happens.

Kevin

Anir, I have a spare set of factory EVO uprights, bearings and tie rods.. There are plenty of other suspension experts out there, but when you are sitting that low the angle of your tie rods will create bump steer.

JJB has just mentioned about his custom valving. Jack at Bilstein has my set of Supercup shocks right now..

JJayB

If your getting this feedback on the street, it will be worse on a track. Your too low for your setup and should go to the GT2 evo uprights if you want to keep a low ride height or track the car. These cars are sensitive to ride height. I've replaced mine and it cured the dreded bump steer in turn 8 at WSIR. If you have Pss9's the springs are around 325lbs which isn't too much but it sounds like you have limited shock travel.

Jim Morton

Anir:

I added the GT2/EVO uprights and tie rods to my TT earlier this year. Bump steer had been checked before as well as after the install.

With the EVO upright and the car at RS ride height the tie rod angles are ideal for controlling bump steer.

For everyday highway driving, the change in the steering feel was not super obvious. However, on the track or when driving backroads, the difference in feel is amazingly better. You'll enjoy a lot more confidence in the feel of the steering as you "toss" the car around in turns (Hopefully smooth and fast...)

All this said about the improvement with the EVO uprights, what you descibe sounds more like a Kinematic Toe issue than front end bump steer. When my Kine Toe was off, my car had a bump effect much like you describe. I would say the car is "notorious"... FWIW, some of our cars run out of adjustment for Kine Toe when you are down at RS height.

Given the high weight percentage on the rear of the TT along with the "big meats" for tires, the rear suspension is awefully "powered up" to simply "drive over" the front setup. I think that getting the rear suspension set properly is a very big deal when dialing up a 993TT for good steering feel as well as good handling.

I hope you get ot the bottom of the issue soon. having an awkward handling 993 is certainly a PITA...

My $0.02...

Anir

Hi Guys,

Thank you for the input. Tony, I'll check with JRG and VB. fcracer, it has been noticeable with a variety of tires, including R-compound P-Zero C's, Dunlops Supersports, and now Pirelli Wintersport 240's. I agree that it's more noticeable in colder temps, but it was present in the summer, as well. Maybe, it would be less noticeable with traditional non-R-compound performance tires such as S-03's?

Kevin and JJB, I no longer track this car, but I do like the lower ride height and may consider the Evo uprights, vs. raising the car. I was surprised that the PSS9's bottomed out at 60 mph on the freeway after hitting an admittedly pronounced expansion joint. Therefore, the car may need to be raised (or at least the front nose), regardless of the addition of Evo uprights. Kevin, would your parts be correct for a 993TT? Please feel free to e-mail me at adhir@qx.net with information regarding former use and pricing if you want to sell them. I may be interested.

Thanks again to all. Any other input, particularly from owners with this mod, would be greatly appreciated.

Anir

Jim,

Thank you for the info! I was also wondering about Kinematic Toe, but Wright Tuning assured me that this was correct, and a local suspension shop also subsequently said that the alignment was correct. Unfortunately, I've not found any Viper Bob or Steve Weiner quality Porsche experts in our area.

I think I need to start by raising the height a bit and having it realigned (incl Kine Toe) and corner balanced again. This may keep me from scraping the nose so easily on driveway entrances, and provide the supension with more travel. Maybe, it will also allow better setting of the Kine Toe as you suggested.

Do you think it would still be worth adding the Evo uprights if the car is lowered but not all the way to RS spec? I don't mind the expense if it will make the car handle as accurately as possible. The current handling is certainly a PITA.

Jean

Anir
The biggest change in my car's handling at the front end was the adjustment of the toe settings to 8min. each side. It made night and day difference in fast turns on bumpy surfaces, I have 265 in the Fr and previously needed California Governor's arms to keep the car under control.
My car is about RS height.

Anir

Thanks, Jean. I'll look up my last toe settings. Would you recommend 8min for someone running 245 up front?

Do you have the GT2 Evo uprights/bearings/tie rods on your car?

Rassel

Anir,

Hard to determine what you consider to be a problem, since your feeling is described in writing. However it could be that you have a too aggresive track setup to get it comfortable on the street. Do you still have this problem with 225 in the front? When you look at the wear pattern of your front tires, how do they look?

If you're not tracking the car, perhaps a different setup can solve your problems. Jean mentioned toe setting which can make a car feel nervous on the street.

