Motor vehicle tyre. This consists of a tread of rubber that grips the road surface. The tread has markings carved into it to help generate the grip. The tread covers several other layers, including an inflated inner tube that supports the weight of the vehicle. The whole tyre fits onto the rim of the hub, the part of the wheel that is connected to the motor vehicle axle. The turning of the axle, due to the engine, causes the wheel to turn as the vehicle moves. Nuts and bolts are used to attach the hub to the vehicle, though this area is sometimes covered by a hubcap.