No, it's not video, but I thought this might still interest some of you. For reference, here's a track map:


And here's a datalog of two laps of Cal Speedway that I recorded last week (using the DL90 from Race Technology). The black and red lines are my speeds during each lap (Lap 1 and Lap 2, respectively), and the purple line is the lateral g's recorded during Lap 1. I've marked some portions of interest with letters. The plots start and end at the Start-Finish line.


A: Max speed of about 135 mph attained just before turn-in into the oval Turn 1. I am flat out from here to point C on both laps. This is about 8800 rpm in 5th gear.
B: Max lateral acceleration of about 1.25g experienced at ~130 mph. Speed is being scrubbed off slightly despite being flat on the throttle. (This is a very exciting ride in a car with no rear wing or spoiler!) Notice I got a better run through here on Lap 2, carrying a couple extra mph all the way from A to C.
C: Just touch max speed again at the exit of the oval Turn 2 before heavy braking for the infield entrance chicane.
D: On Lap 2, after the first infield hairpin, I completely missed the 3-4 shift. On Lap 1 I didn't, and moreover I stayed flat through the chicane.
E, F and G: Classic example of "in slow, out fast". Having stayed flat through the chicane on Lap 1, I eased off and trailbraked through the right-hand hairpin, getting a great launch onto the infield straight. However, on Lap 2 (perhaps still flustered from my missed shift) I pushed too hard at the hairpin entrance, and ruined the exit. I lost a solid 5mph relative to Lap 1 all the way from F to G. Note: the only evidence of the chicane on the back straight is the big jump in the lateral-g plot between F and G. This chicane is also taken flat out.
H: Clearly overbraked here on Lap 2.
I: Interminable double-clutch upshift from 4th to 5th clearly visible. I have to do this because my 5th-gear synchros are shot, and the gears grind horribly if I shift normally (even on the street).

So which lap was faster? You probably guessed Lap 1, and you're right -- but not by much. Despite all the mistakes in the infield, my higher speed on the oval in Lap 2 made for a lap time only 0.4 sec slower! For reference, Lap 1 came in at 1:58.5.

Overall, I didn't get as many laps as I'd have liked, mostly because I was pushing too hard and had, ah, a couple incidents. In fact the second incident was on what would have been Lap 3, and involved a big, smoking, hairy spin right about point B! Suffice to say, that ended my day while I was still clearly working out the infield. Nevertheless, I can't wait to get back there and tame this monster of a track. It's really a thrill to drive.

 

Very interesting write up and graph. I didnt hear about the spin in T1. That must have been a hair raising experience! How controllable was it? Did you scrub speed quickly?

 

Very instructive John. Thanks for posting. We should all have these so we can compare setups. It's interesting that in the right-left corner at the end of the infield straight (point H) where you thought you over-braked, you caught up back equal by the next corner, presumable because you could get on the gas earlier and accelerate harder, though need to look at more laps to be conclusive.

This seems even better than section timing and would be good for comparing different lines through, for example, the first hairpin (double vs single apex).

 

[QUOTE]Originally posted by davepk
Very interesting write up and graph.

 

how close to the wall did you get?

 

When the rear let go was it a snap spin, or did you have a chance to catch it and it got away?
Was it due to a track condition, driver input, or just too many Gs?
What tires are you running?

Thanks for the info! I'm hoping to avoid a similar fate some day.
- Michael

 

uckerfactor:

 

Rear set-up may have been too soft??

 

The rear let go? You still running with out the rear bar? You dont have a wing on the back correct? Wonder if the areo lift was what did it.

 

Yeah, no wing and no rear bar. Still not sure exactly what happened. Aero lift at the rear was certainly a factor, as was, probably, old tires. Felt like I hit a minor bump, and that was that. Maybe I touched the apron, maybe I twitched my hand on the wheel, maybe I lifted unconciously -- hell, maybe I was just going too fast! Wish I'd had video; but, then, probably better that my wife never see it.