Commodore’s Garage #34 – Truck Project: Auto Club Speedway

Somebody needs to mark the calendar because a sign of End Times arrived last night after our Truck race:  Somebody was happy with the way Jeff Parker raced him.

All jokes aside, it’s safe to say that our race at Auto Club Speedway was a one-and-done situation because it’s highly unlikely that we’ll be able to equal the result we had in any subsequent race.  Consider the situation:  The race had a 3822 SOF, was populated with the names we’re used to racing against in the Class B Series and who have run the truck a lot more than we have, and we hadn’t raced any trucks on a track larger than a mile since mid-2016.  We started 20^th, 22^nd, and 24^th but finished 4^th, 5^th, and 9^th.  Yours truly was bringing up the rear again, but I have a very good reason for this which we’ll address later.

As I’ve mentioned in previous Garage articles, the three of us have never been able to run the same exact setup.  So, following the race at Indianapolis, we each went our own way with the California setup but didn’t wind up straying too far from each other.  As a matter of fact, we were all within a tenth of each other in practice so that’s pretty impressive in my opinion.  We’re going to focus on my setup alone, however, but I will point out a few points where I know my teammates’ setups varied.

Setup Background

California is our first Intermediate track of the year, so the setup needed to be more heavily focused on the aerodynamic aspect instead of mechanical grip like we did at Indianapolis and Myrtle Beach.  This means the heights were much more crucial and keeping those heights from changing a lot in the corner is vital.  At Indianapolis we could sacrifice a bit on the body attitude for the sake of keeping the tires in contact with the track (this is why we spent so much time curing the bounce), but not here at California when we’re over 180mph!

Despite the shift in thinking behind the setup, it wasn’t dramatically different from the IRP setup.  The big right-rear spring stayed, the rear spring split almost went unchanged (ran a little softer at California to help rotation past center), the track bar was still right-side-high for extra skew, and one of the front springs was bound while the other was not.  The major difference, however, was which spring was bound:  on my car, I bound the left-front to put a hard-stop on the left-front height just to make it easier to control the splitter’s height, something that was a bit of challenge at Indianapolis last week.  Alex went the opposite way with his setup, basically running the same springs reversed so that his right-front spring bound and the left-front wasn’t.  This isn’t particularly surprising, since we did the exact same swap in the Xfinity cars at California in 2016.  Just like in the 2016 race, he and I eventually raced around each other for a decent portion of the race.  Fine-tuning the right-front travel was fairly simple using the sway bar diameter since it was behaving as a torsion spring.  Again, asymmetry was used to flatten the splitter attitude and the bar was lightly preloaded.

Crossweight Adjustment & LF Spring Rate

The setup was largely plug-and-play for California.  Once the heights were set where I wanted them, it was basically an exercise in crossweight adjustment to get the balance right.  This wasn’t quite as simple as it was in the previous weeks and I wanted to dedicate part of the article to making this change with a front-end setup like I was running.  If you haven’t seen the quick-and-easy way to make crossweight changes in the video I posted last week, head over to our Facebook page so you know how everything should work.

For aerodynamics, the left-front corner is extremely crucial to the car’s performance.  If it gets too high there will be a lot of drag and a major loss in downforce, so keeping it from moving around during the setup process is very important.  For a coil-bind car like I had, the left-front spring is serving as a “hard-stop” for the left-front corner.  Whenever I made a crossweight change to the truck the available travel in the left-front spring also changed:  travel is reduced when crossweight was lowered, travel is increased when crossweight was raised.  The same (but opposite) is true for the right-front spring, so it’s important to know this is going on when you make a crossweight change.

I got around this by increasing the left-front spring rate by 10 lb/in every time the available travel started to decrease enough to raise the left-front corner when the spring was bound.  This is something you can see in telemetry by overlaying two runs together, and simply increasing the spring rate when the splitter gets too high.  This is a little counter-intuitive since it would make more sense to run a softer spring rate to allow the car to drop, right?  Well things get a little funky when we’re binding springs, so the way springs are designed has to be considered in this situation.  As a spring increases in rate it will typically have fewer coils in the spring, and fewer coils in a spring means more travel so whenever we have a spring completely bound like I did at California, what matters the most is how tall the spring is when it’s bound (known as “block height”).  When the spring is binding with the front end too high, we need a spring with a shorter block height, so we need a higher-rate spring which will have more travel.

