The axle is the part, rotated by the engine, transmits movement to the wheels and allows the movement of the kart. There are several types, which vary according to hardness, toughness, elasticity and yield strength of the material.
The axle is connected to the chassis through three bearings arranged asymmetrically; this "unbalancing", favoured by the asymmetry of the chassis, does not generate any problems, even if the central bearing is often released to further soften the body. Its characteristics greatly affect the performance of the kart.
A harder axle is normally used on wheeled tracks and with soft tyres, trying to achieve a set up with higher torquity rigidity. With little grip, however, it is better to use a soft chassis. The key is a very simple mechanical element that binds the axle to the hubs, gearwheel supports and disc housings.