In Part 1, we discussed camera placement and capturing data. In this post we’ll explore what we can learn from the data we’ve captured. The track this time is the Shenandoah Circuit at Summit Point Motorsports Park. This is a challenging 2.2 mile, 22 corner road-course used primarily for driver’s education events that features a dimensional replica of the Nürburgring-Nordschleife’s banked Karussell turn complete with 20 degrees of banking (but without the Graffiti).
The configuration in use this day omitted the three chicanes and used the short Range Straight between turns 9 and 11. (I’ve driven more than 40 days on this course and I’ve never seen cars use the chicanes.) It is not a very high-speed course and the walls do seem very close at times, but I really enjoy it, especially in the MINI. This lap at 2:06.75 is about average for me on this weekend. The fastest of the weekend was a 2:04.67. (My best ever in this car was a 2:01.78 but that was on R-comp tires; I was on street tires this weekend.)
Video was captured on a Replay XD MINI 1080 mounted on my rollbar; data was provided by a PLX Devices Kiwi WIFI; positioning was provided by a Dual AV XGPS; and timing came from Harry’s Laptimer (HLT) on my iPhone. The video was edited in Quicktime and later added to the HLT dataset on my iPad.
In this post, we’re going to focus on an examination of cornering speeds. This post isn’t about outright best lap times, rather improving driver smoothness and carrying as much speed as possible through the corners. Lap time is just one of many ways to measure performance. Using data from HLT that was exported to Google Earth, we can plot cornering speeds and lateral G-forces over the track-map. We’ll compare the two laps of this weekend to the reference lap of 2:01 (fastest lap last year in R-comp tires in this car). The color bars are supposed to represent the direction and intensity of the G-forces: Green is 0.4 – 1.0 G; Yellow is 1.0 – 1.25 G and Red is greater than 1.25 G. Our goal for the weekend was to see how close we could come to this level of performance using street tires.
The best lap of the weekend on street tires was a 2:04.67. (The spikes in the data show how much less composed the car was on street tires at these speeds than on the R-comps the previous year.)
Here’s the lap we’re trying to analyze, 2:06.75. Let’s try to find where we’re losing almost two seconds. Lower apex speeds mean lower exit speeds, leading to lower top speed at the end of the next straight. We know that we can’t expect the same level of grip from these street tires that we got with the R-Comps, so let’s look where we might make up some speed.
We can then overlay the 2:06 lap on the 2:04 lap to help see where we’re losing time. The data suggests our theoretical best time is closer to 1:59, even on street tires. In HLT, the image is dynamic so you can drag your finger around the course and see the plots in the data, you can get a similar result using the HLT data export and looking at your laps in Google Earth.
Start with Point A, The Loop. Both the reference lap and the 2:06 lap show an apex speed of 42 MPH which is interesting considering that the reference lap was on R-comps. This shows that there’s a lot of grip on corner entry because of the crown on the road. Use it to your advantage. (This was actually the one spot where the 2:06 lap was better than the 2:04 lap indicating I could have done better than 2:04 had I carried more speed into the corner.) At Point B, the Stone House Straight, I carried a lot more speed into the Hook on the 2:04 lap. As the weekend progressed I gained confidence in braking later, resulting in the same apex speed, but the line exiting Turn 8 was much better in the 2:04 lap, resulting in higher apex speed at Turn 11 (Point C). That extra speed carried all the way to the entry of the Karussel, Point D. Through the Karussel and into the Karussel Esses, however, I actually had better speed on the 2:06 lap since I had a better exit from the banking. (You can see the slight movement to the inside of the Karuessel on the exit where I lost speed heading up the hill — red spike in the wrong direction).
So what’s the take-away from this analysis? I can brake a little later and carry more speed into the apex of the Loop (A). Likewise, I can carry a bit more speed and brake later into the Hook (B), concentrating on getting a good launch out of Turn 9 (avoiding the curb on the inside) to carry more speed into Turn 11, carrying more speed at the exit (C) which will result in more speed at the end of the Bridge Straight leading to the entry of the Karussel (D). In other words: Brake later, brake less. Words to live by.
Next time: Keeping the petal to the metal. Full Throttle. Brake. Accelerate to Full Throttle. There is no “Coast”. And the data will show it.