Why Do NASCAR Drivers Swerve and Weave Their Cars?

In all forms of motor racing, including NASCAR, you will see during the parade laps prior to the start or under caution, drivers swerving their cars around the track from side to side. Although 40 cars doing this may look a little strange there is a scientific reasons why drivers swerve and weave on a racetrack.

NASCAR drivers swerve and weave their cars during warm up laps or under caution for two main reasons. Tires need to be at high temperatures achieve optimum performance and weaving creates friction. However, once heated tires become sticky and pick up debris reducing both safety and grip. Weaving helps to remove this.

We look at the physics behind this, the timing and other motorsports that do this below.

When Do NASCARs Drivers Swerve On The Track?

NASCAR drivers tend to swerve on the laps before the races begins. These laps are known as pace laps in NASCAR, as they are completed behind the pace car. NASCAR has these laps as they use a rolling start, and the drivers choose to swerve from side to side to heat up their tires and brakes, which will allow them to nail the very important start procedure and give them the optimal chance at getting away well.

If they fail to get heat into their tires before the start, they would struggle to find any grip at the star which could result in a loss of traction that could cause a spin or crash. These incidents near the start of races, which is where the field is most bunched up, can have devastating effects in NASCAR, and they are commonly known as ‘The Big One’.

The drivers may also weave or swerve during caution periods, which are fairly common in NASCAR Cup Series races. This will allow them to get a better restart and ensure that they do not fall back instantly which could ruin their entire race. 

The drivers may also swerve to remove any debris from their tires, as well as give them a general clean to ensure that they a fit to operate at the high-performance levels that the drivers demand. This swerving to remove debris results in piles of rubber piling up on the track, sometimes known as ‘marbles’, and they accumulate on the racing line throughout the race.

Running over these marbles can make the grip of the car worsen, and so drivers swerve from side to side to get rid of them.

Why Do NASCAR Drivers Swerve and Weave on the Track?

One reason why the drivers swerve is to keep their tires warm and within the optimum operating window. When not travelling at the very fast speeds of green flag running, the tires can lose temperate very quickly if they are not managed.

This rapid reduction in temperature would also result in a rapid reduction in grip, which would make the car harder to drive and slow the driver down. This is all down to the friction grip that the tires have with the circuit.

The hotter the tires get, the stronger the friction is, and the cars get faster as the tires are less slippery. Cold tires can be so hard to use that some drivers have compared it to driving on ice, which is near enough impossible. It is also essential to ensure that the heat on the tire is evenly distributed, and weaving can help to do this.

If the tires are hotter on the inside than the outside, a phenomenon called blistering occurs, which can wear the tires down more quickly, and make them less effective. A similar effect, known as graining, occurs when the outside of the tire is warmer than the inside.

Marbles on a Slick racing tire

What are Marbles on a Race Track?

You will have seen, numerous times, NASCAR drivers coming into the for a pit stop and having tires changed. This is due to wear on them while racing around. The tires shed rubber and unless the track is a road track like the Circuit of Americas or the Glen, then this rubber from the tires has no wear to go on the ovals tracks. It comes off the tires and stays on the track, often higher up off the racing line.

These small pieces of rubber are called marbles, and the area of track they accumulate on is called the dirty section. On older rougher tracks this can build up significantly during a long NASCAR raceOpens in a new tab.. They also keep their heat and when they come into contact with a car tire will stick to it.

The image above and below shows you what these marbles and debris look like when stuck to a racing tire.

This will create areas of uneven grip, where only some of the racing surface of the tire is in contact with the road.  This is very undesirable when moving at 200 miles an hour! As it affects the steering and grip on a car already operating at the very edge of its performance.

So weaving is also used to remove and distributed any marbles that have built up on the tires. Some drivers will also weave to test the grip level of the circuit before a start or restart to ensure that they adapt to the track very quickly.

Some tracks are harder on the tires than others, with indianapolis Opens in a new tab.being know for being hard on tires.

Other Motorsports Also Swerve at Low Speeds.

Swerving to heat tires is not found solely in NASCAR. even with the tire warmers utilized in Formula 1 you will still see F1 cars weaving around the track to keep or increase the heat in the tires. In fact most motorsports try to get as much heat ( within reason of course) into the tires during slowdowns and cautions.

Even in World Rally Championships drivers will use asphalt areas before the start to try to get some heat into the tires Opens in a new tab.before they race.

Does NASCAR use Tire Blankets?

Tire blankets, which are also known as tire warmers, are devices that help to keep the tires warm before a race. They are used by Formula One teams to ensure that the tires are very hot when they go onto the car before a race start or during a pit stop.

The system used in F1 has a blanket that contains wires. They have a control box that allows a technician to decide the temperature. Energy then flows through the wires which are in the blanket, which is also very heat conductive. This allows the heat of the tires to rise by over 100 degrees. However, these tire warmers are banned and not used within NASCAR.

This is due to the fact that NASCAR wants the teams to be on equal footing during the races. They also want the teams to use the tires as they come, which are provided by Goodyear. The tire warmers are artificial, and they could give one team or driver an advantage.

The tire warmers are also banned in all of the other major US racing series. This means that the drivers have to weave to build up heat in the tires, which begins at a very low level.

Why Do NASCAR Drivers Swerve and Weave During A Race?

How Hot Do NASCAR Tires Get During a Race?

NASCAR tires reach very high temperatures during races, and to ensure that they can run with these extreme heats, the tires are filled with nitrogen rather than standard air. This is due to the fact that nitrogen is a more stable gas than standard air.

Standard air contains moisture, which nitrogen doesn’t. When temperatures are high, the moisture evaporates to become a gas which adds more pressure to the tires. This means that nitrogen is more predictable for the engineers, as it is dry and does not contribute any extra pressure change when the temperature is increased.

It is very important to keep the tires stable, as during the races they can hit temperatures of over 200 degrees Fahrenheit. The engineers can measure where the tire is hottest straight after a race by using a temperature gauge in the left, right and centre of the tire.

They can then analyse where the tire is the hottest, and what has to be done to address it. The measurements will also allow the teams to check if the tires have the correct level of primary camber, and well as see if they are inflated properly.

In an ideal world, the cars would have tires that have identical temperatures all over, but this is very difficult to achieve in real life. Weaving on the track helps to improve the heat balance and get the tires ready for racing.

Final Thoughts

So despite look a little strange watching 40 cars turning side to side like a drunk snake there are perfectly valid reasons why this happens. The four tires are one of the most vital elements of any race car and keeping them both in the best condition possible, and as much of them on the track as possible, is not just good racing practice it’s safer racing practice as well.






Al lifelong Motor Racing Fan, with a particular love of NASCAR and IndyCar racing. Been in and out of cars of varying speeds since i was a child and sharing what i have learnt here.

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