RSAErick

For those who have experience with 964 track cars,

After my first half of a season of track days (DE and lapping days), I'm finding myself longing for a better car setup. My car is a stock RS America, except for Eibach springs. The car has a "performance street" alignment and is corner balanced. The result? A car that handles "relatively neutral", but in slow to moderate corners, understeers massively.

My questions are these:
What can be done about the understeer in these cars, that isn't going to cost me an arm and a leg?

Are the Eibach spring rates sufficient for the track? What spring rates are considered ideal for these cars?

Are the stock MO30 shocks sufficient for the track? Can they be revalved or replaced with something better?

Is the stock front sway bar sufficient for the track? Would a bigger bar help? Adjustable bar?

Would R-compound tires solve my understeer problems?

Thanks for passing along your knowledge!
Erick

cbottone

Eric,

I run a 964 C4, so my experience is tied to that. They understeer even more than the C2 in general.

Springs and shocks should be matched to get the optimum performance. Aftermarket springs that lower the car are sufficient for performance capabilites required for street driving, but for the track i would go with shocks recommended to work with the Eiback springs. I believe Koni makes a shock that works with these springs. I use H&R/Bilstein setup w/ adjustable stiffer rear anti-swaybar.

A stiffer rear anti-sway bar of the adjustable type can also help reduce understeer. you should'nt need a stiffer front anti-sway bar if you're experiencing understeer.

8" (width) wheels with 225 or 235 width tires in front help reduce understeer and increase turn-in responsiveness. Are you running on 6 or 7" 205's?

Stickier r-compound tires will help a lot against understeer. This may be the cheapest thing to try first, but there is a downside.

I firmly believe the downside of switching to r-compound tires is that they will handicap your driving learning process. They allow you to be less smooth in your weight transitions and you don't need to learn the same level of sensitivity of the traction dynamics of your car at speed. You will turn faster lap times, but its a false accomplishment. You will not learn how to be a quick driver as soon as if you stay with less grippy street tires.

A final word regarding springs and shocks. I've run with stock 964 RSA's at the same track and we have looked at video of our cars through several turns. The stock RSA (M030 suspension) sits taller, is more softly sprung and rolls more in tuns on the track. The aftermarket spring/shock kits from Eiback/Koni and H&R/Bilstein lowers and stiffens these cars more than the M030 sport option. I think the aftermarket setups are more suitable to the track, if you are comfortable with a slightly stiffer ride and lower clearance.

chet

JC in NY

What's your budget for suspension improvement?

RSAErick

Thanks for the very useful response, Chet!

To answer both yours and JC's questions:
1. I believe that my wheel dimension are 7x17" in the front and 9x17" in the rear. They are the "cup 1" style - not the same as on the 993's.

2. My budget is a difficult thing for me to determine. I would rather do the upgrades incrementally so that I can afford better quality equipment. At the same time, I am not interested in spending the astronomical amounts of money that companies like JRZ and Moton want for their suspension setups - I just can't afford it, and I'm not getting paid to race.

I hope that helps. Thanks!
Erick

JC in NY

OK, fair enough.

You should consider a set of H&R coilover with RS adjustable antiroll bars. You can get this setup for under $2000 for the parts from <a href="http://www.carnewal.com." target="_blank">http://www.carnewal.com.</a> This suspension will give you a good dual purpose street/track suspension which is tunable. Another similar alternative would be the Porsche original European 964RS suspension.

Tim Comeau

Erick, Your problem is not uncommon. 964's understeer like pigs. THE RSA is a slightly modified 964. It's one of those projects that the factory did half-assed. It should have come with bigger wheels, tires, brakes, and more horsepower. Oh,well.... I drive/race an RSA. Here's my advice: Get bigger wheels. Go to 245's in front and 275's in the rear. 205's up front are a joke! Get some Carrera Cup adjustable sway bars, that's the key! Once you get some decent grip up front you can dial the balance in nicely with these adjustable bars. Our car also has H&R's and adjustable Koni's. But get some bigger rubber up front and get the adjustable bars front and rear and you'll be good as gold. Promise. TC

RSAErick

Fabulous! Thanks guys!

But now I've got some more questions, pertaining to your responses...

First of all, are "coil-overs" the same as a spring outside of the shock setup... meaning, would H&R springs with Koni shocks be considered "coil-overs"?

Second (and this one has been troublesome for me)... which sized newer 17-inch Porsche wheels can I pick up used that will allow me to put 245's up front and 275's in the rear while maintaining the 55mm offset??? Is my only option to go with aftermarket wheels? I didn't think that Porsche made 55mm offset wheels after the 17-inch "Cup 1" wheels that came with the RSA!?!?

Thanks.
Erick

Bill Gregory

As you look at options, you may want to consider a non-Porsche rear adjustable sway bar. The Porsche Carrera RS rear bar is an 18mm bar. I installed a Weltmeister 21mm adjustable bar, to help tame the understeer. TRG also has adjustable bars larger than the Porsche 18mm.

