For NASCAR Drivers, It’s Important to Lose One’s “Marbles”

Why do NASCAR drivers swerve? See why it’s advantageous for drivers to weave back and forth on a racetrack before or during a race.


Jun. 11 2022, Published 1:11 p.m. ET

During the pace laps before a NASCAR race or even during the race itself, you might notice racers weaving from side to side. So, why do NASCAR drivers swerve so much, even before the green flag?

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In a Hendrick Motorsports video from 2018, NASCAR driver Alex Bowman had a succinct explanation for the swerving drivers do during pace laps before a race restart: Swerving serves “to heat your tireand to get all the trash off of them to be ready for the restart,” he said.

Alex’s answer gets at two of the big reasons behind all the swerving. Read on for more details!

NASCAR drivers swerve to clean the “marbles” off their tires.

According to HowStuffWorks, “marbles” can be hazardous on a NASCAR track. In the world of auto racing, the term “marble” refers not to a spherical glass toy but to a bit of rubber that comes off a tire during a race. As tires go over the racetrack, the heat generated starts breaking down the elastic polymers in the tire, and the rubber that is worn away forms marbles.

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And when drivers run over these bits of rubber, their tires can lose grip on the racing surface. In fact, that’s why they’re called “marbles”: because driving over these rubber bits can be as destabilizing as stepping on those glass orbs.

Plus, tires pick up marbles through friction, as physicist Diandra Leslie-Pelecky, author of The Physics of NASCAR, explained to NBC Sports: “Rubber molecules in the tire form atomic-level bonds with rubber on the track. While ‘interatomic bonds’ sounds fancy, it’s basically like you stepping on a wad of gum during a walk. The gum bonds to the bottom of your shoe, and then either your shoe pulls away from the gum/sidewalk, or the gum pulls away from the sidewalk and sticks to your shoe.”

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Diandra went on: “This adhesive type of friction creates the gobs of rubber that build up on a tire after a run. Drivers on old tires swerve before a restart partly to scrape off the rubber gunk and expose a clean surface that will provide better friction.”

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Usually, marbles accumulate on the top “groove,” or the top edge, of a racetrack, according to HowStuffWorks. When NASCAR drivers have to drive along top groove — if, for example, they’re forced out of the “racing groove,” or the inner fast lane — they’ll likely run over many of these marbles, and they’ll have to swerve back and forth to get the rubber bits off their tires.

The swerving also heats the tires, improving traction.

Motor Racing Sports reports another reason for the swerving: Doing so keeps racer tires warm. Why should that matter? Because even though the heat from friction starts wearing down the tire, colder tires are harder for drivers to control. The colder the tire, the less grip it has with the racing surface. Drivers have compared driving on cold tires to driving on ice, per Motor Racing Sports.

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Plus, swerving helps even out the heat on the tire. According to the site, “blistering” happens when tires are hotter inside than they are outside, while “graining” happens when tires are hotter outside than they are inside. The more you know, right?

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