How Suspension Design Gave Denny Hamlin a NASCAR Race in the Pits

By | April 1, 2024

How Suspension Droop Decided a NASCAR RaceAlex Slitz – Getty Images

It appeared Denny Hamlin was on his way to a third-place finish with two laps remaining in the Toyota Owners 400 NASCAR race at Richmond until a spinning car pulled a caution flag and sent the race into overtime. Hamlin went to the pits for new tires and his crew was able to put him up front and take over a second ahead of the front runners before that final restart. It all came down to a single tire on a single corner of the car.

Pit stops in the NASCAR Cup Series have become incredibly fast since switching to single-lug wheels. It is not unusual now to see four tire changes in a matter of seconds. Joe Gibbs Racing’s No. 11 pit crew working with Denny Hamlin has become the dominant pit crew this season and all but one of its pit stops last night were in those single digits. The unspoken variable here is that each race track uses a different suspension setup than the cars. This means that the tires come off and are put on the car differently from week to week.

An optimal suspension setup for Richmond Raceway will often result in a left rear corner without much droop. This means that when the car is jacked up in the air, the wheel doesn’t drop down very far because everything is configured so tightly. This can result in the tire being very close to the edge of the fender and means that tire changers and conveyors must be very precise when changing.

nascar cup series toyota owners 400nascar cup series toyota owners 400

Jonathan Bachman – Getty Images

The left rear tire ultimately appears to have made the difference during that final pit stop, with Denny Hamlin and Martin Truex Jr. swapped positions in the pit lane as Hamlin took the lead for that final restart. Hamlin’s crew was able to make another successful pit stop, which saw them change four tires in 8.99 seconds, while the No. 19 crew of Martin Truex Jr. was more than a second behind with a time of 10.29 seconds for their four tire changes.

Let’s look at that pit stop.

In the video above, we see pit crew #19 moving quickly on the right side of the car. As they move to the left side, we see a delay in the back left. This is where that limited droop comes into play and makes the left rear tire harder to pull. That delay quickly compounds: the jack handler is late installing that tire, which results in the front tire changer turning to lower the jack instead of the jack handler, which deviates from the crew’s standard pit stop process.

The overall slowdown is almost hard to capture in the video, as it seems quite insignificant. The car takes off pretty quickly, but the margins in the NASCAR Cup Series are now so small that every tenth matters. The pit crew of Bubba Wallace’s No. 23 showed one of the worst-case scenarios of this situation. They had similar delays on the left rear, but the problems were made worse when the front changer dropped the jack before the rear changer finished attaching the rear tire. They had to jack it up again to tighten it further, which resulted in a pit stop of almost 13 seconds.

rear damper mountingsrear damper mountings

NASCAR

This is an interesting thematic intersection of pit stops and suspension design, race strategy from an engineering perspective and race strategy from a pit crew perspective. To get a sense of it, we need to understand how NASCAR regulates the suspension and how teams adjust it.

NASCAR Cup cars use an independent rear suspension that is tightly controlled by NASCAR. Where teams do have options is in how to set their dampers, along with the choice of springs. Teams will use that adaptability to adjust the car’s balance for specific tracks. In addition to how they set up the car prior to a race, the rear dampers also feature weight jackers. These can be adjusted during the race itself by a pit crew member reaching through the rear window with an adjustment wrench. The rear stabilizer bars also have adjustable blades that can be rotated to shift the balance of the car.

Nascar next-gen damper constructionNascar next-gen damper construction

NASCAR

As last night’s race started in damp conditions on wet weather tyres, this meant that teams had to make adjustments to their cars as the track dried out and they switched to slicks. This can result in things like the position of that rear wheel changing slightly as adjustments are made and crew members having to adjust in how they pull the wheel off and install the new one. The fact that crew members can quickly adapt to such changing conditions can make all the difference in giving your driver the best chance of being the first out of the pit lane. In the case of the pit stops last night, the No. 19 crew had a problem there at the rear left because the suspension was so tight against the car, while the No. 11 crew was able to adapt a little better and drive faster. that corner to get that second-place finish on the No. 19 crew and send Hamlin out first.

Nascar next-gen rear drop chainNascar next-gen rear drop chain

NASCAR

Certain tracks can also have the opposite effect on the droop and the tire can fall too low off the car when it is jacked up. In those cases, NASCAR allows teams to add a chain to the suspension to keep the tire at a certain height for those pit stops, as seen in the illustration above. Most pit crews do a walkthrough with their engineers or crew chief in the shop before a race weekend and measure exactly how far each tire drops so they can have a reference point for the race. Often they will take additional measurements on the morning of race day in case things change due to on-track adjustments.

While NASCAR pit stops may seem like a lot of speed and brute force, sometimes it all comes down to the little details. The position of a rear shock or spring can easily affect whether a tire is removed or installed quickly enough to lead to a race victory.

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