Following on from my initial blog about using longboard/skateboard wheels on a gravity racer, there comes the sticky subject of brakes.
Most regulations for soapbox races insist that you must at least have effective brakes that operate on two wheels on the same axle, i.e. both fronts, or both rears. Scrub brakes are often forbidden – so anything that slows you down by rubbing on the wheel and tyre, or the road surface, is not allowed.
This usually leaves you with the choice of drum or disc brakes, much like on a regular road going car. For gravity racers, disc brakes are commonly stolen from mountain bikes (hydraulic or cable operated), and drums also, with Sturmey Archer hub brakes being common – I specced these out on my initial gravity racer design, the LGR001.
With a skateboard wheel the problem is diameter. Even the very largest longboard wheels are only 100mm, and it’s almost impossible to find cheap discs that are this small. Even if you could, when dealing with a wheel that has the bearings installed in it (essentially a wheel, tyre and hub all in one) how do you attach the disc to the wheel? Looking at the electric skateboards on the market (that use belt drive) the answer seems to be to use a disc that is fixed to the inside face of the wheel using bolts. It would therefore be possible to machine a disc with a hole in it, align it on a shaft, and the screw it right into the urethane. Then, it’s a case of locating some small calipers and mounting the lot up.
Drums would be a much more tricky proposition as you’d probably have to make the whole lot, and quite frankly that’s beyond my capabilities at this stage.
The simplest solution I can see, is just to use pushbike brakes – the sort found on road bikes. These have a single mounting point at the top (unlike v-brakes that have two, and in locations that would be hard to provide) and could be set up to apply braking force to the “rim” of the longboard wheel, i.e. the flat face of the wheel before the face slopes inwards towards the bearing.
I suppose whether or not this is legal depends on the interpretation of the rules. The brake is not acting upon the road contact area of the wheel, although it is part of the same section, just “around the corner” if you will. If you think about it, it’s not really any different to using a bike wheel, where the brakes act upon the rim of the wheel rather than the tyre.
Anyway, that’s the plan for now, and if it turns out that the rules make it illegal, I’ll be looking at teeny weeny little disc brakes…