Last week I wrote about the ChumpCar race at Thompson. This week I want to take a look at the telemetry we recorded with an Aim Solo. As a reminder, this is what the track looks like.
The first thing I want to explore was the difference between my practice and the race. My fastest race lap was more than 2 seconds faster than my practice. Why was that?
The top panel is speed. The next two are G-forces. The bottom is time difference. I don’t tend to find the G-force graphs very useful.The black line is the “reference” or fast lap. The red line is the practice lap.
If you look at the speed graph, you can see that I’m pretty much faster everywhere. I’m braking deeper into the corners, and I sometimes have lower speeds in the middle of the corner (actually slightly before the apex). I knew when I was driving my fast lap that I had pushed too hard at point A and was understeering badly. This turned out to cost me about a tenth, so it wasn’t that bad. In order to get into the 1:26s, I’ll have to find more speed. So let’s look at the other drivers to see what I can learn from them.
I brake later and carry that speed much farther into the corner. By the time I’m on the gas, I’ve gained over a second on the green and red drivers. But I’m much later getting on the gas, and that advantage starts to decay. If there was a long straight following T1/T2, they would catch and pass me. However, on this track, my strategy would allow me to pass them going into T1 and block them on the way to T3. I brake later and keep more speed through T3.
Despite my more aggressive driving style, I’m no faster than the blue driver, and the red driver has mostly caught me by the time we fully exit T4. At some point I’m going to gap them by 2 seconds, but it isn’t through these slow corners. T5 has a funny data error; ignore that. I brake much, much later in T5 and carry the same exit speed. So I put some distance between myself and the red/green drivers. But the blue driver has a similar line to mine and we’re still neck-n-neck as we head toward the bowl.
In T6, you can see that I have the lowest mid-corner speed. I took a lot of different lines through here and this one wasn’t that good! By the time we are running down the straight between T6 and T7, I’m not much ahead of the red or blue drivers. What happens next is critical.
The red and green drivers brake much earlier. They have a somewhat constant rate of deceleration all the way to T8 and then pick up throttle from there. Without a throttle or brake trace it’s hard to say if they are coasting, but my bet is that after some initial braking, they are scrubbing speed by coasting. Coasting is generally not the fast way around the track, but it does have its uses. In contrast, the blue and black drivers have a roller-coaster speed trace. They brake much later on the way to T7 and speed up between T7 and T8.
The blue driver is losing nearly 2 seconds by overspeeding between T7 and T8. He ends up turning T8 into a braking zone. His speed never recovers and he ends up with the slowest speed down the main straight. This is a Miata, not an M3. The throttle is a suggestion to go faster. You have to keep as much speed as possible, especially in the fast corners.
Thinking back to last week, I was really excited about this series of corners. It’s a Type II followed shortly after by a Type I. That is, you brake way late for T7 to keep as much speed as possible. Then you throw away the exit to set up for T8 with just enough speed that you’re full throttle from just before the apex until the end of the main straight. That’s what I did, and it’s 2 seconds faster than the other drivers. That said, even if the others had taken my same line, they are unnecessarily lifting or braking to set up T9. That section is really about confidence more than technique. They’ll get faster as they get more laps.
3rd Gear Experiment
Late in the day we started losing the clutch. So Mario decided to do an entire stint without using 2nd gear. The results are pretty surprising.
The black line is his reference lap (fastest 2nd gear lap). There are two 2nd gear corners: T1 and T4. Once you hit T5, it’s 3rd and 4th all the way. So let’s look at the time and speed through T4. Amazingly, the loss is only 0.2-0.3 sec. In T1, he consciously holds more speed in 3rd gear. While he doesn’t get as much drive leaving the corner, he loses no time to shifting. The net effect is that he has lost no time by the time he hits T3. He does lose a couple tenths in T4 though. It’s a really tight corner, and 2nd gear puts the power down much better than 3rd. But it’s just a couple tenths. OK, so I’m driving in 3rd next year, at least in T1.
GPS Alignment Issues?
One of the YSAR readers, Sten, who happens to be a data analysis professional, claims that “some of the data is definitely misaligned”. I admit that I suck at telemetry analysis, so I followed up with him. Over email he further specified that it was impossible for the black and green lines to be accurate in T1 and T3, for example. Here’s an overlay showing the 5 fastest laps from the black and green drivers. They are fairly consistent.