Commodore’s Garage #33 – Truck Project: Lucas Oil Raceway

Week four of the Season 1 Class C season is in the books, and this time we actually got a race in with the Truck Project!  Last Thursday Alex Scribner, Jeff Parker, and I all got into the 9:45pm Eastern race and were able to shakedown the truck in a full-bore, “this matters” type of situation and we walked away with a lot of great information.  While we didn’t quite put the smackdown on anybody in the event, we still managed a 4^th place finish with Jeff, I finished in 6^th just a few feet away from a top-5, and Alex finished 11^th after losing an engine following contact with a car that was multiple laps down.  That result is extremely unfortunate, as Alex was in 3^rd place when his power plant let go.  Oh, what could have been…

I put the major changes from Myrtle Beach into a short YouTube video to show how simple spring changes and crossweight changes are without having to make a thousand other changes to correct problems, so if you want to go see that head over to our Facebook page via the link at the end of the article!

Practice Sessions

The setup unloaded quite well with the changes we made, but it still showed some minor teething issues.  The worst of which was the bouncing issue that had plagued us through the entire week at Myrtle Beach, compounding into more problems due to the higher speeds producing a much heavier dependence on aerodynamics at Lucas Oil Raceway.

Something we fought all week was a push in the center, likely triggered by the left-front bounce on corner entry.  I was able to get rid of most of the bounce by running the crossweight even further down, but something in the way we have it configured wasn’t really agreeing with the track characteristics.  We never got it ironed out by race time, however I managed to cure it with some in-race adjustments and get some grip in the center of the corner.  Most of the adjustments I made in practice were simply to “crutch” the problem and mask it for just this track:

• More preload, more bar asymmetry: The left-front corner was hiking up in the center of the corner which would have contributed to the push-loose condition we were seeing at both ends of the track.  The extra preload and asymmetry simply pinned this corner down to get a flatter splitter attitude and free up the center of the corner.  This also required a drop in front ride heights due to the extra vertical stiffness (heave spring rate) from the extra bar asymmetry.
• LF spring from 400 to 420: This added a little more travel in the left-front corner to allow this corner to drop more under load.  This also adds a tiny bit of rate to the suspension to try to absorb some of the bouncing.
• Lower Crossweight, Higher LR spring: Since we had the crossweight so low to iron out the bumps, we needed to increase the left-rear spring rate to raise the dynamic crossweight to something that was more balanced.  This provided stability in banking transitions but likely hurt our long-run performance a little bit.
• Lowered Track Bar: I dropped the track bar equally to give the truck a little more stability for the higher-speed, low-banked entry at LOR.

Something I also tested in the practice sessions was a “double-bind” front-end similar to what Alex used in 2016 on his championship-winning Class B setup.  While the speed was there on a short run, I wasn’t able to get the long-run performance to match the setup with a stiffer left-front spring so I shelved it.  It could make a return tour later, however.

The Race

Our race was fairly eventful, but it was not without minor issues that turn out to be common with first-try setups.  Overall, the balance was good, long run performance was fantastic, and the handling swing wasn’t overly severe throughout the run.  The race started with two short runs, then a very long green flag run, and a final restart with about 10 to go.  Our largest issue by far was an overheating problem.  I started the tape at 55%, which is what we would have run the Xfinity car at a short track in 2017.  For whatever reason, the Truck doesn’t like this much tape at all, so all three of us spent the majority of the race running at a pace that kept the oil right at the maximum safe temperature.  This put a huge damper on how fast we could run, so it’s not clear what we would have been capable of doing had we been able to run as hard as we wanted to during the long green-flag run.

Jeff chose not to qualify and started 11^th, but made his way to the top-5 in the first 32 laps (which included two cautions, by the way).  His pace late in the run matched the eventual winner, but the middle of the race was dictated by the overheating issues.  During the long run, Jeff mostly ran a few slower laps to cool the engine down followed by a few faster laps to make up time.  The lap times when he wasn’t cooling the engine off were very good and it’s very possible that, had he qualified, he would have been running much closer to the leader for most of the race.

