[wiseman]

Ran my first Autocross Sat with the new M030 bars on. Rear in the middle slot. Didn't have the Yellow Sports on the rear........ran out of time and they needed a week with WD40. Anyway, I was running 2354017 Nitto NT05's on the front and 2554017 05's on the rear. Started at 40 PSI. First run the nose went right where I pointed it but the rear came around really fast. Kept an eye on the tire pressures and kept dialing them down 2 lbs a run with the rears always 2 lbs below the fronts. It got a little better and the times got down to within a second of the perrenial class winner who runs a 944S2 with Khumo Victoracer R-1's, but still fought the oversteer all day.
Next Autocross is this Sunday. I know the rear shocks will help and I'll get them on this week. From what I've researched here, I'm going to move the rear bar to the outermost (softest) level. Does that sound right to eliminate oversteer and promote a little understeer? I think I may have to invest in the lower strut brace also to tie the car together as the Design One upper brace doesn't quite work with a 92 model.............the towers are about 3/4 of an inch closeer than other models.
Any advice guys?

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[flash]

tire pressures are WAY too high - i think you'll end up about 30 cold

i wouldn't change the rear bar setting just yet - a bit of oversteer is a good thing - on autocross cars, we actually disconnected the FRONT bar to help induce a bit of oversteer

lower brace will help a lot though

doh - i still need to make an adjuster for the early 92s - my bad - i'll get on that

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[Tom030]

Flash is probably right on the tire pressure being too high. You might try mid 30's with about 2/3 pounds less in the front to induce some understeer. After years of fighting snap oversteer I set the rear bar at full soft and set the air pressure at 32 to 34 all around depending on weather conditions. The "snap" oversteer went away allowing me to brake later and harder. Steering response is slightly slower but stability under braking is greatly improved and well worth the change.

~tom

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[wiseman]

I checked the tires when I got home and at those pressures, I'm scrubbing the outside corners down about a 1/4 inch into the shoulder..................theirs no wear or scuffing on the inside half of any of the 4 tires. All on the Outside shoulder and outside half of the tread.
Flash-----when I'm talking oversteer..............I'm talking Drifting kinda oversteer. More than I've ever experienced. My alignment is 1 degree Camber in on the fronts and right at 0 at the rear.

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[flash]

interesting - having driven a momentum car forever, and quite a bit in autocross, i don't do a lot of braking, and instead throttle steer to get aorund the course - this means that understeer is a very bad thing, and need to set it up with a touch of power oversteer - understeer scrubs off speed, and upsets weight transfer - oversteer is manageable, but you do need to learn how to use it - it means that you might not be going into a corner as fast as you might, but it does mean that you come out as fast as you can - it's a lot about rhythm and you need to practice a lot, but it does result in lower times once you get good at it

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[wiseman]

Yup your right..........Danny Sheilds runs the Suncoast PCA autocross events and is at every Autocross we have. He is always available to help. He wins about every Boxter Autocross at the Porsche Nationals and is a 5 time SCCA campion. He drives a stock Boxter S and just flies around the course...............My class winner with R-1's was a 31.1..... I'm running 32.1 ..............he runs a 28.4. I guess if it was that easy............we'd all be champions. I definately have some work to do.........I just want to be sure I'm giving myself a fair chance.

I found a few 9" Boxter wheels on Ebay which will allow me to run 255's up front and rear. I'll get the shocks on and dial down the pressure next weekend. I'll let you know how the car did. Sure read a lot here thought that says what you do up front effects the rear and vice-versa...........so by tightening up the front with the M030's, Petes brackets and the Delrin bushings............I should be tightening up the rear also.

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[pure&simple]

>> My alignment is 1 degree Camber in on the fronts and right at 0 at the rear.

I think your times could improve quite a bit with different alignment settings. First, the full degree of camber difference between the front and rear could be the cause of your oversteer. If you added more negative camber in the rear and left the front alone, you would see less oversteer. Second, you could run a lot more negative camber, even for a street-driven car, and you will find this will decrease your tire wear on the outer edge. For reference, the camber settings I use for street/drivers ed are -2.0 front and -1.5 rear.

>> I found a few 9" Boxter wheels on Ebay which will allow me to run 255's up front and rear.

Running wider tires up front will increase your oversteer problem.

