I was at the NCRC trackday at Reno-Fernley Raceway last weekend when I got some first hand experience of what happens in a high speed spin. I was coming down the front straight at well over 100 mph and slowed slightly to take the esses that make up turn 1. Now on the track map they may look like fairly severe turns but in actual fact you just lift a little bit to settle the car at the end of the straight before flooring it though S bends. On this particular lap I came in a little hotter than on my previous runs and just after i made it though turn 1 (but before 1A) the back end came around and I flew off the track at 95 mph.
People have asked me if my life flashed before my eyes but in reality the only thought that went through my head was “Please don’t flip!” :-). The car was surrounded by a massive dust cloud which meant that I had zero visibility – I had the sensation of spinning and slowing down but had no clue as to which direction I was heading. As is standard practice during a spin I “put both feet in” (hit the clutch and brake) to ensure that the car has a predictable trajectory so that other drivers can avoid it. It probably took about 30 sec to a minute for the dust to settle but it felt like an eternity as I had no idea where on track I was or what the condition of the car was. Once the dust settled I found that I was in the sand/gravel trap about 50-60 feet from the left edge of the track and having done at least one 360, pointing in the correct direction. I started up the engine but since I couldn’t actually see much of the road in front of me I backed the car up about 10 feet. Moving the car turned out to be an excellent idea because the dried grass under the engine bay had caught fire and when I moved I could see that the spot I had stopped in was actually burning (maybe 4-6 inches on flame). I then waited for a couple of the cars to pass before slowly driving through the gravel trap and rejoining the circuit. The car initially felt fine but as soon as I took a right turn I found that the steering was pulling to the left. While I initially feared suspension damage, by the time I got to the pits I was pretty sure that it was a flat in my left front tyre.
Examining the wheel in the pits showed that the flat was due to the tyre popping off its bead rather than an actual puncture. I borrowed a jack and pulled off the tyre before inflating it and reseating the bead. Luckily the wheel had no damage and the tyre held air with no leaks. I also checked for suspension damage but thankfully everything was solid. Now that the my greatest fear was passed, I examined the rest of the car for damage and amazingly the only other issues were a broken mirror on the drivers side and some minor paint chipping on the drivers door. The car itself was absolutely filthy with a thick layer of dust coating every square inch of the interior and exterior. I knew that going into the gravel trap would be dusty but never expected it to be this bad – my passenger commented that it felt like a dump truck had poured a load of dirt into the cabin. I drove into local car wash during the lunch break and washed the exterior of the car before spending a small fortune on vacuuming the dirt out of the interior. In about 2 hours time the car was most back to normal and looked like merely a dirty car rather an absolute write-off.
Since this was my first track day with a DL1 data logger, I actually had detailed logs to help me diagnose what exactly went wrong in the corner. The first diagram shows the line I took through turn 1 while the second is a graph showing the speed and longitudinal G force plotted against distance. The red line is the lap I went off on and the black line is data from my previous flying lap. The first thing I noticed that my speed down the front straight was significantly higher than on that lap (114 mph Vs 107 mph). This meant that when I lifted to set the car up for turn 1 it took longer to get to the right speed and I ended up going into the corner a bit too wide (figure 1). As a result of this the car got a little loose through the turn and I instinctively lifted of the throttle just a tiny bit (figure 2). This created a classic case of lift-off oversteer where the weight transfered to the front wheels causing the rear to lose traction and come around. I have experimented with lift-off oversteer before and even use it at autocross to rotate the car but this was the first (and hopefully the last) time this has happened to me at such a high speed. It was a pretty scary experience and happened so fast that I had absolutely no chance of catching it – all I could do was hold on and hope for the best.
In the end I was extremely lucky to walk away from a near triple digit spin with nothing more than a broken side mirror and a very dirty car. Having the DL1 was extremely useful in diagnosing the issue (especially since I don’t recall lifting but the data doesn’t lie) and gave me more confidence about going back onto the track. The next day I was back on the track and while I was initially a bit gun shy of turn 1, by the end of the day I was taking it at regular speed. All in all it was a very educational experience and reinforced the need to follow the mid-engine car drivers mantra – “Don’t lift” :-).
Update: I’ve posted this as an EliseTalk thread that is getting some interesting feedback and ‘confessions’ 😀
[tags]trackday, Reno-fernley, oversteer, spin, 360, DL1[/tags]