The drivers are deliberately rolling over thousands of discarded pieces of tire rubber scattered outside the racing line. That rubber sticks to their hot tires, making them look rough, uneven, and covered in black chewing gum by the time they return to the pits.

Why would a driver want that?

First, What Are “Marbles”?

If you have ever heard a commentator say that a driver “went onto the marbles,” they are talking about loose pieces of rubber that have broken away from the tires.

F1 tires endure an incredible amount of punishment. During every braking zone and high-speed corner, the tire is being pressed, stretched, heated, and dragged across the asphalt.

As the cars circulate, those pieces of rubber are pushed away from the most frequently used part of the track. They accumulate along the edges of the racing line and around the outside of corners.

Some pieces are tiny flakes. Others roll together into larger, rounded clumps that resemble little black marbles—hence the name.

During the Race, Marbles Are the Enemy

Have you ever stepped onto loose gravel and felt your foot slide underneath you?

That is a rough comparison to what a driver experiences when an F1 car runs onto the marbles—only it is happening at racing speed.

A tire produces grip by pressing directly against the asphalt. The rubber interacts with the tiny peaks and valleys in the track surface, helping the car accelerate, brake, and turn.

Marbles interrupt that connection.

The loose rubber gets caught between the tire and the track, preventing the tire from making clean contact with the asphalt. Instead of gripping the circuit, the car begins sliding across a layer of rubber debris.

Drivers often describe the sensation as being similar to driving on ice.

This creates an especially frustrating problem: once a driver runs wide, it can be difficult to recover. The car encounters the marbles, loses grip and is pushed farther off line—where there is even more loose rubber. When the driver finally returns to the racing line, some of that debris may remain stuck to the tires for several corners.

This is also one reason passing around the outside becomes so difficult late in a race. The attacking driver may have to leave the grippy racing line and brake on a dirty part of the track.

For nearly the entire Grand Prix, drivers want nothing to do with the marbles. Then the checkered flag appears, and suddenly everyone goes looking for them.

Why Drivers Collect Rubber After the Race

Once the race is over, the driver no longer needs to attack every braking zone or carry maximum speed through the corners. The goal changes.

Instead of searching for the fastest path back to the pits, the driver begins searching for rubber.

The tires are still hot and slightly sticky. When the car travels through the dirty sections of the circuit, loose marbles attach themselves to their surfaces. Drivers may weave gently or place two tires outside the usual racing line to collect as much rubber as possible.

By the time the car reaches the pit lane, each tire may be coated in an irregular layer of discarded rubber.

Why a Little Extra Weight Can Matter

An F1 car must remain above a minimum legal mass. Teams do not want to make their cars unnecessarily heavy because additional weight can hurt acceleration, braking, cornering and tire performance.

The ideal car is therefore designed to operate close to the limit while maintaining a safe margin.

By the end of a race, however, the car has changed. It has consumed most of its starting fuel. Its tires have lost rubber. The brakes, floor plank and other components have experienced wear. Small pieces of bodywork may also have been damaged or lost.

Teams calculate these changes carefully, but no calculation can make physical wear disappear.

Collecting loose rubber during the cooldown lap gives the car a little more protection. Every marble stuck to the tires adds a tiny amount of mass. Across all four tires, that additional rubber can increase the car’s margin before it reaches the scales.

It is not a magic trick, and teams cannot intentionally race with an illegally light car expecting a few dirty tires to save them. But when the difference between compliance and disqualification can be extremely small, every legal bit of protection matters.

What Happens at the Post-Race Weighing?

Crossing the finish line does not immediately make the result official.

After the race, the FIA can select any classified car for weighing and technical inspection. If the driver leaves the car before it is weighed, the driver must report to the technical delegate so their weight can be measured separately and added to the car’s figure.

If the combined measurement falls below the required minimum, the car may be disqualified. One limited exception covers a shortfall caused by the accidental loss of a component.

The rules also prevent teams from simply adding something after the race. That is why the rubber pickup happens while the driver is still on the circuit—not after the car reaches the garage.

When the Lack of a Cooldown Lap Became Important

The 2024 Belgian Grand Prix showed us just how much post-race weight can matter.

George Russell crossed the finish line first after completing an unexpected one-stop strategy. It appeared to be one of the most impressive victories of the season.

Then came the post-race inspection.

Russell’s car was found to be 1.5 kilograms below the required minimum after its remaining fuel was drained. He was disqualified, and the victory passed to Lewis Hamilton.

Spa-Francorchamps has an unusual post-race layout. Rather than completing a full cooldown lap, the drivers turn into the pit lane shortly after the finish. That meant Russell did not have the normal opportunity to travel around the circuit collecting rubber.

Would collecting marbles definitely have made the car legal? We cannot say that. Tire wear, fuel use, component wear, strategy and the car’s original weight margin may all have contributed.

But the incident made one thing painfully clear: in a sport decided by thousandths of a second, a surprisingly small amount of weight can decide whether a victory remains in the record books.

Are Drivers Trying to Save the Tires?

A common theory is that drivers collect rubber to protect the tires or help engineers inspect them.

There may be secondary benefits to covering the tire’s worn surface, but that is not the main reason for the post-race weaving. Engineers already have an enormous amount of information from tire temperatures, pressures, lap times, energy loads, driver feedback and physical inspection.

The teams also do not keep race tires for unrestricted future use. The tires are controlled, tracked and eventually returned to the appointed supplier.

The main reason for deliberately picking up marbles remains the additional mass they provide before post-race checks.

Why Not Collect Rubber During the Race?

Because the possible weight benefit would be nowhere near worth the loss of grip.

During the race, collecting marbles can compromise the next corner, damage a driver’s lap time, overheat the tire surface or even send the car into a spin.

After the checkered flag, lap time no longer matters. The car is moving more slowly, and the driver can leave the racing line without sacrificing a position.

The same rubber goes from being a serious hazard to a useful tool in a matter of seconds.

The Race Isn’t Over at the Checkered Flag

This is one of those small F1 details that changes what you see once you know about it.

The next time the checkered flag falls, do not immediately look away. Watch where the drivers position their cars. Notice how they abandon the clean racing line and drift toward the dirty edges. Look at the tires when the cars arrive in parc fermé and see how rough and uneven they have become.

What once looked like a lazy cooldown lap now tells a much more interesting story.

The drivers have spent the entire race avoiding those little pieces of rubber. Now, with the racing finished, they are collecting every bit they can.

Because in F1, even after you cross the finish line, you still have to make sure the result survives the scales.