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For anyone interested I found this intresting explanation:
Rear Wheel Hubs - As a tuning device on a kart, hubs can change the kart a little or a lot depending on the track conditions and chassis type. The typical rule of thumb is a longer hub is more grip. The hub stiffens the axle underneath it so the longer the hub the more this affects the axles ability to increase grip. It’s like putting in a stiffer axle to a small degree.
Like many things in karting these days it kind of depends on the kart and the class if the longer hub adds grip to the kart. In the classes that use the 30mm and 40mm axles typically the longer the hub the more grip the kart produces. Usually in the lower horsepower classes you are trying to take as much of the grip out of the kart that you can but when the track is green, you're running a harder tire or you are running a faster class like Mini Rok or Mini Max, a longer hub can be a good way to put more rear grip in the kart.
My experience in the 50mm axle classes is a little bit different. I find hub length changes affect the kart very little. If I feel that I need to make a hub change I am usually better off to change the entire axle or cut the axle. I think the diameter of the axle really neutralizes the affect the hub has on the kart. When we were running 40mm axles in the Yamaha classes, hub length was a noticeable change but these days I rarely mess with the hub length in the 50mm classes. I usually run a medium length hub and tune around it.
A better option if you are looking to change the karts setup more drastically than the hub is to cut a little bit off the end of the axle. Between 5mm and 10mm per side. Cutting the axle makes the hubs (assuming you keep the rear width the same) action on the axle much different. Now the hub is more effective because it doesn’t have as much axle underneath it dampening its effects and the hub has more leverage on the axle. Think of it as pushing on something with 4 fingers and then only using 1 finger, you concentrate the same amount of force onto a much smaller area. A cut axle can help the kart transfer better and free up the rear of the kart, especially in high grip situations. You can also just cut one side of the axle instead of both sides if you are only trying to fix the kart in a particular corner or corners that are the same direction. Some manufacturers offer axles in different lengths so you don’t have to cut the axle, you can just put in a shorter one.
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Axle width/length Question by 'orton1966' (21 Jul 2016 @ 16:32)
