Indoor Karting With A Shifter Kart

First race in six weeks. First race with the BMW LMDh. Frist race at Long Beach. What is the worst that can happen?

Image from racedepartment.com

Watch the race here, beware spoilers below.

With the holiday season and a few weekends out doing winter activities I have not had a lot of time for iRacing. But this week I saw that the IMSA series was at Long Beach and I had some time to practice so I was finally able to give the BMW LMDh and Long Beach a go. Throughout the week I had not been focusing very much energy on lap times, although I think I'm probably in the ~1 second off the pace range, which I'm ok with right now. Being a new car and a street coarse I was primarily focused with turning consistent laps and doing long runs in practice. I did grab a setup from Majors Garage but I am incapable of leaving well enough along and messed with it a bit.

Long Beach Track Map

Pre-Race Preparation and General Balance

I find this car has a decent front end if I carry the brakes all the way down to the apex. Unfortunately, I don't feel a lot of confidence in the rear while trail braking. I also feel like the driveline is very willing to spin the rear axle, and then the car, coming out of corners. I think these characteristics are somewhat foundational to the car but I also think my current driving style and unease with the amount of phase 1, 2, and 3 oversteer are heightening these issues.

I need to do more analytical work on this in the future but I think I am likely rolling off the brakes too early and or fading into the corner to early to reduce the amount of cornering force I am asking the rear to oppose. By rolling off the brakes too early I am allowing the front axle to raise and unweight resulting in phase 3, and 4 understeer. This will also result in me needing to "over slow" for the corner because I am not generating as much cornering force as I could if I were to keep the front planted.

By fading into the corners too early I am able to elongate the corner and reduce the amount of anti-rotational force the rear axle needs to provide. However it is every easy to not have enough rotation in phase 3 and square off phase 4. The lack of rotation will also extenuate the perception of understeer mid corner. It is also likely that I will continue to over slow and not be able to get onto the throttle until very late in the corner. Which leads to my final major issue.

By getting on throttle very late in the corner I want to get on it very hard. By not rolling onto the throttle more genteelly in phases 3 and 4 the engine will provide for the large torque request and help spin the rear axle. By being able to balance the car better on corner entry I think I will be able to reduce mid corner understeer, over slowing, and exit oversteer.

In order to combat this I changed a few things with the setup. I reduced the rear ride spring stiffness, reduced the rear ARB stiffness, increased the front and rear low speed compression damping, moved the brake balance forward, and reduced the preload on the differential. I think I am giving up time by softening the rear axle but I am willing to loss some time in order to help keep the car off the walls. While I was driving I would also try to focus on not letting myself turn in early, riding the brakes all the way down to the apex, and slowly roll onto the throttle. I was only focusing on improving these three things because they apply to almost all of the corners and I have found I can only focus on improving two or three things at a time before I am overloaded and not focusing enough on driving.

Figure 1: Hybrid Modes, Attack v Balanced

An unrelated but interested thing I noticed during practice is that Long Beach has too many brake zones for the hybrid system. Figure 1, above, show a table comparing a balanced hybrid mode, first stint, to an attack hybrid mode, second stint (Balanced targets 50% SoC every lap and Attack targets 0% SoC). I default to a balanced mode in practice, especially when I am not going for lap times, because it is more similar to racing conditions. I want to have a similar amount of hybrid energy to deploy every lap. But I noticed that the battery was almost always at 90%+ on balanced and decided to try leaving it on attack. From Figure 1 it is easy to see that there is almost no difference between the total deploy, channel: EnergyBatteryToMGU_KLap, or the battery change range, channel: EnergyERSBattery display: Range. Because of this lack of difference I set the deploy mode to Attack and stopped thinking about maximizing the brake energy recovery. Honestly this discovery was welcomed because as I stated above I already had enough things to think about.

The Race

I ended up starting at the back of the LMDh field in 11th. For one, my pace is not amazing. I might have qualified 8th on pace. And two, I made a mistake on both laps and did not get a recorded time. This was not the end of the world, pace wise I was not near the front, I assumed there would be a mid pack turn one crash, and my goal was to just survive because its Long Beach people are going to crash out in front of me.

As I assumed there was a mid pack first corner crash taking people out how were in the 6th - 8th range. Pros for starting at the back because I was able to see and avoid it. Unfortunately, I did get caught behind a slower driver named Mike. I was never able to really get traffic to fall my way to make a move on Mike and I was never able to get a good enough run out of the hairpin, turn 11, to for the issue into turn 1. Because I noticed that I was faster than Mike but I was having a hard time lining any move safer than a divebomb I chose to attempt an undercut. I felt I was faster, I assumed a fuel stop was necessary, we were about to catch the GT3 field again, if I was going to gamble this was the correct gamble.

At the end of lap 20 I pitted and took 8 liters (l) of fuel. I did not come out of the pits with quite as much space as I had hoped. The lead LMDh and lead LMP2 were pretty close to me but overall I dont think I lost that much time. I do know that EJ was right behind me before I pit and come out right behind me after he pit, lap 28. Although I was not able to test my undercut fully because on lap 33 I locked the front axle into turn 1. Hit the wall. Broke the front suspension. And was out of the race with just over five minutes to go.