Note that with 275's in the rear, wheel offset is important, and you may need spacers to get it right. You may need to further flatten the "flat" oil line on the right side, as well as flattening sheet metal in a small area at the inside rear of the wheel well against the body to ensure tire clearance.

Craig W.

I've run fairly well developed a '91 C2 on the track for the past 3 years (same as a RSA, but smaller brakes). I used H&R Supercup coilovers with AJ USA adjustable sway bars. I believe this is a very similar setup to what JC in NY recommended. So that is a good place to start. It seemed to perform pretty well, especially considering the price/perfomance ratio compared to JRZ etc.

To save money, you can use the stock sway bar in the front, and just get an adjustable rear bar. Set the rear bar full soft, then move it to harder settings to dial out understeer. A wider front sway bar, though adjustable, may make the car understeer more.

Before you do that though, you need to address the wheel/tire width that Tim Comeau mentioned. The stock 7's on teh front are simply too narrow. After trying many combinations, what worked best for me was 8's and 9.5's, with 245 and 275 or 285 rubber. If I recall correctly, 285's DID tend to rub on the oil line, so I used 275's for the most part.

To get the best bang for the buck, I would make the upgrades in this order (since you mentioned incremental upgrades):
1. Wheels and tires
2. Adjustable rear sway bar
3. Coil overs w/ adjustable camber plates
4. Adjustable front sway bar if needed

JC in NY

[quote]<strong>After trying many combinations, what worked best for me was 8's and 9.5's, with 245 and 275 or 285 rubber.
</strong><hr></blockquote>

These are the wheel widths used on the Carrera Cup race cars in Europe for both 17" and 18". I don't agree with your tires sizes though. I think 225/255 or 225/265 is a better combination for these widths.

Craig W.

Regarding spring rates:

The H&R Supercup kit I used came with springs that were about 400 lbs front and 600 rear, I think. They were just right for learning the car, and learning to drive.

As I got faster though, in high speed and/or high G force corners with R compounds, I would actually bottom out the suspension under load. This effectively increases the spring rate to an infinate number, and causes nasty things to happen. Most important is a tendency to very suddenly lose traction and spin, with no warning. Well, maybe 1/4 a second of warning.

Heavier springs solve this problem. If you go too high, you will need to revalve the shocks as they will be overpowered by the heavy springs, causing wheels to "pogo" under load. Too high is also bad on a bumpy track, as the entire car will hop sideways over rough pavement, forcing you to slow down. It's a delicate balance, and professional race teams often have different sets of springs for each track, and even for different driving conditions (hot/cold/wet etc).

How heavy to go to is a function of your driving skill level, driving style, smooth/bumpiness of the tracks you run, speed and tightness of the corners on the track, etc.

The last set of springs I had on my car were very heavy, well in excess of 1000 lbs in the rear.

RSAErick

[quote]Originally posted by JC in NY:
<strong>

These are the wheel widths used on the Carrera Cup race cars in Europe for both 17" and 18". I don't agree with your tires sizes though. I think 225/255 or 225/265 is a better combination for these widths.</strong><hr></blockquote>

If you are right, then you guys have got me a little confused here...

If the 8" x 17" front/9.5" x 17" rear combination is the best "wheel" combination, then great.

If it is the 245F/285R combination is ideal, then I need to find the wheels that support that size of tire.

Which ones should I go for, if they aren't the same thing?

And how do you know which tire widths fit appropriately on which wheel widths? Is there are guide?

Thanks so much for your patient help! I really want to get this right.

Erick

Alan Herod

For experimental purposes (and low cost approach), what about a little less toe-in on front? Try a few different toe settings, till you get it to what you like.

Craig W.

Erick,

JC in NY and I (I think, hehe) that 8's and 9.5's are pretty good.

But another issue is what size tire to put on those wheels. The larger the number, the larger the tire.

A bigger tire puts more rubber on the road (for the most part, but let's keep it simple for now), but also can squirm more, making the handling less than optimal at the limit of traction. A smaller tire puts less rubber on the road, but spreads that rubber more tightly over the wheel, reducing squirm, and increasing turn in, crispness, and stability at the limit.

As you increase the size of the tire mounted on a wheel, eventually the increased squirm outweights the increase in traction and starts to actually become a negative rather than a positive.

I never was able to feel the squirm with 245's and 275's. So I felt good about getting more rubber on the road.

Others disagree, and justifiably believe a 225 on the front and a 255 or 265 rear combination is better. I have no reason to disagree with them.

I suspect that "After my first half of a season of track days (DE and lapping days).." it is pretty unlikely that you are at a point where you could tell the difference yet. I could not really tell after 3 seasons of running a full POC schedule. But then again, I did not actively compare the two set ups.

So what to do? Just get whatever will fit the car and not rub, then go drive and have fun. When you are driving at the 99th percentile in every corner and every session/race, then maybe it's worth the time to see which works best for you and find that extra 10th or two per lap....

JC in NY

I agree with what Craig just said 100%. There are trade-offs to using either tire combination on the same rims. Ultimately the correct choice is what gives you the best laptimes. My guess is that they will be very close (within tenths) and the tie breaker will be your setup and driving style.