airiscool

I want to run my car at RS ride height with either Bilstein PSS10 or KW Variant 3 coilovers. I know lots of guys run at RS +10mm or whatever but I want to keep my car low.

How bad will the bumpsteer be? If Porsche delivered the RS at this height I guess they didn't think it was too bad

The 993RS uprights are all the rage but by the time I buy all the parts (uprights, bearings, tie rod ends, calipers, rotors and ABS sensors) it will be close to $3k in parts which seems like a lot to deal with a somewhat minor issue.

sml

Here is my results ... with RS-5mm front and RS+5mm rear ...

https://rennlist.com/forums/964-foru...coilovers.html

Here's a few thoughts & questions ...

Drives great.

I think there is some bump steer but it is very mild & subjective and doesn't worry me at all.

Bump steer seemed to reduce after I bolted on my wider 18" wheels and had an alignment.

Does minimal bump steer affect performance? Most tracks are relatively smooth so at least on the track, there is no bump steer in my case.

I dont expect the car to drive like a SUV. If I hit a large pothole in an SUV and feel the wheel 'steer' is that bump steer? Is it a problem? You can probably get bump steer on any car if you try hard.

I think bump steer is somewhat subjective.

Would a 964 with 600lb springs at US ride height have bump steer? I guess you could probably feel something at that ride height also if you hit a decent bump.

Are the spring rates ok on the PSS10 and KWV3? What are you using the car for? I have no problems using my 450/600lb springs for everyday driving with the shocks softened.

Watch out for clearances with wheels/tyres/offsets if you are going low.

If tyre clearances are tight, then get stiffer springs. ie with my setup & softer springs, I think would have problems with the tyre hitting the guard under load.

Make sure your coilover selection can actually lower your car to RS height.

sml

Interestingly, I just read my thread in that link above and i said there was no bump steer.

Now I think there is mild bump steer.

Guess that shows it is subjective and it is very minimal so I'm not even sure if it is bump steer.

When I read about the bump steer issue, it read in the threads like it is a major issue and you either have it or you dont. But that's note the case. The car wont explode. Mine drives great and performs well on the track. Maybe there is no bump steer, but maybe there is. Not sure.

The 964 was still completely driveable at RS-10mm and 600lb springs.

Just had a thought ... the spring rates must make a difference!

Soft 300lb springs might compress say 30mm during load or a bump/cornering.
Hard 600lb springs might compress say 15mm during load or a bump/cornering.
So the bump steer must be worse on the softer springs!
Maybe that is why some (like me) would be happy to have the car at RS-10mm with 600lb springs whilst others have complained about RS height with 300lb springs.

Maybe the guys that complained about bump steer at RS height had softer springs?

Geoffrey

My street car is at RS ride height and alignment specs and I drive it every day. There is some bump steer, but it is minor. I have only HR Reds and Bilstein HDs, so the suspension travel will be greater than with the spring rates in the above posts.

airiscool

Valuable feedback from a real racer and tech guru! If you don't mind me asking what is your street car?

Is your opinion that the Evo upgrights aren't required at 964RS ride height unless one is attempting to build the ultimate track machine?

Regulatori

So HR reds and standard Bilstein HD's will get you at euro RS ride height?

I was considering coilovers but may go that route instead.

Geoffrey

My daily driver is a stock black 1992 C2 (except for the aformentioned suspension).

If there are better parts available, then the car will be better, right? So, I suppose the question you are asking is what are the value of GT2 Evo uprights? For a stockish car at RS ride heights, the stock suspension components are fine for the street. If you are going to track the car, then you'll want more agressive alignment settings, and stiffer springs which will then get you into the area where the 964 suspension geometry becomes a hinderance and you may want to consider GT2 Evo uprights. If you don't have power steering, and you begin to lower the car beyond RS ride height, and / or use the first two holes in an RS sway bar, then the car is not enjoyable to drive, especially with the narrow body suspension position used on the C2. Personally, I like the power steering rack and use an electric power steering pump with them on most race cars. It really helps and I think it gives better feel than a non power steering car because you aren't "muscling" the car around.

My race car does not have power steering, however, it has all of the modifications - widebody suspension, correct blade adjustable sway bar, GT2 uprights, relatively narrow front tires on 10" wide rims, and is extremely light at 2200lbs with full fuel. If it were any heavier, or used different suspension, I would have installed power steering.

HR Reds and standard Bilstein HDs will allow for Euro RS ride height. It also makes for a good every day ride, but not so great for the track beyond a novice run group or skill level.

airiscool

More great info What changes between the narrow body C2 and a widebody C2T or America Roadster?

Geoffrey

All 964 widebody cars, and 993 race cars (RSR, GT2) and 993 911 GT (GT2) street car have the suspension side members installed on the outboard position which widens the track about 25mm per side. This requires different tie rods, sway bar, movement of the orientation of the dampers, brake hoses, and may be others I'm not thinking of at the moment.

If you look in your trunk by the ABS pump you can see the chassis to suspension member mounting holes. There are 3 of them, with the suspension member bolted to only 2 (inner and middle for C2), (outer and inner for C2 Turbo).

It makes a noticable difference in handling due to the scrub radius changes.

Turbohead

He told me...... so what he says for sure!!
no bumpsteer here.
Elliot

airiscool

Are you saying that 964 WB models are less prone to bumpsteer than the NB models? The WB cars have better front geometry?

Geoffrey

The 964 WB will have worse bump steer than a NB due to the fact the tie rod is longer so it moves a greater distance for a give compression or rebound of the damper. A WB with correct front suspension position mounting has much better geometry than a WB with the front suspension left in the NB position.

christallon

Hi Geoffrey,

So if you wanted the next step up from the Reds and Bil HD's, where would you go? I want something I can drive on the street, but also to enjoy on track in the more advanced run groups, 3-4 track days a year. Are the KWV3 coilovers the next step up, or is there something in between that will suffice. Costs for Reds/Bil HD's is approx $1,100 materials only. KW's are approx $2,300 materials only. What do you think? The KW price range is really above where I'd like to go if I can find a happy medium a little less costly. It does not need to be adjustible, however due to what I'm looking for, maybe this is the best alternative.....Hmmmmm???

To give you an idea, I loved the stock GT3 suspension on my 04. I could drive that car all day long and be very satisfied. If there was something like that, in an affordable range, I would be happy. Thanks so much for your valued input.

Chris

SuperUser

JIC had one set left at $1800 about a month ago. I did not want to run spring rates that high for a street only / wife car.

Geoffrey

Honestly, I don't really have a good answer for you. I deal mainly with racing cars, so that is where my knowledge is - Moton, JRZ, Ohlins double/triple type setups. The only reason my street car has the HR Red and Bilstein HDs is that they were removed from the doner car turned into my race car. Seemed like an easy an inexpensive way to get rid of the 4x4 stock ride height in my stock car.

With that said, we've installed the JIC Cross suspension in two of the street/track cars and they were surprisingly good on the street after some tuning, but I never had a chance to drive them on the track and cannot comment.