I lifted the attached post from the 993 board, entitled "993 Understeer Cure":

"I autocross a lot (ASP) and have been fighting understeer for two years now trying everything from exagerated tire pressure staggers to swaybar adjustments. Well, I may have found the combination I've been looking for. A friend, an ex-national Solo II champion, kept saying you need more rubber on the front and had been trying to get me to put 255/40/17's on all four corners. I didn't think they would fit up front (lowered a little) but they do! I've had to work on the right pressure/swaybar combination (did a 180 snap spin my first run out with this set-up, but I had a big smile on my face). After two events (one conventional autocross course and a road course autocross (Carolina Motorsports Park)) I'd started to get it dialed in. This weekend we had the 20th Annual 24Hr DuMall (24 hour autocross) and I got about 25-30 runs to work on the set-up. Just what the doctor ordered. I ended up in 2nd place overall out of 183 cars less than .2 seconds off FTD. BTW, FTD was a D Mod 1700 LB Civic with more rubber on the ground than than I have.
Bottom line. If you've been fighting understeer you may want to give more rubber up front a try. It works!

Buck"

I'm new to autocrossing and realize my understeer problem is probably due more to my use of rapid acceleration through tight corners than anything else. However, I use 205 and 255 width tires front and rear and understand that I might be able to get more grip by using wider fronts. I just never heard of someone going to such an extreme.

I was wondering if anyone had used a similar setup on a 964 or would care to comment? Also, it seems such changes might adversely affect handling for DE events, i.e. excessive oversteer. Is this accurate?

 

I don't think you could get a 245 on the stock 7" 964 wheel, but I currently run 225's up front, and 245's on the back on the stock 16" Design 90 wheels. We are taking Kumho DOT tace tires here, not streets. They look a bit bulbous in front, but they seem to work.

The car is toally stock. The front suspension is as low as it goes (about 26 1/2 from the ground), the rear is set to about 25" from pavement to fender lip. I will doing shocks and springs for next season.

I have been playing with tire pressures a bit (I have autocrossed other cars for over 12 years, but am new to the 964), and took some advise from a contract Kumho driver I know through SCCA (he was my instructor at an autocross school).

He said that you want as much pressure in the rears as needed to keep the rears from rolling over too much, and as little as needed in the front so they DO roll over. Note, by roll over, I mean down to the arrows at the shoulder, but no further.

I have a total of 5 events on the car, and only at the last event did I finally get to the point where the car was really loose (aka wanted to oversteer). There was section of teh course called the carousel, in which one lap I drove in a Duke's of Hazard style. Not fast, be very entertaining. I then looped it in a fast sweeper. OK, I now know what it takes to loop a 964.

At my next event, I am going to drop the rears a bit, and raise the fronts a bit and see where I am at.

That may seem counter intuitive, but once a tire's pressure is within a reasonable range for the weight of that end the car, additional adjustments alter the tires spring rate, so a higher rate in front and a lower weight in the rear can help an oversteer situation. The stop watch will tell the tale.

FTR, a slightly loose car will be a faster in an Autocross than a car that will push....that is, assuming you can use the loosness to your advantage and not loop it. For road couse/DE, you would probably want the opposite.

Another thing to consider is that in features like slaloms, you absoluetely can not be abrupt with the throttle. Obviously, the weight will come off of the front, and she will push like a pig.

You may also consider playing around with leaving some wieght up front (I do NOT reccomend running with a near empty tank).

Good Luck and Enjoy.

BL

 

One of the top Boxster drivers in the local SCCA autocrosses runs 255's all the way around, including 255's on 7 inch wide rims. It's outside the manufacturer's specs, but he does it with great success. FYI, he runs on Kuhmo Victoracers.

I run 205/255's on R compound tires and have massive understeer. I'm going to run 225's on the front soon and have it corner balanced and aligned. My front tires are wearing along the outside edges, so I think a camber adjustment will help.

That's another idea: check your alignment. You'll have more understeer if you only have half the tire touching the ground during turns.

 

Drew,

With a stock suspension, you will likely always wear the outside edge of your tires faster than the inside (at least that has been my experience). You do want to watch the pressures to avoid excessive roll over.

In fact, many of my SCCA buds actually will flip the tire on the rim when the outside is worn down. You would not want to do that at a National event, but for local/regional stuff, its fine.

The inner edge will normally NEVER get used up on a typical stock suspension in an autocross situation (even a Porsche).
That said, negative camber is a good thing. The best I can get now is about -1 degree. Lowering will help that a lot.

As far as massive understeer vs. oversteer, I felt the same way up until the last couple events. I find that our local SCCA region runs things very tight, and the car will push badly on those courses (I won't be doing many more of those events!). The PCA guys, however, keep things much more open, thus the car feels much more neutral.

Two events ago (the event pictured), I had oversteer on corner entry, right after I got off the brake, then mild understeer from mid corner through corner exit . You do want to be smooth when transitioning from braking to corner entry!

At the last event, I had oversteer on corner entry, well into mid corner. As I get more comfortable with the car, I am pushing harder and finding the limits (mine and the car's. At the moment, mine are lower!).

As a driver, I really need to recalibrate my driving style adjust to the 911 (my last car was a Integra Type R).

Without giving too much away, I would say that front to rear presuures (in my case) are quite a bit different (look at the data plate inside the drivers door. Porsche engineers are NOT idiots!), and as I said to Joey, you don't want to lighten the front of the car.....it is already too light as it is.

Of course, with a lowered suspension and stiffer spings and shocks, the game changes, and everything that I think I know thus far probably does will not apply!

Regards,

BL

Lastly, a photo of the car on track.

