kgorman

I was at Sears Point last week and finally felt like the suspension setup was starting to get pretty good. Here is a summary.

My car is mainly a DE type car, but with some weekend play as well. Immediately after purchasing my 964 C4 6 months ago, I promptly took it to Sears Point for a shakedown in stock form. At that time the suspension was awful. The shocks were worn out, there was drastic body roll, and the car understeered very badly. It was still fun though.

For instance, turn 7/7a required quite a bit of throttle lift to get the car to turn. Turn 5 felt very unnatural, and turn 11 the car would understeer and 'skip' the front end around the corner.

Immediately after that event I started in on changing out the suspension. Last week the suspension felt much better. I still have a couple of changes to make, but I am almost there. Turn 7/7a I can now take w/o lifting to rotate the car. I do trail brake a bit leading into it. The car gets into a nice drift and turns nicely. Turn 8 feels oh-so planted. Turn 5 feels good now, I have good confidence adding progressing power through the apex. I do get a bit of bottoming out/rubbing though. I can also get the car turned, and start with the throttle earlier now in 11. I turned a 2:09 last time, I don't know how good that is really, but it felt like a good lap. I have a lot to learn, but I am getting better.

Here is a good read about the C4:
"Wringing out the C4" here: http://www.porsche964.co.uk/rev_rep/excellence.htm.

Also I got Adrians book before I did anything (ISBN: 0837602939)

Here is a summary of my changes:

- Wheels/Tires
I switched out my d90's to genuine 17" 7"/9" ET55 Cup II (design 93) wheels. I have these riding with 3mm spaces front and rear currently. These wheels are a bit wider F/R (1") than the d90's and not too expensive. I have a new set of MPSC's (255/40R17 R - 205/45R17 F). I got them heat cycled from http://www.tirerack.com. These make a fantastic difference when paired with my other upgrades. I do get some rubbing on the oil line and swingarm under load (turn 5, or the carousel at LS..see avitar). I will be adding 56mm studs, and a 6.5mm spacer before the next DE effectively changing my offset to 48.5mm (55mm-6.5mm=48.5mm). I will also hammer my oil line a bit to add some more clearance. I already swapped my alum. lug nuts for open-end steel ones from http://www.performanceproducts.com. There has been talk on this forum of going 225/45R17 on the front to decrease understeer, but the MPSC's are already running a bit wide it seems. Perhaps the next set. I have not upgraded the steering stop from the 6mm unit to the 10mm, but perhaps I will soon just to be correct.

- Tire pressure
I start out with 28psi cold all the way around, and they warm up to 34R and 33F hot. I then let out 1 psi in the front and that helped understeer as well w/o the rear being to tail-happy. I target 34/35 hot R and 33/34 hot F, this combo seemed to be nice and I do get wear down the side, but not so much that they are rolling over. Wear appears nice and even so far, I expect long tire life.

- Dampers/Springs
I am using Bilstien HD/H&R dampers/springs from http://www.rennsportsystems.com/. I didn't go Moton/JRZ/PSS9/etc mainly because of budget. I do have some regrets as now I need a higher spring rate. Garrett recomends http://www.hypercoil.com. The H&R's are just too soft. These units are non-adjustable BTW. This is fine because frankly, ride comfort is not a huge issue, I just want it to be correct for the track, and I will deal with it all other times. I might need to get my Bilstiens re-valved, we will see. Also of note is since my car is an '89 I have a different rear shock setup than 91-94's. This is important when ordering to proper dampers. I am not using monoballs/camber plates. Just the stock bushing bits.

- Alignment
I got a good corner balance and alignment at http://www.kahlers.com. They put my car to euro RS specs for ride height, camber, etc. I just took Adrians book to them, and they used the info on page 262. This is the single most important part of the setup for both handling and tire wear.

- Sways and strut brace
I also got genuine RS sways and a strut brace from Steve at http://www.rennsportsystems.com. The strut brace seemed to really help turn in, and overall feeling. I installed the sway bar, and set the position to the middle position at first. I didn't notice too much of a change in that setting.. Last week was the first week that I ran on the hardest setting (hole near the bar itself, or 'inside' position), and WOW what a change. This is a must have mod. I have not put in the front sway yet, there is some question if it fits, and also some question as to if I actually need it. A couple more DE's and I will make a decision.

Thanks RL for all the info, this place is a god-send for reference.

