NASCAR drivers warm-up racing tires with swerving similar to Athletics warm-up.
Racing tires are different from street tires. They use nitrogen instead of oxygen to inflate and wear out quickly.
Cold racing tires have less traction and skid easily at a higher speed. Managing tire wear is one of the ways a NASCAR driver can win the race.
Why Do NASCAR Drivers Swerve Before The Race
NASCAR drivers swerve the car to warm up the tires and adjust to the track. Tires are designed for specific NASCAR tracks with varying durability and traction. So, drivers swerve to get a grip of the tires on the track. Fresh tires also need to react with heat wear off the excess rubbers (or marble in NASCAR terms).
Source: peakpx.com
The downside is that racing tires wear-out much more quickly than normal tires, and they will lack this stickiness and grip before they are warm-up to racing temperatures. So, swerving back and forth is a way to quickly add heat to the tires via surface friction.
Friction and heat is the main reason for tire wear. When heat is added to a tire, the tire vulcanizes or cures. Some tires are cured longer than others, depending on the amount of heat the track will put into a tire. Since heat changes the chemical properties of the elastomers, the molecules change their orientation.
So swerving back and forth helps clean off the rubber too.
Swerving side to side warms up the tires and brakes for optimal performance at the start of the race. Cold tires and brakes are a good recipe for crashing or at least getting passed.
Swerving During Caution
Caution is common in NASCAR, intentional or unintentional depending on a judgment call by NASCAR. ESPN reports that Bubba Wallace was fined $50,000 and docked 50 points in 2019, a day after telling an NBC Sports reporter his spin at Texas Motor Speedway was deliberate (to cause a caution) and that other drivers do it all the time.
Why Do Nascar Drivers Swerve During Caution
Besides keeping the tires warm, clearing debris is another reason for swerving especially under caution when sufficient rubber debris has collected on the race track. Hot, sticky tires pick up dirt and debris they run over like duct tape picking up lint. Drivers drive side to side in an attempt to scrub off as much debris as possible before the race resumes at high speeds.
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One might think that rubber on rubber would be a good thing since more rubber means more traction. That is incorrect thinking as Goodyear Racing Eagles, tires used exclusively in NASCAR's three series, are extremely sensitive and unsurprisingly lose grip when the tires are not in direct contact with asphalt or concrete.
Remember the only components that interact with the race track are the racing tires of race cars.