:. Racing .:. 2005/04/09 - Autocross
Bad Day to be a Lefty:
The first summer series autocross in the RM region is always a little bit of a circus. In years past, it's been due to the 300+ people entered. This year, it was due to cars breaking.
Weather for the day was nice - right around 60*, without much wind for most of the day. Rain threatened in the afternoon, but we never really got hit with it. What we did get was a spectacle of rain and rainclouds against the backdrop of the Rockies, with sun shining all around the clouds while it happened. Colorado is truly a wonderful place to live.
For myself, in stark contrast to the last solo, my day was completely uneventful. I unloaded the car, gridded it,
did my runs, loaded up, and went home. Easy racing the way it's supposed to be, and the extra 1/2 hour I get to sleep because of the reduced preparation time is fantastic. As I develop my routine with this car, everything is getting easier, cleaner, and faster than with the 'vette, which was one of my biggest goals: racing made easy.
From last time, I'd made a bevy of changes to the car to try and improve the handling of the car, and to try and help it cope with the bumpy DIA lot a bit better. Changes are listed below, as always.
My impressions of the changes were that the car seems to be behaving much better. Included in the changes was also an accidental change from 350/450 spring rates to 350/400 - I had thought I had 350/400, but discovered when I took off the rear springs that they were in fact 450's. Live and learn.
The car still has a dominant steady-state understeer characteristic I'm going to need to fix, but chassis composure is much better. The car handled bumps much better over the rough parts of the course, and I didn't get knocked around like last time. Further, it had none of the skatey-loose turn-in problem from previously, so I wasn't trying to catch slides every time I turned the wheel. The understeer seems to be slightly lessened, so I'm going to try lowering the front of the car a bit more to see if that helps, and doubtless, the R25's should make things feel a lot better in general, next time around.
What is interesting is that the car's turn-in seemed to be quite good, entering slaloms and the like, but it seems to "wash out" a bit after the car rolls and takes a set. This may be a driver issue (gasp!) of too much corner entry speed, shot/cold tires, or something else. There is a noticable period in which the car rolls, sets, and then begins to push. Very interesting indeed. Possible causes of this that Carroll Smith lists are a.) too much toe-in b.) too little bump damping c.) incorrect ride heights/roll axis inclinations. Since these are all things that I know still aren't 100% right on the car, this is encouraging. There is still LOTS of time to be found through car tweaks still, which is a fun place to be.
The runs went roughly like this: First run went OK - I blew through the mid-course 90* right-hander, since it drove a lot sharper than it looked from walking. There was a visual element there that confused me, that I still never got quite right. The understeer of the car didn't help either, since it pushed mightly through that corner every time. Again, this could be a driver issue, but the understeer balance still seems far too much to the 'safe' side of things for my tastes. Coming back up over the hill at the end of the sweeper, I tapped the brakes to get set up for the slalom, and the car instantly spun. As it turns out, the car still has too much rear brake bias from my experiment at the end of the last SCR session, so I'll move it back towards the front a little bit to make braking a bit more secure. A dash adjustable brake bias bar is now high on my list.
Second run was relatively uneventful, other than an AWFUL issue getting off the line. The rich low-RPM bog is getting even worse, now that the weather is warming up. I'm going to have to do something about this soon, or the car's going to be damn near undrivable. I understeered in the same spots, and had some better lines. Still got a bit of a bobble coming up over the hill on the brakes.
Third run, getting off the line was even worse - I hardly was able to get moving until the 4th corner of the course...ugh. Went a bit slower on time, probably because of that bogging issue. Added a downshift in a slow corner, and felt that was a big improvement.
Fourth run, I eased the car off the line, and it finally got going relatively quickly. The run went well, with me braking a bit more carefully and earlier to try and ameliorate understeer. I also downshifted in a few spots I hadn't downshifted previously, and had much better exit speeds from those corners. I learned that I will definitely have to be more active with shifting this car, since it just doesn't have the torque I'm used to in the 'vette. My final run was good enough to grab second place by about 0.5 second, and that's even with accidentally selecting neutral on a downshift right at the finish. So, with some proper tires and a few more tweaks, I should be able to give Evan Brauch a bit of a run for his money next time - we'll see...
So, what of cars breaking? The first is a real heartbreaker - my old Corvette, which Mike has now, blew its motor on Mike's second run of the day. Engine block, con-rod,and oil pan parts scattered everywhere. Big explosion, fire, smoke, the whole nine yards. The engine is obviously trash, but everything else seems to have survived OK. The other car, another LHR member, Lawrence Edwards' S2000, spun into one of the signposts, and now has a square-shaped dent in the right-hand door. Cosmetic damage only, but it won't be terribly cheap to repair, unfortunately. All in all, a bad day for Lefthand Racing.
Next time: New tires, a few smaller suspension tweaks to see if the understeer can go away a bit, and with luck, I can get some tuning done to try and eliminate or lessen that off-idle launching bog.
- Set rebound to nearly full soft (-13/-15)
- Reduced gas pressure from 180 to 120psi
- Lowered car from around 3" ride height to 2 3/8 / 2 3/4
- Set rear bar to hard
- 15T front sprocket versus 16T
- 350/400# springs, from 350/450#