A radiator must never be emptied

"The theory is that you need a soft axle in order to ‘free’ the kart a little when there is a lot of rubber on the tarmac. However, that’s not always true, because much depends on the type of rubber used: if the tyre has a very stiff shoulder, an intermediate axle is preferable. For example, Vega 'Verdi' tyres on a very rubberised track require a neutral axle rather than a rigid or soft one... Basically, you need to look at the tyres, not whether the track is more or less rubberised!
Another important factor is chassis behaviour: a very stiff frame requires a soft axle and the opposite is true for stiff axles. However, before looking at the axle, the seat must be positioned correctly, so that the chassis is balanced. Then, you need to check the type of tyre fitted, because everything revolves around the tyre: it represents the only element standing between the kart and the track".