Nol, 95 993 C4

We have a track event coming up where we take our P-cars on a very tight and twisty Go-Kart track. The format is one car on track in a timed lap from standing start, one recce and two runs allowed. Last time around I was fighting understeer a lot. I'd like to improve on the car set-up and on how to attack the course.

There was a thread on understeer in the C4 a few days ago, proposing fat rubber up front. But I want to reduce understeer without actually changing wheels/tyres/suspension. I have ROW non M030, currently running 17" 996 twist wheels with Michelin Pilots 205/255. "Standard" specs for alignment and pressures 37psi F&R as per Porsche recommendations.

1) Change alignment settings. To what spec?
It is a daily driver and I'd like to keep it "mild" rather than "wild" and I do care about even wear.

2) Change tyre pressures. To what?
How about 35F 37R? No chance to put heat in tyres before the run, local ambient is 105F or so.

3) Run with full fuel tank? that was suggested to aid front end grip in another thread a while back. It feels counter-intuitive though, last time I made sure to have an almost empty tank.

4) Downshift to first in very tight hairpins?
I did this last time, some 3 times during the 55 second lap. I felt the engine was really at too low revs in second in these turns. But not enough time in the event to try out both and compare. What do the autoX guys do? How to decide?

5) Induce oversteer?
There's a couple right hand not so tight 180° turns with some track space. I enter them in second at good revs. Is there a way to "persuade" the C4 to power oversteer through these? Is it quicker?

6) How to attack double Apex turns?
There's a section where you come downhill into an almost 90° righthand turn followed by a second, much tighter 90° righthander that goes back up the hill. I attacked the first turn, setting up wide on the left and going across the inside to come out wide braking hard and then going for the inside of the second righthander. I ended up pushing really wide right in the middle of the second turn, not even on the exit I believe. I braked to not put wheels on the dirt and lost a lot of speed/time going uphill after that. What is the most likely error I made there?

Appreciate any tips and feedback, I have until end October to prepare.

Enjoy <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Nol

Stuart Ross UK 1996 C4

I too have been experimenting with tyre pressures to reduce understeer on a totally stock setup.

I have to admit to not having too much success as yet, and always seem to return to my original settings of 36 PSI all round.

The best policy seems to be to follow the fundimental rule of "Slow in, fast out", and really plant it at the apex in attempt to promote a bit more oversteer.

Alternativley pray for rain, thats when I find my C4 is at is best !!

I would be interested to hear how you get on, especially with respect to tyre pressures and results.

Kindest Regards

Stuart

Martin S.

My observations...note I do not have a Carrera 4, just a Carrera 2.

Downshifting to 1st...this is not for me...this has got to be hard on the transmision and clutch.

Oversteer: Install a 21mm rear sway bar. It has enough room on the ends of the bar where the drop links go in, to drill a second hole. At a tight track connect to the hole that makes the bar the shortest, most stiff.

Or find a really soft bar to the front in conjunction with the super stiff rear bar.

Good luck with the event.

Steve Lavigne

You could try disconnecting the front sway bar altogether.

Jim Michaels

Atta-boy, Steve.

Nol, 95 993 C4

Thanks for the feedback so far, already the anticipation is proving fun. I have had some time to think it over since posting and here's the current plan:

- Keep it in second gear and see where that takes me compared to last time out. Martin confirms my gut feel, but the revs do get low
- 35F 37R tyre pressures,
- Get a full alignment done and go a little more aggressive e.g. on the front negative camber

However, I think maybe I should not just dial in more negative camber up front, but rather adopt a complete set-up to get the car to handle better. Would RS settings be a reasonable compromise fr the street too, or rather too aggressive? A benefit is that with RS specs I can simply refer the local mechanics to the factory guidelines.

I'm not quite "ready" yet to disconnect swaybars and the jury is still out on the fuel issue.

