Prototype FOX RAD DH Shock

Last year's World Championships in Pietermaritzburg, South Africa, saw all sorts of prototype equipment designed to give racers the edge on the big day, a lot of which will eventually become production parts that you'll be able to purchase, as well as a few items that won't ever be available to anyone not on a factory race bike. Pinkbike gave you the first and only in-depth look at FOX's prototype RAD DH shock from that weekend, and at the time it looked as if the very special damper might never be made available for purchase. In fact, prodding FOX late last year on the same subject saw us get the silent treatment, with them not willing to comment on the shock's future. Fast forward to last weekend's New Zealand National Championships where Trek World Racing's Brook Macdonald had his prototype 650B Session fitted with what appears to be an evolved version of the same shock we spotted at last year's World Champs event. What does it mean? This latest version is much more polished and appears to be pretty close to consumer ready, which are both not so subtle hints that it will eventually reach production.


This new model of the RAD shock features a much more refined body compared to the earlier version (pictured below), with rounder edges and unnecessary aluminum removed from the upper shock end, bridge assembly, and the piggyback. The radically different size of that last component is most obvious, though, as it's quite a bit shorter than what we saw last year. The job of a shock's piggyback, and the internal floating piston (IFP) that is usually inside of it, is to compensate for oil displacement caused by the shaft entering the shock under compression, while also allowing for more damping oil to be used compared to an inline shock in order to fight heat build-up. The position of the IFP within the piggyback and the pressure behind it can also be used to tune the amount of ramp-up in the shock's stroke, although this needs to be balanced properly with the amount of oil volume displaced by the damper shaft when it's compressed into the body. With that in mind, FOX may have learned through testing the RAD shock on different downhill bikes that the longer piggyback simply wasn't needed, and that adjusting the height of the IFP ever so slightly within a shortened version of it was enough to compensate for different stroke lengths that they might produce. After all, they're not going to manufacture different piggybacks for different length shocks.



The other obvious difference between the earlier prototype and the version on Brook's bike is the shape of the adjustment dials. Just as we speculated last year, it does offer both low-speed and high-speed compression and rebound adjustments, each done separately, but it takes a second look at this latest version to see exactly how that is accomplished. It appears as though the blue (compression) and red (rebound) anodized components are actually caps that are threaded into place at the factory, while damper adjustments are made with hex wrenches at its center: high-speed damper adjustments are done with a 6mm hex key, and low-speed with a 3mm hex key concentrically and deeper inside. The pin spanner holes on both of the blue and red caps might actually allow easy access to the compression and rebound circuits, and unthreading them from the bridge could give mechanics or racers the ability to make quick changes to the damper circuits that go beyond what would be possible by turning the adjusters. This is, of course, all speculation at this point, and the pin spanner holes could only be there for testing purposes and might not be present on the production version. The stacked arrangement of the dials also makes the most of the limited real estate available on the piggyback bridge, and means that the shock should be compatible with pretty much every downhill bike on the market.