The tyres and tarmac rule refers to the stopping distance behind another vehicle when you come to a stop in traffic. Always stop so that you can see all of the tyres of the vehicle in front and around a metre of road tarmac. This may vary slightly due to the height of the driver, but provides an effective guide to go by. If you stop too close to the vehicle in front, should it roll back, it could damage the front of your car. Stopping too far behind another vehicle is also dangerous as the vehicle behind you is unlikely to be expecting you to stop that far back and will not be prepared to stop.