Climbing Up The Mountain

Bathurst 12h at Mt Panorama presents so many more challenges than just "go fast".

Over the weekend George and I ran our first endurance race together of 2023. What a race to choose. Mount Panorama aka Bathurst is very much an old school track. It is made up of public roads and like many mountain roads it is twisty and there are no runoffs. Adding to the difficulty George and I mostly drive prototypes and this race was is only GT3 cars. iRacing gives each driver an iRating that is used to divide up drivers of similar speed. When racing in a consistent series or car this works pretty well. But for George and me, iRacing thinks we are quite a bit faster than we are in GT3 cars.

Watch the race here.

The Mountain

Bathurst can be thought of as two tracks grafted together. One half is made up of long straights connecting the pit straight to the other half of the track, the mountain. Figure 1 is an elevation heat map on the track map. The start finish / pit straight is in the lower right

Figure 1: Bathurst Elevation

corner and is the lowest spot on the track. Coming out of turn 1 the track start climbing, gradually then after turn 2 dramatically. From the exit of turn 2 through the peak at Skyline, top left, the track rises over 100 meters at over a 10% grade. I feel like most tracks try to put the really steep sections of the track going up hill but not Bathurst. After cresting at Skyline the track turns down, again at over 10% till Falken corner, lower left. Figure 2 shows the elevation slope. And as a slow driver my minimum speed is still always above 100kph and often over 150kph. Finally, as the image at the top shows, the walls are close.

Figure 2: Bathurst Elevation Slope

Race Prep

All of the iRacing GT3 based series were also racing at Bathurst last week. George and I were able to get a decent amount of practice and he did one race before the 12hr. Unfortunately two conclusions were obvious, we were off the pace and we had to keep the car out of the pits as much as possible. George was for sure faster than me but both of us were off the pace. Figure 3 - 5 show raising lap time plots for our pre-race work.

Figure 3: Raising Lap Time, Sam Practice, 50C Track Temp

Figure 4: Raising Lap Time, George Practice

Figure 5: Raising Lap Time, George Race, 20C Track Temp

Knowing my pace was well off I spent most of my time just lapping to do everything I could to be smooth, consistent, and out of the pits. Figure 3 is a little over 1.5 stints of continuous lapping.

Keeping the car off the walls would help keep us off out the pits but watching our fuel strategy would too. The BMW M4 GT3 that we used had a fuel stint length of 28 or 29 laps, which based on the average lap time would result in about a hour stint. Figure 6 shows a heat map for number of stops based on average lap time and average fuel used. Figure 7 is the number of expected race laps with the same parameters. Our expected lap time and fuel usage was 1:27.25s and 3.6l/lap respectively.

Figure 6: Number of Stops

Figure 7: Expected Race Laps

Figure 6 and 7 show that we were likely well within the 11 stop race range and that there is a small increase in the number of laps if we can reduce our fuel consumption from 3.6l/lap to 3.5l/lap without a significant lap time increase. This amount of fuel saving was achievable with lift and coasting for 100m into the penultimate corner. Going into the race our objective was to stay out of the pits and target less than 3.6l/lap of fuel.

Race Results

I feel like I have already hedged pretty hard that George and I were going to be out paced. With our average iRating of 3.5k we were placed in the 7th of 30 splits. The lower the number the "faster" the split. George's race shown in Figure 5 was race with an average iRating (strength of field, SoF) of 2.6k. Now that I have thoroughly hedged our relative pace I can get into the race results. George and I are racing under the name Backroad Bandit Racing Black (BBRB), our times will be bolded when comparing to other teams.

George qualified 42nd out of 49 cars and started the race. The beginning of the race was pretty chaotic, someone crashed before the green flag. Also, because were so far back the race started well before the final corner. George drove really well and avoid getting caught in a pile up going down the hill. After his first stint, ~lap 28, we were not moving forward very fast but we were still running with the pack. Figure 8, below shows George and my first stints

Figure 8: Gap to BBRB - Laps 1 - 60

and the gap that we had to the other teams over that time. Based on the slopes of the gap lines George was immediately faster than me. Unfortunately, in my second stint I was feeling internal pressure about not being faster and while pushing lost control of the car at the top of the mountain. The lead team was also lapping us and I was very concerned about not taking the leader out less than a quarter into the race. We ended up losing about 250 seconds, a little over two laps, and George took over.

Figure 9: Gap to BBRB - Laps 1 - 150

The end of the first third of the race was not great for us. George also lost control on about lap 120 going up the mountain. This lost us over 600 seconds, a little under 5 laps.