At the time I was not sure what happened. I did not feel like I missed my brake point and I thought I applied to brakes enough, but obviously I did not. I do not have a figure for this lap because I accidentally turned off the data logger while I was trying to mute the race chat. Looking back through the stream though it looks like I broke at the correct spot just not has hard as I normally did. I also faded off the brakes faster then I usually do. Once I noticed that I was still going too fast I got back on the brakes harder then I should have, locked the fronts, and slid into the wall. This mistake was pretty costly, I was running 6th and EJ, the car behind, ended up finishing 5th. I feel reasonably comfortable chalking this mistake up to driver fatigue. I am still finding it hard to get into a relaxed rhythm with this car and I was already noticing signs of fatigue and small mistakes before the crash.

Post Race Analysis and Other Strategy Options

There are still two big questions that need to be answered before stepping away from this race. First, would the undercut have worked if I had not crashed? Second, is this a no stop race? The person that won the race actually never stopped for fuel. I had a thought, on about lap 3, that it might be possible to go all the way but I decided it would be too tight and I did not have enough bandwidth to focus on my fuel number.

Lets start with the first question. Would I have passed Mike in the pit sequence if I had not crashed? This is a very easy question to answer, no I would not have passed Mike, because Mike did not pit. Of the LMDhs that made it to lap 30 me, EJ, and Matthias were the only people to pit for fuel. This is a pretty obvious strategy error that I did not expect. I think Long Beach is a very low fuel consumption track and this will not be "normal" in other 45 minute IMSA races. That being said I will need to check for it from now on.

Before I move onto fully answering question 2 lets assume that this was a more normal race and Mike had to pit. In this scenario did I make the correct decision? I am going to assume that Mike has a normal pit stop. Based on the handful of other people that stopped it should add about 36 seconds to Mike's total race time. So I need to be within 30 - 35 seconds of Mike within the last five or so laps. I am also going to assume that my laps after I crashed are my non-pit lap average lap time, 1:12.315.

Figure 2: Mike's Gap Ahead of Me

Figure 2, above, shows the gap between Mike and me throughout the race. For the first ~15 laps we are within 5 second of each other with Mike pulling away in traffic and me pulling it back once we had cleared the traffic. Laps 18 and 19 the gaps are basically 0 because I was right behind him. Lap 20, the first spike, is me pitting and losing about 35 seconds to Mike. When I crashed we were just under 20 seconds apart. I would have likely come out of the pits 10 - 15 seconds in front of Mike. If pitting at all was the correct decision, doing it when I did was the correct choice. Figure 3, below is EJ's gap ahead of me. iRacing has some lap timing errors that I am not sure about because this shows EJ in front of me after pitting but I know that I came out just in front. If I would have stayed behind Mike and needed to pit EJ, who I think was faster than me, would have jumped me in the pit sequence. EJ gain time on me after I pitted, laps 20-26, and I was going faster than Mike who would have been holding me up.

Figure 3: EJ's Gap Ahead of Me

Under normal conditions I pitted at the correct time but was no stopping still the correct strategy? I have to think yes. The car that was leading before crashing on lap 35 looked to be planning a no stop. The eventual winner did not stop, and the car in second would have won if they had not stopped. Finally, EJ was 10 seconds behind Mike at the end. Figure 4 shows Mike's gap ahead of me assuming I finished and my last laps were my non-pit average time. I would have still been about 5 second behind.

Figure 4: Mike's Gap Ahead of Me, Assuming I Finish

I took a gamble that would have worked out in other situations. But being a gamble sometimes the situation is not what it seems and it is obvious now that Long Beach in the LMDh with 44l of fuel is a no stop race. The final part of question 2 is pretty easy to answer, what is the fuel number I need to hit to make it all the way? The race I was in was 38 laps so I will fuel for 39 just to be safe. 44l / 39 laps is 1.13l/lap. I was using between 1.3 and 1.35l/lap so I need to save about 0.22l/lap. The best place to find fuel saving is generally at the end of the long straights by lifting and coasting before applying the brakes. I would target starting with turn 1 and turn 9. The fuel flow at WOT is about 0.031l/sec, I will need to find 7.15 seconds off throttle per lap. If I lift and coast for 250m into turn 1, 100meters into turn 6, and 120m into turn 9 I should be able to find the fuel I need. Based on Figure 4 I think going for a no stop could be on the edge of being slower but based on how many other people are doing it I think it will be the way forward at Long Beach.

Closing Thoughts

For my first race in the LMDh, my first race at Long Beach, and my first race of 2023 I did better than I expected. I always want to finish and I always want to win but going almost 45 minutes on a tough street track in a new car after a long break is nothing to be too upset about. I have some good things to take away from this race and some new things to check before each race. Next week is VIR, a track I like but have not raced at in many years. I am excited to head back there and see what new things I can learn.

In the mean time head over to my YouTube channel to subscribe for more races like this. Subscribe to this blog if you like the content here. And if there is something I missed or something you would like me to check out in the future, drop a comment below or shoot me an email in the contact section at the bottom.