Part of the excitement of a NASCAR race is seeing how the pit crew completely rejuvenates a car in around 10 seconds. A driver pulls in, and seconds later, he is rolling out of pit stop road, accelerating to eat more miles in the long-lasting endurance races.
Over as quickly as it started, the magic that a pit crew performs needs to be slowed down to be appreciated.
- During NASCAR races, mechanics replace tires in about 10 seconds and must be precise to prevent cross-threading of the lug nuts.
- Pit crews avoid cross-threading by using drift punches or dowel pins with special lengths of unthreaded bolts that fit accurately over the nuts.
- Ensuring axis of rotation alignment, cleaning wheel studs and hardware, and using torque wrenches and wire brushes are some methods mechanics use to ensure proper tire installation.
Several race-critical operations are performed in the 10 seconds a race car sits in the pit. One of the most important is that fresh tires are put on every time the driver stops. Tires take the brunt of the race damage, and a fresh set improves everything from top speed to handling.
This means a pit crew needs to do everything perfectly and can never, ever cross-thread when tightening a tire with a lug nut; here’s how they avoid doing that.
What Does Cross-Threaded Mean in NASCAR?
When the thread of a nut doesn’t sit right on a bolt, it can be considered cross-threading. The obvious sign is that a lug nut becomes impossible to tighten and may even be hard to remove. If this were to happen during a race and the point crew was unable to remove a cross-threaded bolt, precious time would be lost, and the driver would be thoroughly annoyed.
Think about when you are screwing something onto a threaded attachment, whether a water bottle lid or a fastener of some sort. If you don’t line up the threads correctly, then the larger attachment will sit crooked and not tighten to form the tight seal that is desired.
NASCAR mechanics have developed ways to avoid cross-threading during pit stops and are able to replace tires in a blink of an eye without causing any severe damage to any wheel components.
How Does a Pit Crew Not Strip Lug Nuts?
It can be extremely difficult trying to tighten something that uses threads quickly, and getting the position wrong as you tighten is a recipe for disaster. Fortunately, the lug nuts NASCAR vehicles use are designed to make cross-striping impossible with the length of unthreaded bolt that extrudes far enough for the nut to sit tightly on the perfect thread match.
Pit crew mechanics need to place the nuts on the bolts in the proper alignment before tightening, and a drift punch or dowel pins can be used to properly position the nuts. This takes some pressure off of the mechanic to move accurately and rapidly and makes sure the tires are secured properly before the driver leaves the pit stop.
Improperly secured lug nuts can turn into missiles during a race causing serious damage to other vehicles and even possible injury to fans.
The bolts slip over the nuts and are easy to tighten since they drop down an unthreaded top that brings the bolt to the thread and lines it up perfectly. The nuts will rest against the tire and can be tightened with the standard impact driver pit crews use. To make the task easier for rear tire changers, the endurance team uses an impact gun with the proper torque set and the correct fitting for the lug nuts bolt diameter.
Preparing the torque wrench and other tools in this manner reduces the time it takes the race team to slap a new tire on the wheel stud, line it up, tightened it, and move on to the other tasks a driver needs.
Reasons for Cross-Threading
The axis of rotation needs to line up perfectly for the lug nuts to tighten the tires to the wheels. If there are any issues with the hardware or the studs on the wheel are dirty, then it can be difficult for mechanics to do the job quickly and correctly.
Some issues like mismatched threads can be fixed prerace with a thread file or other special tools, but make sure not to remove any of the 5 threads, or you will face NASCAR violations. In a pinch, a wire brush can quickly clean the wheel and tire parts giving pit crews a better idea of the work that need to be done and an easier time properly securing the bolts.