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[flash]

more negative camber is not as needed if you add the lower brace - that is exactly what it is there to take care of - it prevents a lot of the camber change under load

i am now running about 1 degree negative - now that i have the brace and the huge swaybar, as well as the 255s up front, i am seriously contemplating going down to about 1/2 degree negative, as i just don't get to the outside of my tires like i used to

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[RS Barn]

I agree on camber. you should have at least -1 degree in rear.
What is ride height front and rear? If rear is too high , there won't be enough weight on rear.
See attached simple chart.
Pete

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[flash]

yup - the rear should have about -1

i am still trying to figure out how to reduce my rear negative camber toward -1, as i am maxxed out at -1.9, due to the lowering, 285s, and the offset i am running - i don't get anywhere near the outside of my tires as it is though, which means i am not getting the full contact patch area on the loaded tire, and even less on the unloaded tire

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[pure&simple]

>> i don't get anywhere near the outside of my tires as it is though

I have the same problem on my 255/40 rears, but I absolutely destroy my 225/45 fronts. Even with -2.0 front camber. That says to me that I have more rear tire than I need.

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[flash]

or that you have something else going on:

could be too much front braking relative to the rear - this would cause front loading in corners - bad

could be too much front weight relative to the rear - see above

could be too much tire flex - this would increase tire heat in a corner - bad

could be too much rear body roll - this would tend to push weight to the outside - bad

rear ride height could be too high relative to the front - this would transfer too much weight to the front - bad


of course, by nature of design, porsche screwed up when they applied the staggered wheel concept to this car, just because the market was used to seeing that - they really should have gone with same size wheels and tires all around - consequently the fronts get abused more than they need to

what bias valve is in the car?

what brakes?

what tire pressure are you running?

what is the ride height front and rear?

chassis first - then springs - then brakes - then sway bars - then alignment - then tire pressures

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[wiseman]

Well I obviously have some sorting out to do..............but I am going to order the Koni Sport Yellows for the front to match the rears and am going to replace the front springs to 225lbs. while I'm in there. I won't touch the rear sway hole untill I try the 255's up front. Yokohama sent me some new ADVAN Neova AD08's to try. 235-40-17 up front and 255-40-17 rear. I'm thinking about running the 255 Nitto's up front and the AD08's on the rear and see what that gives me.

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[Tom030]

"kept dialing them down 2 lbs a run with the rears always 2 lbs below the fronts."
See Pete's charts, higher pressure in the front will tend to increase over steer.

"My class winner with R-1's was a 31.1"
If you are 1 second behind the class leader who appears to be running an "R" compund you are right in the ball park.
Figure a 1 second advantage to the R for every 30 seconds of run time.

"944S2 with Khumo Victoracer R-1's"
S-2 has a slight weight and gearing advantage.
Ride with an instructor every chance you get, seat time, seat time, seat time.
~tom

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[flash]

i am not a fan of mixing and matching tires - they behave differently, and it is very difficult to set a balance (and balance is everything) - how they differ in how they handle bumps, side loads, and even temperatures can make for a very unpredictable car - given that you are already trying to sort things out, why add another variable that large?

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[Tom030]

Just read your last post, not a good idea to mix manufacturers, swap the 235's 08's for 255's and keep the brands the same.
~tom

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[pure&simple]

>> of course, by nature of design, porsche screwed up when they applied the staggered wheel concept to this car, just because the market was used to seeing that - they really should have gone with same size wheels and tires all around - consequently the fronts get abused more than they need to.

This is my conclusion as well. My first instructor just went to 295s on all 4 wheels (had to add flares obviously) on his 951 race car with LS1 motor. Says it doesn't push anymore. [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

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[wiseman]

Yea, you guys are right...............I thought about that right after I wrote it. I need to take these things one at a time. Tom030.......Thanks for the tip.....R-1 vs. Non R-1...........I might be closer than I think. Last comment.............looks like I need another alignment but will wait until I get the Elephant Racing Caster Blocks on. Pete recommended I change those those before the Lower Bar. After last weekend, I noticed that I was already getting about a 1/4 inch of wear down the shoulder on the outside of the rear tires at about 36 lbs. Is there any advantage to continue to lower rear pressures ? At what point is too low too low? Maybe I just needed to raise the front pressures?

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[flash]

lol

chassis first - then springs - then brakes - then sway bars - then alignment - then tire pressures

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[Tom030]

There is a book written by Henry Watts called "The secrets of Solo Racing". You should be able to find it on Amazon. It's and excellent tutorial on set up, handling and theory of A/X and time trial. It's been around for years but the information is very applicable today.
~tom

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