I finished my first day with the GXP at a high performance autocross training school. I have some GXP handling experience to relate, and maybe some of you can make some suggestions.
I have KW V3 coilovers with a 1.5 inch drop. And the alignment was done relatively aggressively. Similar to Z0K #'s. I did go with a -2 degree front camber. The specs are here.... THE Definitive thread on alignment specs
We played with tire pressures through the day. I was using the stock tires as I haven't upgraded them yet. 39 front 32.5 rear psi.
The car handled really well but still pushed at the limits. I was quite surprised. And I could not throttle lift oversteer the car. The rear was very planted. I could use a bit more throttle lift oversteer on the car at the limit to be able to use the throttle to drive it around corners.
Any suggestions? I did one suggestion at the course and backed off the compression a 1/4 turn (click) on the KW V3's on the rear wheels. I'll see how that goes tomorrow.
The suspension is really doing a great job. The capabilities of the car are up a couple of notches. It cooks on the course. Not much body roll and very nice handling. The rear can really break away hard if you hit the gas and one needs to be careful (at least with stock tires). No rubbing issues at all.
I spun out once. No one told me I couldn't downshift going into a tight corner. I did a poor job of matching the revs. LOL. But I did recover it (no cones hit either) and kept going to an aggressive finish.
IMHO tire pressures of modern street tires makes very little handling difference on an AX course. The stock tires are not designed for hard cornering and as long as they have enough pressure to keep them off the sidewalls they will lose grip long before the car reaches it's handling potential. Pushing in a corner is typically driver induced by driving in too deep and/or at too high a speed. Throttle lift oversteer is typically the realm of the FWD car. That is the difference in the dynamics of the two different ends doing the driving.
__________________
Spin or win, there's no glory for going slow!
Team Dynamics AX racing
2003 GSL, 2005 HSL, National Champion
2007 GXP ZOK Mean
Solo Performance Race catback
Rick Hendrick Pontiac
Solo Performance
CHARLES FRANK goldsmith
theoretically (From my days in the motorcycle world) the higher the tire pressure the longer it takes to heat up (more air mass inside) so you might want to try equalizing the tire pressures to take away some of that back end bite. it might hurt you on the way out when you stomp on it, I run 39's on both ends typically and the car tends to cut loose once it builds boost, especially on seal coated parking lots. I'm sure upgraded rubber would help but I'm using up the stockers while I've got em.
Best thing you can do AFA tire pressures is to pick a pressure (say 39# for the OEM tires as a workable figure) and check them immediately after each run (best to get a decent 0-60# dial gauge pressure gauge with bleed button and use the same gauge each and every time you check pressures). Bleed them down to the chosen pressure if they have gained pressure. That takes another variable out of the equation. Heat in the tire is built up due to tread squirm, also called slip angle, in the turns. If you are overdriving the tire it will build up excessive heat, but that happens relatively slowly with the open block All-season type tread. Street tires start loosing grip pretty dramatically as they heat up, they are usually grippiest when cold. If AXing in the hotter climates 85+ degree air temps you will want to pick up a 10.00 pump tank garden sprayer with hose nozzle at Wally World and spray your tires with cold water to cool them if they are getting hot enough that it is uncomfortable to rest your hand on the tread for more than a couple seconds.
__________________
Spin or win, there's no glory for going slow!
Team Dynamics AX racing
2003 GSL, 2005 HSL, National Champion
2007 GXP ZOK Mean
Solo Performance Race catback
Rick Hendrick Pontiac
Solo Performance
CHARLES FRANK goldsmith
Since you have coilovers.... what spring rates are you running? What size front bar? For my personal driving style I would not be happy with only -2 deg of camber on the front.....
Sodamninsane, course instructors had us lower the the tire pressures on the rear to enhance throttle lift oversteer. With the same pressures on all four the rear was notably more planted than the front and skid pad throttle lift exercises demonstrated that. The goal is to get the car a little more neutral in the early to mid corner. This would help me to throttle steer (by throttle lift or braking) the car. Supposedly the subies understeer so much they run 42,28 F/R pressures to try to get the car more neutral. The car is easy to power oversteer out of corners, but the issue is to get more neutrality on the car in the other aspects of handling (early and mid corner).
Krazed Kanary, thx for the input. We had 65-75 degrees F on both days. Your right that the tires really only got a little warm on these short runs, and it makes sense based on what you say with the open block stock tires I used on the car. I was glad I took this course and started driving the car with stock tires. It allowed me to get a feel for the car at and beyond its limits, learning how in-control the car still is and what options there are to get the car to do what you want it to. And at speeds that aren't at the next level of R-compound tires.