 

Thanks Brian and Drew. As I suspected, there are a number of variables to consider when trying to get through the cones with decent times, not the least of which would be my driving technique. FWIW, I've noticed that the C4's AWD will pull the nose through a corner quickly once traction is regained (just like a FWD car), so there's yet another wrinkle for me to keep in mind as I strive to smooth out those corners.

So how's the 964 holding up for you, Brian? I recall from another post that you had reasonable success at the National SCCA level with another vehicle prior to switching to Porsche. Has the extra torque made up for the loss of agility?

 

Joey,

Lets just say that I learn something new every time I take to the track! But yes, the torque (compared to my Integra Type R) is a wonderful thing.

Even better is how the car feels at sea level. I live at 5500 feet, which is a major performance drain. I went to San Diego in the spring and felt like I had twice the power (probably more like a 30% boost, but you get the idea!).

I will not be threatening for any SCCA National trophies for a while, but thus far, I am having a blast with the car. At the end of the day, its all just driving. Whether a car is FWD, RWD, AWD matters little. You need to learn the traits of the car, and just drive it.

At our last PCA event (the Fiesta del Porsche autocross), I took second in class to a Boxter S. FWIW, in SCCA stock class (BS for the 964), the Boxter S is two classes higher than the 964 (in Super Stock). In fact, the normal Boxter is in the same class as the 964, and there is talk that it may get moved UP next season! So, I don't feel too bad about 2nd place.

I have been asked to join my region's PCA rules committee. That will be a good time to talk about the Boxter S

Regards,

BL

 

Brian,

Yes, there's no question that "it's all just driving." Sure, the FTD driver at our last autocross had slicks and an "improved" setup, but he also drove with amazing precision. I might've improved my time in his car, but I would have never come close to his best time--not yet, at least.

Here's how we brake out the classes at <a href="http://www.pca-chicago.org/autocross/2002rules.htm" target="_blank">PCA Chicago</a>. I'm not aware of the rationale, but it's interesting to see that the Boxter S is one group below the 964 and the Boxter is THREE groups down in a class with 951's and 968's. I haven't seen complete times, so I'm not sure if there's a correlation. As for being grouped with 993's, that doesn't seem to be a problem for the 964. Taking the class was a C2 followed closely by an RSA. The 993's took third and fourth and then it was my C4 (woo hoo!).

Thanks for sharing and good luck.

 

Brian, I should have said "excessive" wear on the outside edges. I recently brought my street wheels (I have separate track wheels) to a Porsche suspension shop to have the tires replaced and the owner said my camber was too positive in front, based on the tire wear. After he pointed it out, the uneven wear did seem strange for street tires that I never drive hard on, such as for autocrossing. The outside edges were extremely worn out compared to the inside edges. Either way, my car could use an alignment since it hasn't had one in years.

I also flip my R compound track tires when the outside edges wear out. Great way to extend the life, and it's also why I won't buy asymetrical, directional track tires.

Brian- you also have an Integra Type R? I just bought a second generation Integra RS that I autocrossed in this past weekend for the first time. Very fun car although certainly not as capable as my C2 (*duh*). I was surprised that I could step the tail out. It was actually more sensitive to trail braking and trailing throttle oversteer than the C2, probably because the suspension is a lot softer. Very fun to drive, although I will seldom autocross it.

Joey, your local PCA ranks the Boxster S below the 964? That's pretty surprising. Our local PCA also has, IMO, pretty inconsistent class designations, but it's just for fun so I don't really care. I just joined the autocross committee so perhaps I'll get some insight at our next meeting. I tend to trust the SCCA stock class designations, which seem to be pretty accurate.

Drew
92 C2

 

I don't autocross, but I do get on the track a fair amount. My setup is pretty neutral, perhaps a little easier for a C2. For track tires I use 225x17's in front, 275x17's in back (Kumho Ecsta 700's R compound), and -2.5 degrees camber front and -2 degrees rear. I have a Carrera RS suspension with adjustable 24mm swaybar up front and 21mm adjustable in the rear, and it's lowered. I'm told you can put up to 245's in front on our 964's, although it's tight, and you can go larger in the rear, although you may have to grind off or roll the fender lip.

 

I've run an RSA in ASP for over four years. To reduce understeer (actually achieve desirable oversteer) for autox, I simply disconnected the swaybar on one side by removing the downlink. Afterward I had to alter my throttle application habits in tight turns, because the first time out I entertained spectators by steering like crazy every which way (too much throttle). I was then convinced that part of my initial understeering problem was simply using too much throttle in tight turns. Like many others, I was pushing it (the throttle that is) too hard in tight turns. Remember to reconnect the sway bar link before going on track, where oversteer inspires fear.

In short, a softer front end (relative to the rear) reduces push/increases oversteer.

 

[quote]Originally posted by Jim Michaels:
<strong>I was then convinced that part of my initial understeering problem was simply using too much throttle in tight turns. Like many others, I was pushing it (the throttle that is) too hard in tight turns. Remember to reconnect the sway bar link before going on track, where oversteer inspires fear.

In short, a softer front end (relative to the rear) reduces push/increases oversteer.</strong><hr></blockquote>

Jim has it 100% right....

In the 964 C2, you absolutely positively must control your throttle application in corners. She will plow like a cheap farm impliment if you try to apply power with the front wheels turned much beyond straight ahead.

I really have come to think that the real way to go fast in a C2 is to be patient and smooth with all the controls, and particularly with the throttle.

When in doubt, consult the friction circle.

And he is also correct that you MUST soften the front end to try to balance the handling.

Enjoy!

BL

 

Thanks again, all, for your good counsel. It's much appreciated.