Falcondrivr

I'm looking at some suspension upgrades for my 993 C2 DD. I want it to be a good DE car, but don't want to ruin it for daily use.
I took an instructor out for a run last weekend and he basically said that I'm driving at or very near the limit of my equipment. He suggested I maybe get some R compound tires.
However, my car just rolled over 152,000 miles (on the track at Sebring Saturday,) and I'm reticent about putting tires on that will generate more forces on the suspension without "freshening" it up a bit. So I'm looking at bushings, adjustable camber plates, monoballs, drop links, strut brace, etc...
I already have the M030 springs and Bilstein HDs, but stayed with the M033 sway bars.
Who's got some good experiences with a nice track/DD 993 setup?

TheOtherEric

Realize that it's ALL a compromise, so every second you go faster on track is a crappier ride on the street (except for running grippy tires on track). You truly can't have it both ways.

Just get some DOT-R tires and you'll be fine. No need to "freshen" up your suspension unless something is worn/broken.

I wouldn't bother with camber plates because you can get enough camber without them (typ 1.7 to 2.0 deg which is fine for a dual purpose car).

Also definitely get a strut brace. Do NOT do monoballs. RS engine mounts is a good move too.

I'm running Motons with 600/800 springs, -2.7 deg camber, RS ride height, and in the process of trying to find ways to make my car more streetable. Plan is to soften the springs, run less camber, and raise the car to reduce the horrible bump steer.

You may be interested to know that my fastest lap times ever on one track I visit were done on PSS9 shocks without camber plates or any other suspension mods. Pretty easy to ruin your ride quality for marginal benefit.

KOAN

I liked the Moton set up that Eric has now. I also had PSS9s before, but liked the Motons much more...enough to justify the cost difference. With Motons 600/800, the street ride is not as comfortable as with PSS9s set on "0". So, if you want a better street ride and OK track ride, PSS9s are the way to go. If you want OK street ride and better track ride, go for something a little more adjustable and stiff.
Eric, Evo upright$ will get rid of bump steer..

jaholmes

You may want to check out the KW Variant 3. They are double adjustable and a little more reasonable prices. All the options above are easily $5k. Where the KW's are closer to $3k.

PSS9'/10's would not be on my list given the KW V3 option.

There are also cheaper bump steer options but just using ERP links in the back.

You may need to do camber plates but have them set to zero. Then you use the ride heigh to get the desired camber.

Flying Finn

I have PSS-9s with camber plates & monoballs and think this is pretty good for street and quite ok for a track also. If I had the money, I'd get Motons though.

I think I need to start replacing all the bushings in my suspension, mainly because I want more precision, less softness. I only have 60K miles but at 150K miles you have, I think you must have some very worn out bushing that would make a difference when changed to something stiffer, even if just stock but new although I'd definitely do some upgrading while changing them.

Bill Verburg

What you have is a good street setup but way too soft for good track performance.

RoW M030 springs are in the F:150/200# R:225/275# w/ a f/r ratio of 0.727

Cup cars used F:600(+tender)# R:800(+tender)# w/ a f/r ratio of 0.75 but also used 245/280 tires to tame the understeer

I'd aim for a ratio in the high .6x range to try to tame some of the understeer.

the Cup springs w/ Motons are very streetable

for more of a compromise 450/675 f/r ratio .67 is very good any of the adjustable shocks that can be dialed back for street use will be fine

RS adjustable sways are nice too

monoballs at the shock tops and toe links w/ locks are very streetable, as are solid side mounts in back. For a street car that sees track use I'd use all RS harder rubber bushes for all the other spots(4 front, 6rear)

also plan on RS uprights/tierods

8/10 w/ 225/40 & 265/35 is good 8.5/10 w/ 245/35 & 280/30 is better

TheOtherEric

Do you have any experience with that? I'm considering dropping the springs to around there, but this would be very overdamped for street driving, so I'm not sure how well it would work out. Plus the fact that the shocks will be getting quite a workout under those conditions.

Are RS spindles different from GT2 spindles? I didn't even know such a thing existed. I assume that would solve the bumpsteer issues but I fear the price tag.

It's funny - one year with an M3 race car and I'm expert on its suspension but I still don't know jack about proper 993 suspension setup...

Bill Verburg

yes, i'm currently on the 3rd iteration of suspension
my car had RoW M030 springs and sways when I bought it, this was a great street setup but miserable on a track.

Next changed to JIC 400/560, still too soft

currently I have the 450/675 mentioned above. This seems about right, at least untill it becomes a dedicated track car. But as mentioned I have friends that have 600/800 w/ Motons that are also street driven


yes, RS and GT2 wheel carriers/uprights are the same parts(993.341.157.81/993.341.158.81 you also need at least the outer RS steering arms, you can use either stock inners or the GT2 monoball inners)), I added them after the JICs went on and the car was lowered to it's current ride height. Yes, they cure bump steer and yes they are expensive

TheOtherEric

Bill - thanks! I think I'll try out your spring combo. But instead of dropping the money on new spindles & tie rods, I'll just raise the ride height. I've eventually learned that you simply can't run RS ride height with stock spindles due to the bump steer problems, so something has gotta change...

jaholmes

Bill, are the springs you are using JIC. Would you happen to remember in kg what the spring rates are. I have 10kg and 14kg and i'd like to go a little softer.

Bill Verburg

1st set was 7/10, too soft
current are 8/12, I've been pretty happy w/ these

bavarian06

Bill, can you dive in more detail what you mean by the ratio of the f/r springs? What is an optimal ratio and why? Correct me if I'm wrong, with a tender spring, it actually lowers the overall spring rate?

The cup cars ran 600/800 but their cars weigh a lot less than our street cars, wouldn't you have to dail it up to take into account of that?

TheOtherEric

There are 2 main issues with relative front-to-rear spring rates. The first is to select them to minimize pitching oscillations caused by bumps. This gives you a much stiffer spring in the rear (for a 993). IIRC, the concept is to run a slightly higher natural frequency (+10%?) in the rear for any street car. I believe this would imply a ratio much lower than 0.75. This is purely a street comfort issue and only relevant for highly underdamped and undersprung suspensions (i.e. street).

Second issue is that of balance (i.e oversteer or understeer). For racecars, this is the only issue that's relevant and people often use splits like 600/800 based on experience.

I came to the same conclusion as Bill, but he seemed to be mostly considering tire issues which is probably most important.

p.s. this has nothing to do with tender/helper springs. For motons, we use low-rate springs that are 100% coil bound when loaded, so they don't affect the overall spring rate.

bavarian06

I seriously need to pick up a book on race car setup.

This is my current setup.

Front 1.75" 150lb tender matched with 6" 950lb main
Rear 1.75" 150lb tender matched with 5" 1150lb main
Moton Double CO

I know the springs rates are excessive since this how this is how I got the car when I purchased it. I'm trying to figure out how I can dial it in where the car is neutral as possible (I don't want push, especially on a C4 but nor do I want the tail wagging at me).

Stats:
2850lbs w/ half tank of fuel
AWD
245/285 tires