Behind a tractor all sorts of agricultural implements or wagons may be attached. The coupling should be lower than the rear axle. If not, there is a risk that the tractor skips when the cart gets stuck. Many farmers however, take the risk and opt for a higher coupling, because this generates more tractive power. Vehicles are sometimes connected slightly besides the tractor, in order to protect the soil from too much compression, but the wheel pressure may also be reduced by a 'twinned' pair of rear tires, so the tractor gets more grip and will subside less quickly . Nowadays extra wide tires are used, even to a meter wide, to reduce the pressure. More pressure means deeper tracks and damage to the soil structure or to the crop, which should be avoided as much as possible.