Below are other reasons for potential cross-threading and how race teams prevent them.
|Nut Placed at Wrong Angle||A new nut creates threads that run against the existing threads preventing the bolt from securing the tire tightly||Nuts fall down a non-threaded section of bolt that lines the threads up perfectly, preventing this kind of cross threading|
|Mismatched Pieces||The threads do not line up correctly, and tightening results in new threads being carved in and severe damage to the bolt||Use parts that were machined together, preferably from the same batch, to avoid slight adjustments in miter alignment between boxes of lug nuts|
|Dirt and Debris||Dirt or grime on a bolt can stick to the threads preventing a nut from tightening and forcing the threads out of alignment||Use a wire brush or grease-cutting wipes to make it easy for nuts to tighten on bolts correctly|
|Strong impact or Abrasion||A bang during the race can knock bolts out of alignment or bend the threads; the same can occur from a large groove or cut from a mid-race collision||Replace damaged parts quickly or adjust force and angle to compensate for damage if the replacement during the race is not possible|
How Do NASCAR Mechanics Control Torque?
Over-torque and under-torque in NASCAR are serious mistakes for driver mechanics to make. There are a few ways that pit crews deliver the exact amount of torque needed to the lugnuts while under tremendous time constraints to not mess up or take too long.
Some torque control is the result of the materials NASCAR vehicles are put together with, but the right tools and the correcting training in setting and tightening the bolts is also critical for the safe and rapid tire-changing routine a winning race team needs.
Strong Car Parts
Softer aluminum wheels, although lighter, would never be able to handle the rigors of a 500-mile race, making an aluminum wheel useless for attaching high-grade bullnose wheel studs. Instead, NASCAR teams use 15-inch steel wheels designed for the smooth ovals and custom wheels cars have.
The current studs are attached with lug nuts that work as essentially wedges to secure the wheel tightly during a pit stop wheel swap.
Calibrated torque wrench or impact driver set to a specified torque. The compressed air is at a set psi, so if the tool is correctly tuned, the mechanic will hear drumming when the correct torque sticks the lug nut to the fresh tire. A wire brush and rags with non-slip solvents can help clean the area making lug nut adjustments and tightening much easier during a tire swap.
Specially Designed Hardware
The lug nuts that NASCAR uses are designed to make cross-threading and applying too much torque to the point of damaging hardware or car parts extremely unlikely. The shape of the lug nut has a nonthreaded shoot that the mechanic’s gloved hand can easily drop a nut over, which falls perfectly in line with the thread.
Once the bolt is tightened, the seal is secured, and the tire will rotate smoothly with no vibrations or extra noise.
How Many Tire Changes Occur in a NASCAR Race?
Tires are frequently changed during a race, and the tire changer is one of the most important members of the pit crew. The time in a pit is dependent on the tire change, as all other aspects take far fewer seconds. A slow tire changer can lose a race which typically comes down to the blink of an eye anyway.
A tire changer should be prepared to work hard, especially on the longer tracks with many miles of total race distance.
It is common for a racer to need adjustments anywhere from 4 to a dozen times in a race leading them to pull off into the pit stop. Depending on the length of the track and the total miles of the race, a driver will change their tires at each of these stops, which means it is possible for a driver to go through almost 50 tires a race.
Not every tire needs to be changed in every pit stop as rear tires are where the force is generated and burn off most rubber, as well as the tires that lead the drift around turns.
Previously all NASCAR series used 5 lug nuts with glue to secure the tires to the wheels. This meant a tire changer had to remove 5 nuts and replace and perfectly tighten five lugs every time a tire was changed for each tire. NextGEN race cars only utilize 1 center lug nut cutting the time needed to change and the amount of work and parts to keep track of down drastically.
According to race teams, a single lug nut is much larger than the traditional 5 lug nuts and takes .5 seconds to remove vs. the .8 needed to take off all 5 nuts. This savings in time can translate to drivers back actively racing faster and reduces the strain on the crew.
The traditional 5-lug nut system is still used on cars in the other series of NASCAR and will continue to do so for a long time. NASCAR’s main series continues to push the boundaries of race performance and safety while staying true to the street car brand that stock car racing clings to. This change in the lug nut system aids in faster racing, less off-track time, and technological improvements that make it even easier for NASCAR lug nuts to not cross-thread.