Expert Advice
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How to adjust a kart's set-up for rubberised tracks
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A kart is a difficult “beast” to tame and just when you think you’ve done it, everything changes and you have to start all over again. This is due to the tarmac conditions on the track, which change continuously based on temperature, amount of rubber, humidity, etc. A set-up planned “on paper” often doesn’t work in practice when there is a lot of rubber on the track. In fact, grip should not always be as high as possible, but adjusted so that it enhances performance under braking, when entering bends, over distance and provides traction exiting bends, but must not result in the kart being stuck to the tarmac. What needs to be done so that the set-up feels less bound and more suited to a very rubberised track, perhaps starting from one planned for the same track, but with less grip? We asked Rickard Kaell, the highly experienced Birel ART team manager.
Nowadays, usually, we always look for grip, because tyres are harder than in the past, both in terms of compound and carcass. Nevertheless, we should always try to free karts on very rubberised tracks compared to the set-up when there is little rubber. Clearly, the steps taken depend on several factors, as well as the set-up you start off with. At the back, I would say that the factors and the parameters to work on are: axle hardness, height, type of rear hub material, axle and hub length.
At the front end: camber, height, caster and the hub material. Lastly, of course, work needs to be done on tyre pressure.
In the past, softer axles would be used to free the rear of the kart, whereas nowadays, with the new harder tyres, from my point of view the reverse needs to be done: i.e. harder axles are used. This is also because the weight has increased weight and, on very rubberised tracks, axles that are too soft tend to flex and perform poorly. That’s why we need to use a harder axle to free the rear end. Varying the length of the axle is useful, but has less of an impact: reducing it frees the rear end further, allowing the kart to go around bends smoother. Please note: in order to achieve a noticeable effect, length has to vary by at least 2 cm on each side (4 cm in total).
Height undoubtedly has a considerable effect on the set-up. In particular, raising the rear end (which means lowering the axle with respect to the chassis), makes it easier for the inside rear wheel to lift when cornering, which is key to the kart being free on its rear tyres.
Raising of the rear end also impacts the front end, which helps to free the kart, albeit to a lesser extent. Raising the bodysheel at the rear end compared to the front end reduces the caster angle, thereby decreasing the load on the front wheels and, consequently, grip.
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