Could you elaborate a bit about your earlier setup?

viperbob

Hi Anir. Here is a post showing the diff with the Evo front uprights with a PSS9 setup. You can see that at a little over RS ride height, that the control arm is not parallel with the tie rod. In the second pic you can see that they are now close to parallel with the EVO setup. I found it a great upgrade, and sold and installed many of these (including Jim Ms).

https://rennlist.com/forums/showthre...light=uprights

Now the real question is are you going to notice a diff with this setup? As Jean mentioned, for strictly street driving you rarely get an indication you have any bump steer issues. On spirited back roads, and fast on/off ramps you may see it. THere are a lot of folks out there with lowered TTs and NA cars that do not have this setup and are fine. I would get your car aligned / ride height set to where you want it, kinematic toe dial in, etc before going to this level. It is a $2K+ upgrade by the time your done. Make sure you need it first. Oh and the TTs use all the same compnents as the NA cars... I hope this helps. Good luck Anir, and stop by more often....

Anir

Rassel and VB,

I really appreicate your input. Here are the alignment settings from a 2003 printout. Unfortunately, I had a very difficult time getting specific info from Wright Tuning, so I don't have a printout from the most recent alignment. I am pretty sure that the current alignment settings are similar to that below, but they may be slightly more aggressive. I do think the forward rake is a little more pronounced (like Felker's car), and I still wonder if that's a contributing factor.

Front camber: L -1.7, R -1.6
Front caster: L 5.2, R 5.4
Front toe: L 0.05, R 0.02

Front cross camber: -0.2
Front cross caster: -0.2
Front total toe: 0.07
Front setback: -0.03

Rear camber: L -2.5, R -2.4
Rear toe: L 0.15, R 0.16

Rear total toe: 0.31
Rear thrust angle: -0.01

After the shunt at Road America, Wright Tuning replaced the right front and rear wheel bearings, control arms, wheel bearings, and drive shafts, and the right front PSS9 and tie-rod.

Overall, I don't remember the front end being this darty on rough surfaces in the past, even with alignment settings like those above. I don't see any unusual wear patterns. Perhaps, I am noticing it more right now due to the snow tires and unusually cold temps.

As you've suggested, I think the first step is to set-up the car less aggressively, especially since it's a dedicated street car now. What settings would you recommmend? Would a ride height half-way between ROW and RS work well, but eliminate the need for Evo uprights? Again, I don't mind the Evo expense IF it will make a difference, but it sounds like it might not for street driving once I get the ride height and alignment settings addressed.

Any suggestions on specific alignment settings, or should I use the stock Porsche recs? I plan to talk to the newly opened Porsche dealer in town to see if I can work with the mechanic to make sure the Kine Toe is addressed accurately. VB, I wish you were closer than Florida!

Thanks again!

pstoppani

What you describe is not "bump steer", it is "steering kickback". Bump steer is a condition where a bump causes the alignment, typically toe, to change as the suspension compresses. Bump steer is something you notice at high speeds in a corner when you hit a bump and the car starts to take different path.

Kickback is usually a function of the stiffness, or directness, of the connection between the wheels and the steering wheel. Did you update any suspension bushings? Did you go with wider or larger diameter wheels?

You also mention "dartiness. Wide tires make this worse, as do stiffer sidewalled tires. What tire sizes are you running? Generally, the easiest way to reduce dartiness is to reduce camber and go with a street spec toe setting. You may need to raise the car if you can't get the camber where you want it.

I've had my car very low and it did not suffer from either bumpsteer nor kickback. I've since raised it to RS spec and it still has neither malady. My car is setup for aggressive/track driving so I just live with the dartiness.

Anir

Pete,

I admit that I am far from an expert in this area, and bumpsteer has been aggressively debated on this forum for years. However, I have both symptoms that you describe - increased kickback and the tendency for the car to take a different path after hitting surface imperfections in high speed (or slow speed) corners.

When originally upgrading from the stock front 225's to 245's on Fikse FM-10s years ago, I noticed increased road feedback and "kickback". It never bothered me. What I am feeling now is different and worse, and it's still present despite changing back to the stock TT hollowspoke wheels and relatively skinny snow tires (225 front, 265 rear).

Something's definitely wrong that does not seem related to tire width (since it's present with 225 Wintersports and 245 Dunlops or P-Zero C's). Maybe, the sidewalls are stiffer on the R-compounds and snow tires, but it still seems excessive and new to me. The suspension bushings are all stock and my PSS-9's are set to 4-5 (again, the same as in the past with no problems). In my experience, setting the PSS-9's much softer (e.g. 8 or 9) is too soft, even for the street.

Anyone have suggestions on good alignment settings and ride height for the street? I'd like to keep it a bit aggressive, but dial out some of the dartiness. Thanks again!