Eric, as for coilover spes, KW notes Front=400 / Rear=285 lbs/inch for spring rates. Nothing else has changed on the suspension (stock GXP stabilizer bars). Most of what I've read here is that the stock stabilizer bars are adequate. I agree that -2 deg camber is noted as notenough for autocross on the car based on what I've read here, but I picked it as a good compromise for my street driving.
This was my first time ever doing any type of autocross and it was a ton of fun. The car is strong in these activities, and everyone should try it. You learn a lot.
Lightening the compression on the rear coilovers one click felt very similar to before, but was helpful. I'd probably want to do a couple more clicks if I get a chance to compare in the future.
The other important thing I found is that the suspension settled quite a bit over the two days (especially the front) and I probably ended up with not enough travel for autocross. The drop was around 2 inches in the front at one point. An instructor thought I was hitting the bump stops at times. I also rubbed the front inner liners a bit, with stock wheels/tires. I raised the front up 0.5 inches and that helped. Even at that, for autocross, I'd probably go with another 1/4-1/2 inch less drop (a drop of 1-1.2 inches) to make sure that the car had all the travel it needed. At least at my current compression settings. I'm hoping that the settling has finished.
Eric, as for coilover spes, KW notes Front=400 / Rear=285 lbs/inch for spring rates. Nothing else has changed on the suspension (stock GXP stabilizer bars). Most of what I've read here is that the stock stabilizer bars are adequate. I agree that -2 deg camber is noted as notenough for autocross on the car based on what I've read here, but I picked it as a good compromise for my street driving.
Any reason you chose that rate split? I could see the spring rates contributing to understeer especially if you're running stock GXP swaybars. Might be worth softening up the front assuming you're happy with the performance at the rear.
I always recommend novices stay on street tires for a full season or 10 events, or until you are consistantly running within the same second on time each run at an event. Driving skill is the major factor in Ax at every level, but especially at the novice level. Pick a median setting on every adjustment and just leave it there for the season. Trust me, there is no adjustment you can do to the car that's going to make any significant difference in your times more than seat time and good instruction. A good driver could drive your car, even if it was straight off the showroom floor, and beat you by several seconds with you driving a nationally set up car.
I've seen more than once Jr Johnson or Sam Strano make some runs with their 3/4T pickup trucks they tow their trailers with on a phase one course at the end of the day and turn times quicker than any of the students did.
__________________
Spin or win, there's no glory for going slow!
Team Dynamics AX racing
2003 GSL, 2005 HSL, National Champion
2007 GXP ZOK Mean
Solo Performance Race catback
Rick Hendrick Pontiac
Solo Performance
CHARLES FRANK goldsmith
Last edited by Krazed Kanary : 04-28-2008 at 04:35 PM.
93AS, no reason. They were the rates that KW chose for the car. Thx for the suggestion.
Good points Krazed Kanary. These may seem obvious, but only to those who have already tried autocross. So I think your post is very helpful for us newbies and those that are going to try it.
Thanks, and you're welcome! There are a handful of basic tips and novice weaknesses I see in most of the novices I instruct that we (experienced axers) tend to take for granted. Let me throw out a handful and see what sticks.
1. driving position! Take the time to get it right then adjust it to that position before every event. Move your seat and/or the back of the seat forwards from your normal driving position. When you place your hands at 10 and 2 on the wheel, your forearm and upper arm should form a 90* angle at your elbow, with your butt pushed back into the crotch of the seat, your feet should rest flat on the floor beneath the clutch and brake pedal with the knees bent and the lower leg perpendicular to the pedal faces. you should not hit the steering wheel with your knees when quickly picking your foot off the floor and onto the pedals. Adjust the steering wheel downwards as low as possible but not so low that your hands hit your legs at the bottom of the wheel. Leave the F-1 driving position for the F-1 drivers it doesn't work for ax! You want to be "up on the wheel" where you can turn the wheel a full 1/2 turn without needing to let go of the wheel or crossing up your arms. Turn your inside rear view mirror parallel with your line of sight or push it up against the roof so it does not block your vision. In ax you look out the top portion of the windshield, you don't want anything blocking your view. (do I need to say it, take down the souvenier panties, air fresheners, fuzzy dice or whatever else you hang up in the windshield?)
