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

 

Resurrecting this oldie. Do this size tire really fit up front on a stock 17" cup wheel? I was thinking of changing sway bar settings and was searching for old topics on the subject when I found this posting. I'm getting track tires just for the POC short track series (Streets of Willow) for the rest of this year, next year we will see what happens?

I have nothing but understeer with 225 up front and 255 in back. I can't get the back to rotate for my life. Dump (let off) the gas mid turn and nothing, stops the pushing but doesn't bring the back out, ANY!!

Have (I think it was) -2.5 degree camber up front if that helps fit under the guards?

Thanks,
Dylan.

 

Dylan and Buck:

I have something unusual that you might be interested in. It is an OEM Porsche 993 Supercup rear sway bar that is 18mm in diameter and has three adjustment holes. It would require RS drop links, but those are readily available. Let me know if either of you are interested.

Hank

 

If you don't buy Hank's bar, you can mount up a 21mm 993TT Turbo (RoW) bar. There is enough room to drill another hole forward of the stock hole. Connect your stock drop links into that extra hole and you'll have a stiff rear bar, and you will have more fun at the Streets of Willow. I have a 22mm front bar, 21mm rear bar and seem to have beat the understeer blues at the Streets of Willow...last year. I am now at Big Willow...no problems there with understeer.

 

[quote]Originally posted by PeanutinCA:
<strong>I have nothing but understeer with 225 up front and 255 in back. I can't get the back to rotate for my life. Dump (let off) the gas mid turn and nothing, stops the pushing but doesn't bring the back out, ANY!!
</strong><hr></blockquote>

Hi Dylan,

Yep, I know the feeling. Some time ago, I was doing a pitch and catch exercise at a local driver training event. It seemed that no matter what I did, I couldn’t get the back to come around, and we were even on a wet track! I finally learned a very important lesson, though. If I lifted at high RPM’s (over 5,000), the compression braking would cause the rear to lose traction and come right around. If you’re lower in the rev band (say 3,000), you can lift all you want and nothing happens. I spoke with one of the instructors, one who has professional racing experience, and he confirmed this. You need to be high in the rev band to get a 993 to come around!

I call this an important lesson because it can help prevent an accidental lift-induced spin. It’s common to hear people ask, “what if I come into a corner too fast?” The typical advice is “whatever you do, don’t lift.” Well, if you’re low in the rev band, go ahead and lift (within reason, of course, and don’t sue me if you spin!). If you’re high in the rev band, don’t! If you have time before the corner, you can upshift to lower the rev’s before the corner.

Hope this helps!

Tom
’95 993

(I hope these comments don’t provoke any flames. Remember, I’m not a race car driver, I just play one on weekends! And I'm certainly not the best driver on this board! If you have something positive to add, please feel free.)

 

Strange things these 993's...

I can slide if I want with 225's & 255's. I could do that even with 205's in front.

I'm happy though, I like the way it handles, nice, controllable oversteer set up suits me!

 

Tom,
You are right. But you also have to be close to the handling limit to get the car to lift throttle oversteer. Even if you are at 5000+ rpm but only cornering at 7/10ths you probably won't get much rotation. I know that when I lift the throttle to rotate the car it is very brief and then I am back on it. Sometimes it is not a complete lift. I will get off the throttle a 1/4 and it will change the cars attitude just a bit.

If I turn in too early I stay on the throttle but maybe only 1/2 or 3/4 instead of all the way. A complete lift will upset the car but a smooth release of the throttle will probably get you through the corner if you overcook the entry or turn too early.

993's are very forgiving but you have to be smooth with the imputs.

Greg

 

Hi gents,
thanks for the inputs, pretty much things I'm doing/trying. What I'm talking about is pushing the car through a corner to the limit of front tire grip (and beyond), so revs might not be up in the 5K range (2nd gear). Can't change down to 1st so I need to look at it from an add grip to the front stand point. Now, most people adjust the rear sway bar to reduce oversteer. BUT, is this REMOVING grip from the rear? Can I change the front first to ADD grip up front, then if still pushing start to remove grip from the rear?

The other thing I couldn't find in the archives is which way to go on the holes to figure out what is harder or softer? Comments appreciated.

