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The axle is the tube that connects a kart’s rear wheels. On the paper, this definition is correct. In reality, it is definitely reductive. Since karts are one of the few types of vehicles that do not have suspension, the axle acts as a cushion, even if, obviously, it has a very different reaction to a car’s suspension. To better understand what kind of axle to choose, when to replace it and why, what reactions you should expect ... we asked Cash Van Belle for help. He is a team manager for the IPKarting Racing Teams: Praga Karts, Formula K and OK1.
If there is a lot of rubber on the track, it is generally better to choose a rigid axle, because it frees the chassis and therefore improves performance on the bends. With a rubberized track, a rigid axle decreases the grip and helps to more effectively unload engine power when coming out of a bend, a key factor especially in single-gear classes.
If, on the other hand, there is little grip on the track, a more flexible axle is needed. In fact, this allows the rubber to work more in your favour, since it gives more grip on the asphalt.
If the axle generates too much grip, the effects on driving can be an increase in understeering when coming onto a bend: the rear pushes too much, creating a negative effect on the front and, therefore, on the direction of the kart. This problem can be mitigated by mounting an axle that frees the rear.
If, on the other hand, there is a situation where the kart jumps during braking, this is a clear symptom that the rear is too rigid; the axle does not absorb the stresses of the chassis and, in fact, transmits them to the tyres. In this case a softer axle will help the rear to act as a cushion, making the chassis work properly, thereby eliminating the jumps.
Yes, right! The tyres that need to be checked are, of course, the rear ones; although it should always be remembered that there are many adjustments that affect the wear of tyres and, therefore, more than just the axle, the entire set-up should be taken into consideration.
In any case, when the kart is stationary, if you look at the tyres with a freer axle, you will find that they are rougher to the touch and dry.
Conversely, when the rubber appears visually wet, with the tread a darker colour, this means that the grip is correct and you have basically selected the correct axle.