For a setup like Alex’s, with the right-front bound, you would do the opposite for a decrease in crossweight adjustment.  Lower crossweight would put less preload on the right-front spring and cause it to bind later, possibly causing the chassis to hit the track.  For this case, you would need to decrease the rate to raise the front end from the track.

The Gripfest 500

Our race was not immune from whatever is causing the Truck races to be run in extremely cold temperatures.  We tested in 70°F weather and our race info page said 70°F as well, but we were about a second faster than testing.  It wasn’t until the results page was finalized that we saw the weather was actually 45°F!  Incredibly, this is not the coldest race I’ve seen this week.

With temperatures that low, we knew the racing was going to be extremely fast, and the majority of the opening laps for a tire run were wide-open if you wanted to be competitive.  While Alex decided he was going to jump right in head-first from lap 1, Jeff and I decided to lay back from the field and give ourselves plenty of room to avoid the massive crashes that ensued in the first half of the race.  It worked quite well since we had quite a lot of room to slow down and let the wrecks happen before we even got close to them, but the downside to this was that we didn’t know how the trucks were going to handle when pushed harder to be competitive.

Jeff and I decided to join in the fun later in the race past halfway and quickly discovered that our setups were just fine.  I managed to get past Alex on a restart and successfully annoyed him for much longer than I expected without losing time on the lead pack.  The three of us simply bided our time and let everyone else run their tires off before making passes and working up to our eventual finishing positions.  Jeff was quite aggressive and found his way up front, but Alex was likely kept from a better finishing position by my stubbornness.  Eventually Alex did get around me when I parked myself in a remarkably bad position that he and one other driver capitalized on.  Once we were settled in, the field formed a line and we hugged the apron like a low-banked superspeedway.

The balance was quite good and didn’t change throughout the final run when it was driven the hardest.  Checking the tires after the race, there isn’t much that didn’t go wrong on the setup at all:

Click for larger image!

If anything, the setup still has just a little too much crossweight (evidenced by the pressure buildup and temperature averages) but it’s not something to be worried about with California’s bumps and low-grip surface.  Plus, the track was 25° colder than we practiced in so having the setup show a little tight isn’t surprising.  Had I made a more aggressive run early in the race, I would have been able to decrease the right-front pressure by 1psi and the left-rear by 0.5psi, giving a much more balanced pressure buildup on the car and possibly giving me enough grip to make some passes late in the race.  Still, it’s not bad at all.

One thing that could be changed is how much load is on the right-rear.  It does show a little cool, the only tire not in the 230s across the two inside zones.  This would be a simple change by just reducing the right-rear spring rate.  I know Alex ran a softer right-rear spring than I did and his tires showed a much better right-rear temperature.  I’ll look to drop the rate at Michigan to try to balance the temperatures out a little better.

Milwaukee

Next week we’ll go back to the short-track program at Milwaukee but, instead of taking the super-short setup that was used at Indianapolis and Myrtle Beach, we’ll be unloading with something closer to California.  The long straights and higher-speeds at Milwaukee will bring aerodynamics into play, so that needs to be a priority.  It will mostly be a fact-finding mission for Iowa, since those two tracks will have very similar speeds and loads.  Again, we’ll be planning on the 9:45pm race on Thursday just to keep things consistent.

As with Indianapolis, I’ve posted the California setup I used in the race on the Commodore’s Garage Facebook page so go check it out if you’re interested!  Also drop us a like and follow the page so you can always be kept up-to-date with the Truck Project.  Take care!

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To keep up to date with The Commodore’s Garage, return to Sim Racing News every other Friday afternoon and “Like” our page at https://www.facebook.com/CommodoresGarage

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