Both hands should remain on the wheel at all times except when actually moving the shift lever, even at the start line. That knob is to shift with, it's not a hand rest, and you don't need a head start to find it! I had one student that insisted on leaving his hand on the shift knob while driving. After reminding him of it several times, the next time he did it I simply reached over and put my hand on top his and held it. It was amazing how fast it came off after that. grip the wheel with the thumbs on the inside but you don't need to squeeze it into submission, it's not going to suddenly come to life and jump out the window! Never "palm" the wheel, reach underhand when starting a turn (a habit I had a real hard time breaking), or let go of the wheel and let it spin back by itself at the end of a turn.
Make sure you're pushed back into the seat and your seat belts are pulled up as tight as possible, you don't want to move around in the seat or have to use your arms and knees to keep yourself from sliding. There are different tricks and devices that can be used to tighten your belts. (Unfortunately you cannot use shoulder harnesses or chest straps in a Solstice.)
Next time: where does the course actually start and how do I line up for the start?
__________________
Spin or win, there's no glory for going slow!
Team Dynamics AX racing
2003 GSL, 2005 HSL, National Champion
2007 GXP ZOK Mean
Solo Performance Race catback
Rick Hendrick Pontiac
Solo Performance
CHARLES FRANK goldsmith
I had one student that insisted on leaving his hand on the shift knob while driving. After reminding him of it several times, the next time he did it I simply reached over and put my hand on top his and held it. It was amazing how fast it came off after that.
AX lesson #2-
Know the course! There is no such thing as walking the course too many times, arrive at the event site as early as possible, as soon as the gates open. Do as much car prep as you can at home before the day of the event: empty all personal belongings, organize your gear you are bringing (search here for a list of gear to bring) into logical groups and put each group into a separate HD garbage bag and twist tie closed (makes unloading and finding items easier, keeps things dry should it rain).
Then unload and set up your paddock (pit) spot as quickly as possible, preparing your car to run. Find out how tech inspection is done and get your car thru tech. Now walk the course as many times as possible, preferably with an experienced AXer, not with a group of friends. This is the time for concentration and analization, not socializing. There will be plenty of time for that later. If the event sponsors don't provide one, it is to your benefit to draw a map of the course for reference, so bring a pad and pencil with you on the course walks. Try on the first or second walk to determine which cones can be ignored (usually there will be quite a few that don't come into play in determining the driving line) and which are the critical cones. Group cones into elements and simplify those elements. Most courses can be broken up into a few disguised variations on slaloms, gates and sweeper turns. Chicago boxes, lane changes, a series of shallow offsets are all examples of disguised slaloms. Once you have seen thru the disguise you have eliminated quite a few extranious cones and reduced those elements down into just a few critical cones. Recognizing them as a slalom also tells you how you need to enter and drive thru that element. Find the apex of sweepers (any turn greater than 90*) It may be an actual cone or often it may be an imaginary cone somewhere in the turn. Usually there will be a critical cone at the entry and the exit to the turn that along with the apex defines the line thru it. Ask your mentor to help you find those cones.
One memory trick we use is to name connected elements by a term that remind us of their general shape, such as a decreasing radius sweeper we may call a "J" or if it really tightens up then it may be called a button hook. An increasing radius may be named an opening spiral. A series of gates that form a nearly straight line may be called a chute. Slaloms we typically describe by the number of cones we must turn around, how much we have to turn to enter the slalom (<45* entry turn is the "easy way", >45* turn is the "hard way) The distance between cones (25 paces or more = "giant" or big", < 25 paces = "baby" or "little" or "tight") and the placement of the critical cones (in a line, or offset to the easy side or the hard side) So a series of critical cones that will be driven as one element like a slalom may be called "Giant slalom, 5 the easy way, 26 even" or a Chicago box may be called "box, 2 hard, tight 16 opens 20" Immediately a mental picture flashes into your mind and you know exactly what's coming next.
By this method we can simplify the course into 6 to a dozen elements that are easily remembered and visualized. Next we will walk the course a couple more time "seeing" those elements locating the critical cones and implanting that image in our memory. Now close your eyes and picture those elements and cones as you recite the course description out loud without pauses to think about what comes next. If you run into a hesitatin, check your course map and/or walk over to that part of the course and review it from the previous element. When you are able to recite the entire course without pause or mistake, like you are reciting the words to a song or a nursery rhyme with your eyes closed and no peeking, you are ready to drive!
__________________
Spin or win, there's no glory for going slow!
Team Dynamics AX racing
2003 GSL, 2005 HSL, National Champion
2007 GXP ZOK Mean
Solo Performance Race catback
Rick Hendrick Pontiac
Solo Performance
CHARLES FRANK goldsmith
Not much body roll and very nice handling. The rear can really break away hard if you hit the gas and one needs to be careful (at least with stock tires). No rubbing issues at all. 