FWIW, Kuhmo Victoracers.

Cheers to the knowledge base.

Thanks,
Dylan.

 

Dylan,
You are on the right track. You want to fix the end that isn't working first.

Things you can do to reduce understeer:

Soften front sway bar. (holes are closer to the end)
Increase tire width.
Dial in more negative camber.

Then go to the back of the car and:

Stiffen sway bar (holes furthest from the end, closer to the inside)
Decrease tire width
Use less negative camber.

 

Thankyou Greg,
that's SPOT ON the answer I was looking for. I thought it a little strange that I need grip up front but I was being told to un-grip the rear to do so. Once I have done all the "up front" changes, then I will go to the rear and start to reduce.

What about Buck's original post, how wide can one go with say the Kuhmo tire on the stock cup wheel?

Cheers,
Dylan.

 

What is the stock cup wheel? 7.5" or 8.0 With the 7.5 you probably shouldn't go anymore than 225. With the 8" you could go to 245 but that is less than ideal. I run a 9"wheel on my car with a 245 tire.
With the right offset you could easily get a 255 or 265 tire up front but you would want a 9" wheel width.
Will the rear wheel fit on the front? Seriously I know a guy that did that with his 996. He runs the same tire and wheel all the way around.

Greg

 

[quote] ...What I'm talking about is pushing the car through a corner to the limit of front tire grip (and beyond)...<hr></blockquote>


Dylan,

If I may offer, just for perspective and certainly no criticism, that perhaps you're experiencing too much understeer due to how you are taking a given corner. I am no expert, but I know that I can easily induce understeer by "overdriving" the corner, coming in too fast, missing my turn-in point, etc. I, too, once complained of understeer as well, but that was easily remedied with swaybars...nothing esoteric, mind you, just M030 bars, conservative (to many here) camber settings, and 225/275 Kumhos. Bam! Neutral handling with the ability to rotate the rear end (within reason, as Greg stated very accurately). Perhaps I don't understand entirely your position since I only drive the track and have never done an autox...assume it's much tighter and requires more rotation. Or perhaps you're driving closer to 10/10ths than I am. Just my thoughts, in any event.

Edward

 

Hey Edward,
the understeer I'm experiencing is anywhere from the apex of the corner to the track out point. So, I'm thinking I've slowed enough and hit the apex? I'm talking about the the Streets of Willow. I have the RS swaybars (set to middle/middle I beleive) and whilst track temps were a little cooler in the morning last time out, started running straight into the 1.18's, 1:19's consistantly. They were used Kuhmos that I also drove to work everyday so I think there was some degradation there? Plus a Kuhmo (rep) told me to run low to mid 30's hot which I feel (and I found out since) is not the optimal temp. But all that said, I think I'm doing it mostly right but the faster I try to go now (from the above times) the more and more the understeer is coming on. Which is why I'm trying to dial it out. In the whole two days I only had the back out a little once on these tires versus being able to induce oversteer with the original (and I mean the on the car day 1) tires shortly after buying it.

Greg, I thought the stock cup wheels were 7" up front and 9" in the rear? <img src="graemlins/oops.gif" border="0" alt="[oops]" />

Maybe a tire place will play around with sizes for me?

Cheers,
Dylan.

 

Hi Peanut

Plus a Kuhmo (rep) told me to run low to mid 30's hot which I feel (and I found out since) is not the optimal temp.

So what temps does he like? I was running 37F-39R hot autoXing until last weekend where I tried 37F-37R better! and then 37F-35R even better 2 dealing w/ push in slow corners. I was thinking of going lower next time out!

 

Hey Cary,
I was running 40 front and rear hot, it runs really well (for me) at those pressures straight off the bat. Which MAY be close to your temps to start with if your not running lap after lap after lap autoXing and thus heating the tires up as much? Now, I could probably start altering by a couple pounds down to see the effects? But, it was suggested to run like 31-32 hot all round. This gave a noticeable amount of squirm and movement in the cars characteristics and my laps times slowed immediately. Heat was to blame for slower times at the end of the day but in the cooler morning, my times dropped in my second session after dropping the pressures.

So, do you lower the rear pressures to reduce understeer?

Cheers,
Dylan.