Our final loss of luck came around lap 150 when George got tagged going into Falken corner and we lost another ~200 seconds, 2 laps. Figure 10 shows our gap after lap 200, a little over halfway through the race. We were over 8 laps behind the leaders and one of the last cars still running. We agreed that if we ran into any other problems we would just call it.

Figure 10: Gap to BBRB - Laps 1 - 200

Thankfully the second half of the race was surprisingly quite. George and I drove consistent incident free stints till the end. Unsurprisingly we finished 21st overall and the last car still running. Figure 11 shows the final gaps. We finished 12 laps behind the leaders.

Figure 11: Gap to BBRB - All Laps

The gap figures, 8 - 11, show we were off the pace but it is not until looking at the lap time deltas, Figure 12, and rising lap time plots, Figure 13, that the deficit becomes obvious. Both figures show that we were losing about 1 second a lap to most cars. George and I are pretty competitive and this was pretty challenging to drive through.

Figure 12: Lap Time Delta to BBRB - All Laps

Figure 13: Rising Lap Times - All Laps

Something that is very interesting and a bit consoling about Figure 13 is that the team that won, GazX Racing Team 888, were almost always a second faster then everyone else. The team Bathtub Bois was leading through the first third of the race, and was the only team near the pace of GazX 888, but crashed shortly after lap 100 and sealed the deal for GazX 888.

We ultimately lost between 6 and 8 laps in the pits, had we not lost that time we would have likely finished in the middle teens. Overall a bit of tough result to take but I think both of us walked away from our first race endurance race here happy with our ability to just keep going and not let some small mistakes ruin our chances to finish a very challenging race.

The race started before dawn and finished just before 6pm local time. Because February is the summer in Australia we expected the track temperatures to be very high throughout the race. Figure 14 shows the track temperature starting at about 21C, climbing to over 50C and

Figure 14: Track Temperature

finishing just below 30C. We were changing tires every stint because they could be changed when fuel was being added and we would not lose anymore time. This was less critical at the beginning of the race but as the temperatures got above 35-40C the front tires would start complaining and some tire management was needed in the first half of the stint. I think this can be seen in Figure 15, below. There is a noticeable rise in lap times and then as the track starts to cool, the lap times start to go back down again.

Figure 15: Lap Times by Lap Number - All Laps

As I have said above George was faster than me throughout the race and this becomes easier to see when I pull just our lap times out of Figure 15. George is the blue line and I am the orange in Figure 16 and visa versa in Figure 17. George was almost always about a second faster than me. The ends of my stints were much more similar to the starts of his next stint than they were to the ends of any of his stints. This is something that I have noticed about driving GT cars, I have a hard time sliding them correctly to really extract all of the pace. In the Audi LMP1 George and I were similar, so I don't think it is just that George is faster than me, he's just better at GTs than me.

Figure 16: BBRB Teammates Comparison - Lap Time

Figure 17: BBRB Teammates Comparison - Rising Lap Times

The final teammate comparison figure is below. Figure 18 shows the rising lap times for each of out stints. I am not sure why the processor is grouping George's first two stints together I have not found it doing that anywhere else and summing the number of laps returns the correct value. It looks like my pace is a bit more consistent over the length of the race and stint but this is really a small technical victory.

Figure 18: BBRB Teammates Comparison - Rising Lap Times per Stint

Closing Thoughts

Going into this race we both knew it was going to be a struggle. We knew that the track was going to unforgiving and that we did not have enough experience to really find the last tenths out of the car. But still it was a really good feeling to reach the checkered flag at the end on 12 hours knowing that we gave it our all.

With season 1 of 2023 coming to a close in the next few weeks I am going to try to get at least one more race on the YouTube channel and debriefed here. There are two track that I like, Sebring and Road America, hosting the BMW LMDh this week and next. I would really like to be able to do both of them. I am not sure if George and I are able to do another endurance race this season but we are planning on driving the BMW LMDh in the 12h of Sebring on March 25th. Hopefully that will be a more competitive race.

I am still trying to work on a hybrid regen optimizer for the BMW LMDh but I have barely had time to practice much less devise algorithms in the last two months so hopefully there will be more development on that front starting next season.

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.

Auxiliary Data For Nerds

This section has a few more rising lap time figures. This time they are broken apart by car. George and I are included on everyone for reference in black.

Figure 25 shows our times relative to the other 25 BMW M4 GT3s. This figure hurts a lot because our pace was even outside of one standard deviation. If that doesn't say we were not in the correct split or familiar with the car I don't know what does.