Jarno Trulli's Lotus avoids the marbles

Marbles are small pieces of rubber which are scrubbed off racing tyres in use and land on the track surface, where they accumulate off the racing line.

If a car leaves the normal line and drives over these pieces of rubber it will have much less grip than normal. The effect is like 'driving on marbles', which is where the name comes from. The rubber pieces will stick to the hot tyre surface and it may be several corners before the tyre has cleaned up sufficiently to grip properly again.

Often drivers will deliberately drive on the marbles on the slowing down lap after the end of a race, in order to pick up waste rubber on their tyres. This adds a small amount of weight to the car, which can sometimes be the difference between passing the post-race weight check and being disqualified for running under weight.