Third Autocross: My first parking lot autocross.

 On September 22 2024, I had my first parking lot autocross, and it was a great experience. I was a little nervous coming into it because I had never driven a cones-only autocross, and this added a new layer of complexity. Racing on a kart track like Daytona allows you to memorize the corners and the racing line by navigating inside the tarmac. Cones have infinite lines. Since all of my racing experience has been in actual tracks, this was completely new. It was a lot more demanding than expected, but luckily I made it through.

Tracking cones is a lot more demanding than I expected, and at least for now, my brain isn’t fast enough for me to think about the line and also look at other sources of feedback, but I am sure as I get more experienced I will get better at this.

This race was the debut of the ApexPro data system. I would love to say that it was a spotless debut, but it wasn’t. I had a lot of trouble getting the video and the data to work at the same time. This meant that I had no videos and lost the data from the three middle runs. For the last run, I turned off the video, and the data worked great. There is still a lot of useful info on the data from the first two runs that will surely make me and the challenger faster.

The day was sunny and hot, the Air temperature was 86F, and the track temperature was 95F. Since I was in the first group, the track was dusty. In general, tire temperatures were lower than you achieve at Daytona, with most runs having the tires in the low 100s. I also chalked the tires so I could see what percentage of the tread I was using. As you will see in the setup sheets I will upload with this post, in general, I think the tire pressures at 38Front and 35Rear are good for tire performance in these Florida Summers. 

The Course

The course was in the parking lot of Publix Field in Lakeland FL, The start was about 30 yards before the timing beam, and it was in a tight left-hander. The CFR SCCA does this to reduce the impact of the launch, which is cool. There was a right sweeper where we got the maximum speed and a slalom, then a left sweeper into another slalom and into another sweeper. The third slalom was the same as the first one, but you left it into a right sweeper, and then you had a tight left sweeper into the finish beam. It was a fun and twisty course where handling was tested and power was not very useful. If I have some time I might try to get this course into Optimum Lap or Lapsim to see the sensitivities but work is very busy so no promises.

Tire Summary:

Front Left: 

Front Right:

Rear Right:

Rear Left:

Left is the newly marked tire; right is the tire after the first run. You can see that the chalk lines are erased in all of the usable thread; this means that the whole tread is being used but it’s not going into the sidewalls. These BFG tires have very stiff sidewalls since they’re the extra load version to be able to handle the 4000lb Challenger. You can also see in the after photos that there is a lot of dust on the track and that the tires picked up all of that dust; this will affect the contact surface and reduce the overall grip. Temperatures from the runs were in the low 100s range which might be a little cold for these tires, but they seemed to be in a decent range for pressure.

Data:

As I mentioned before, I still have to get the video from the ApexPro to work; This also meant that I only have data for my first and last runs. I’m still very impressed with the data I obtained. You can download a CSV version of the data files for both runs here. I also managed to get some good insights from the data:

I got some interesting curves from both of them and I see many opportunities for improvement. Having these through the whole session would have allowed me to improve on the fly between runs, but I am sure all will be getting sorted for the next Autocross. The red trace is the first run (40.758) and the blue trace is the last run (38.040).

The most useful data source, and the one I will probably use the most between runs is the speed vs distance trace. Here a lot of mistakes are visible. You can see that I could have been more aggressive coming out of the second sweeper. I also could have more rhythm and maybe part throttle during the slaloms (I really need to improve my slalom technique). Also in the fourth sweeper, I could have been more smooth in my inputs. It seems like the rear end stepped out, and I had to compensate by lifting. It is also visible that in the last braking zone before the fifth sweeper, I braked later and carried more speed than I did in the fast one. Probably a tenth or so in that braking.

Another useful chart is the Longitudinal G vs Distance. Here I can see that the maximum braking acceleration is -0.47G. With tires like this you should expect braking accelerations around -0.9. There seems to be something wrong with my braking technique that I need to address to find more speed. It might be the fact that I’m not going fully straight when I brake which compromises the tire’s ability to grip. Let’s overlay the yaw rate and the longitudinal G to verify…

Here you can see in most braking events, the car is yawing while I brake. Projecting a straight line and braking on it is faster and will provide more braking power, but still there are a couple of good braking events and the maximum acceleration is still way below what is possible. I will find an empty road soon and do some practice 40-0mph brakes to better understand.

The lateral G vs distance trace is also very useful, here we can see that there are places where I could have leaned harder on the car. I also saw a point where I accelerated too strongly and had to lift off losing lateral G and speed and also in the final sweeper there is an oscillation which indicates the my inputs weren’t smoot enough to maximize acceleration.

Video Analysis:

YouTube user Turtlesharkshooter created a playlist of videos he recorded of some runs (Great job, thanks!). Luckily, my run was recorded, as were runs by Eugene Khom in his Mustang Dark Horse and Michale Masser in his Mustang GT. Both ran in the CAM-C class for contemporary muscle cars so similar weights than my car. Both had cones in their runs, but their times were in the 34s, so they are good benchmarks to try to identify opportunities for improvement. He recorded my third run, which was a 39.096. I analyzed it and found two important areas where I can be faster:

The first opportunity I saw was the angle of entry into the slaloms. In that run, I entered with too wide a line, which made me lose time trying to get the car rotated. It is super visible in this video capture. Next time I have a slalom I need to focus on projecting a little bit more and handling it with rhythm. Maybe moving my eyes further forward will help.

Another opportunity I identified was entering what I call slalom 3, which is the first slalom for the second time. In their case, they braked in a straight line, got weight into the front wheels, and then came into the slalom. I coasted into it and since I had no weight in, the fronts drifted wide, and had to tap the brakes to get the car turned while inside the slalom. The difference in rotation angles is very evident in the second photo to the right.

Results:

In the end the competitive results weren’t too bad. I was fourth in the Novice class. I still need to find 3s to be able to be competitive once I graduate to my actual class. I had five runs with no cones, and reached my performance reasonably quickly. My max performance still needs work, but that just means I have to work a little bit harder on improving my technique and finding those tenths of a second. For the next event I will try to look at my braking technique and maybe my brake hardware as well as looking at my alignment and finally getting video of every run.

As usual,

Here is the link to the setup sheets and notes from the event.

For the next blog I will see what is happening to my braking.