This is a fun, gentlemen drivers afternoon out and far from a full DE or track day. But last time out the ol' adrenaline pump didn't seem to get that signal from the brain and there are some nice prizes for the fastest times.

Enjoy <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Nol

Glen

The very best thing you can do is to put 225's up front...single best handling improvement for a C4...

cfdarch

Hi Nol

I've been running autoX w/ local SCCA chapter. One of the places we run is on a oval trak plus a mini road course that feeds off/on the back of the oval. Most of the run setups are in the 50-60 second range. I have Gerts RoW M030 w/ Bilstein HD. Maybe I should have keep the front stock sway bar and just stiffened the back! I have recently started running more air pressure in the front than the back (37F / 35R hot) on R compound Kumho's. It helps. I will probably try increasing the differential to 3-4 lbs next time out. I rarely downshift to 1st though I am frequently tempted. I will soon have the car corner balanced and aligned at the extremes of the specs as the car is an almost everyday driver. Have been running the tank half-full (worst of both worlds??) basically so I can get to and from the track w/o stopping for fuel. Check out the link below.

<a href="http://www.tirerack.com/tires/tiretech/competition/racepres.htm" target="_blank">tire rack over/under steer</a>

JohnM

Hi Nol,

Re RS settings and suitability for street use, my C4 is on RS alignments at RS ride heights running PSS9 and RS bars, it's great as a daily driver, do about 20k miles per year in it.

Nol, 95 993 C4

Glen, I have a set of 996 wheels, a half inch less rim compared to 993 cups. I'm afraid the 225's are one number too much on my 7" rims.

I am confused with the tire rack info. I thought lowering front pressures within reason would increase grip, hence reduce understeer And quite a few threads, arguably for 18" wheels, refer to staggered pressures with the front lower by 2 psi. What am I missing there? Do increased pessures prevent the tyre from squirming and "rolling" or some other dynamic aspect?

JohnM, thanks for the thumbs up <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" /> , does the RS spec reduce understeer? I only just realised that it is conceived for RWD rather than AWD, but should I care?

Enjoy <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

joey bagadonuts

Trail brake. In the 964 C4, applying the brakes in a turn will get the tail out--it basically frees the wheels. Normally, it's a locked differential which promotes serious push. Not sure how it affects the 993, though.

I just spent a weekend at a track which featured a hairpin turn. The trail braking allowed me to spin around it like a rally car.

JohnM

Hi Nol,

I haven't run the car on a tight track so can't comment on that situation, but on an average track (whatever that might be ) including a hairpin I haven't had problems with understeer, but plenty of problems with slower cars in the way (Ferrari drivers, eh, what can you do ). The extra negative camber on the front (-1 degree with RS settings) definitely gives the front end more bite on corners with fast entry - or so it seemed to me. I have 17" wheels with 205 fronts/255 rears, front bar 1 off full stiff and rear bar in the middle so to read some of these posts you'd wonder how I even get the car to turn into my drive but fact is it works very well, at least for me.

DJ

Joey Bagadonuts has got the right idea: the biggest factor in getting around the course quickly will be "how you drive it". Diving in deep, hard on the brakes as you turn in, rotating the car with the brakes, and then smoothly transitioning to power oversteer will get the job done. Also, quickly snapping off the brakes and then throwing the car into the corner while it's unsettled will do it too. If you still can't get the car loose enough, put a bunch more pressure in the rear tires. You're going to need to steer the car as much with the throttle and the brakes as you do the steering wheel.

It ain't easy, but it sure is fun.

Martin S.

[quote]Originally posted by Steve Lavigne:
<strong>You could try disconnecting the front sway bar altogether.</strong><hr></blockquote>

You have got to be kidding. What incredibly lame advice. We are trying to help this guy, not get him killed or injured. You WERE joking, correct?

Robert Henriksen

I've also got my alignment set to RS specs, and my street tires (which only see street driving) don't have any uneven wear -- yet, anyway!

Surprised no one else has suggested a strut brace. I found turn-in much improved when I put one on.