Off to Thunderhill in a week to shake her down some more.

garrett376

The strange difference between a C4 vs. a C2 is that you can hammer the throttle through the corner and let the PDAS keep you in-line. It took me a while to figure that out, since you'd think you'd break away the rear end which would unsettle the car - but actually if you just plain floor the accelerator, it will whip through the turns! That's where the C4 PDAS 4x4 system is such a treat!!! Try it next time

agentpennypacker

The turbo/rsa H/R springs for the 964 are stiffer than the standard H/R. Christer posted the actual spring rate ranges not long ago...

Tom W

I use a big lift at both 7 and 11 to rotate the car (I use a double apex at 11). It makes it all that much more fun! While I love the turn 6 (the carousel), I find that i just love turn 5 - floor it at the exit of 4 and hang on as the G's build prior to braking for 6.

How did you feel your suspension felt compared to the ride in the Turtle (with JICs)?

FamilyCar

Hey dude, sorry I didn't chat more at SP. I don't recall the RS alignment specs, but I do recall the Sport Cups wanting more neg than RS specs: "1.5 to 3 degrees negative (for most basically-stock or moderately-modified cars, the "sweet spot" is going to be in this range)" according to Tirerack, numbers I've seen posted elsewheres too. Most folks that run the sport cups seem to need more negative camber than the ROW RS specs.

I run -1.6 front and -1.8 rear w/ 0 toe, which may not be enough either.

I have the 225/45/17 up front paired w/ the 255s in back. I have no issues w/ rubbing. I have a set of 205s w/ 8 heat cycles if you want them. Honestly, I think you may end up preferring the 225s though.

I have PSS9s. I guess I'm not entirely happy w/ them now. Don't get me wrong, I think the're a competent setup. I'm at 1 front 3 back. I get no high speed instability. They handle the little depression in T8 at TH just fine, actually superbly IMO. But I find the progressive springing just a tad disconcerting on the track. ..ooh I'm soft..oh, now I'm hard. (please I do not pun) When I bought the PSS9s the JICs I believe were about $400 more, really not that much more. Had I to do it over I might have listened to Turtleman, and gotten those, the JICs. I think Motons are overkill for most of us; just too much to fiddle with, unless you have someone do it for you.

People have been telling me to go to Matt Lawrence in Reno to help me set up my car. He may be a resource. He knows the NorCal tracks well. Others probably know more about him.

Have fun at TH.

Pat

kgorman

I am pretty sure most of my rubbing is due to low ride height + too soft spring rate. I think just a bit of spacer will help until I get new springs. Just got off the phone with Performance, they (and new 52mm studs) are on the way.

The RS specs are -1d F -1d15" R. Thats what I have. So far so good with the MPSC's, all was well.

Garrett, I will start playing with what you say. I am already starting to go down that road. It's fun. I get a lot of my little green PDAS light. I was wondering, at that point is my rear axle solid? Seems too brief for that to be the case.

Tom. I suspect as I speed up I will start to require a lift again as well. Now I am too slow to need it I am pretty sure. ;-?. I didn't get to ride in the Turtle, she is a beaut. Next time hopefully.

Family. Yeah, we need to hook up more. You are getting fast my friend. Love the new wheels! What about going down to Jerry Woods for car setup?

FamilyCar

Jerry Woods for car setup? I don't know, haven't heard/read anything pro/con. Tom might have an opinion.

FamilyCar

I want to ride w/ Tom too. You should ride w/ me and I should ride w/ you. Our cars are closer. Also I want to see how much of a difference there is under dry conditions.

kgorman

Yeah. Let's do it. When are you out next? I will go.

yugger

Kgorman,
Where did you pick up your Cup II wheels? I've been looking for some of those or Turbo wheels without much luck.

kgorman

I saw them on RL classifieds. Also try PCA Pano magazine or PCA classifieds.

FamilyCar

KG, PM sent, Tx

kgorman

I remembered this old post..

I have been trying this. Actually it's funny. I had an instructor ride with me. A Porsche 'guru'. They said I was actually getting on the gas too early. I beg to differ and so do my lap times. I think he was not used to a C4 and was coaching me more on C2 techniques. I also noticed that I can brake _way_ deeper, trail/rotate a bit, and then get on the gas. It's just such good fun, and fast I suspect based on my lap times dropping.

Thx for the tip Garrett.