Alex Scribner had a strong showing, running comfortably in 3rd place before getting tangled with a lapped car and damaging his truck’s radiator.

Alex had a similar race, however he spent his entire race in 3^rd place nursing his engine.  Once his engine started overheating and he had to back the pace down, he said to me “The pace and balance is great, I could compete with these two in front of me if it wasn’t overheating”.  Unfortunately, we never got to see what Alex could have done because his engine problems got even worse when a lapped car locked up all four wheels on corner entry and slid up in front of him in the center of the corner.  The damage was enough that Alex’s engine expired not long afterwards due to even higher water and oil temperatures.

My race was mostly spent feeling out what the truck was doing instead of racing for anything.  To get a little extra speed at the start of the race, I followed Alex’s suggestion and raised the left-side pressures to 15psi.  This actually wound up making the bouncing worse, so I dropped them back to 12psi during the first caution.  I also made a crossweight adjustment (+0.050 LR, -0.025 RR) during this pit stop to try to get more of the bumpiness out of the chassis.  It worked extremely well for about 30 or so laps before the pressures built up and the bounce returned, but by this time all three of us were overheating and a bouncy front end was the least of our problems.  I did get to really hammer the setup on the final restart and see what it could do since the caution placed me one lap down with only one other car.  It was quite good during that final run, and I even set my fastest lap of the race on lap 102 of 110.  I haven’t pointed this out to him, but my fastest lap was faster than Jeff’s.  At least I’ll know immediately if he’s read this article!

All things considered, it was a great first showing for the project.  Our times were fairly competitive, and according to both Jeff and Alex, it could have competed for the win had the overheating issue been found earlier in testing.  This setup should make a showing again at Milwaukee and Iowa, however I’ll most likely swap which front corner will bind due to the much higher demands for aerodynamics at both of those tracks.  We’ll have to look elsewhere to cure the bumps, but we have enough of a notebook to know where to look and what to do in order to cure all that.

Race Tire Data

Here are the two tire sets I took off of my car during the race and a look at what could be going on.  I didn’t record the data from the third set of tires, which I regret tremendously because I pushed those tires the hardest.

This is the set of tires I started the race on.  It’s worth noting that the left side tires began at 15psi but most of the testing was done with 12psi, so the left front is showing overinflated.  We can also see a slight issue with a little too much crossweight (might be good for that track though), but overall the tires look quite good.

The second set of tires is a little more telling, and this has a lot of good info we can take to Iowa and Milwaukee later in the season.  To start, the left-front was dropped to 12psi and the left-rear dropped to 14psi on the first stop and I also made the crossweight change mentioned earlier.   Interestingly, this crossweight change had almost no bearing on the temperatures for the tire averages, noted by the 10° difference in the Positive and Negative Cross Average for both tire sets.  The right-side tires are cooler by a large margin, but it must also be noted that the longer run wore the tires more and this alone will cool the tires.  This is a sign that the long-run push that developed very late is likely somewhere else in the car and crossweight won’t have a tremendous effect on that.

California Truckin’

Next the series moves to California where we must build a new setup entirely to deal with the different chassis, aerodynamic dependence, and the speeds we’ll see at a 2-mile track.  We can still carry a lot of what we learned at LOR and Myrtle Beach to the big track, however the way everything else is configured will change.  We’ll undoubtedly switch to a left-front bind setup, but whether or not we bind both springs is yet to be seen.  With California’s surface being very bumpy and low-grip, we may opt for something similar to LOR where we have a stiffer right-front spring that will still bind at full load, but can expand and cushion the bumps and let the tires work without the suspension being too solid.  As for the rear, it’s very likely that the springs used at LOR will be used for California and changed based on what we see when it hits the track.  Our current plans are to run the same time window that we ran this week, hope to see you there!

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