Riding FOX's Prototype RAD 34 Fork

FOX's Racing Application Development program (RAD for short) has been responsible for a number of advancements throughout their product lineup, all of which have their origins between the tape and under some of the world's fastest racers. And while the three letter acronym only began to be applied in late 2011, many of their products from previous years can be credited to the same development and testing strategy that has been laid out to deliver the best possible suspension to their sponsored athletes. ''The purpose of the Racing Applications Development program is to give our elite athletes an advantage through products and technologies,'' Mark Fitzsimmons, FOX's Race Program Manager, explained to us. This means that their racers are often on prototype versions of shocks and forks that may one day turn into production units - the FOX 40 is a good example of this - or might never see the light of day. Take the inverted FOX downhill fork that Gee Atherton tested awhile back, a prototype that was constructed to see if they could assemble an inverted chassis that would offer enough torsional rigidity for a pro-level downhill racer. While the fork garnered an incredible amount of attention, the project was eventually scrapped when it became clear that the fork's weight would balloon too high due to the added material required to achieve their stiffness goals.


That same development approach is being applied to the FOX 34 RAD fork that we spent a day testing on Sedona, Arizona's rough and rocky trails, and the fork on the front of our Specialized Enduro is in fact pretty much the same model that Aaron Gwin used to win the Sea Otter downhill, and that BMC enduro racer Aaron Bradford uses on the front of his 150mm travel Trailfox TF01. While the RAD 34 is likely going to offer some advantages to a top tier racer, it is a reasonable question to ask if such a fork makes sense for the average rider. ''A lot of what we learn through the RAD program is considered for production, but many times what an elite World Cup racer wants is not necessarily what a consumer wants, or even what an elite racer would want to ride on a regular basis,'' Fitzsimmons explained to us. ''With the 34, it is a combination of both. Right now we are learning what our top enduro racers need, and in doing so we are developing new damping tunes, lower friction seals, etc. Eventually, what we learn will be considered for production forks.'' FOX's 2014 forks are a good example of such development work, and Fitzsimmons also told us that there is a good chance that certain RAD-level products might be available as aftermarket upgrades in the near future. While FOX was a little vague on what exactly that may encompass, it might mean that one could purchase anything from the lightweight, anodized gold 'Kabolt' thru-axle to possibly even a full-on RAD damper cartridge.




What Makes a RAD Fork RAD?

With only a set of red and white RAD stickers on the fork's lowers that hint at it being something special, the 150mm travel RAD 34 shown here may not look like anything out of the ordinary. In fact, the fork's CSU, Kashima coated stanchions, and magnesium lowers are all straight off of the production line, while its anodized gold axle is most certainly not. The 15mm thru-axle, dubbed the 'Kabolt' after Canadian cross-country racer Geoff Kabush who requested a lighter weight setup without the standard QR lever, reportedly saves upwards of forty grams over a production 15QR thru-axle. That might be small beans to most riders but it's a worthwhile figure on a race bike that sees nearly all of its hardware replaced with titanium and aluminum aftermarket bits to create the lightest possible race weapon. But while the Kabolt might be neat, it's what's on the inside of the RAD 34 that makes it special.



Is the Damper Different?

We've spent some solid time on FOX's 2014 CTD equipped forks and have come away very impressed with how controlled the stroke is compared to the previous year's offerings, but it's safe to say that the RAD version of the damper isn't the same animal. The external stock CTD dials atop the right fork leg don't give anything away, however, and if you were to remove the CTD damper from the fork you'd find that it looks exactly the same as what's used within a production fork. It's a different story when it comes to the cartridge's inner workings, though, with a much more advanced layout that has been designed to provide enough support for a pro-level racer without taking away from the fork's ability to absorb the terrain. This has been accomplished by way of lighter damping at slower damper shaft speeds (think low-speed compressions like landing on a transition or applying the front brake) when the fork is set to its wide open 'Descend' setting, and while you might suspect that sort of setup would make for a fork that dives into its travel, the engineers at FOX have employed a mid-valve to help keep the it standing tall. What exactly is a mid-valve? While FOX wasn't about to delve deep into their pro-only RAD fork's inner workings, a mid-valve is essentially another set of shims and a check valve that sits behind the rebound piston to provide added low-speed compression damping. This certainly isn't a new concept, with it being relatively common in the world of motorbike suspension, and they are beginning to be employed more often on mountain bike suspension as well, despite the added complexity and cost that it takes to properly utilize them. The RAD damper also features more progressive damping at higher shaft speeds to help take the sting out of square edge impacts and flat landings that happen at pro-level speeds.



Slick Tricks

The RAD trickery doesn't end with the shims, though, as FOX's engineers go to great lengths to lower the fork's coefficient of friction in an effort to have it feel as slippery and active as possible. That begins with new dynamic seals throughout the fork that use an updated shape. FOX says that these seals, which require completely different seal bore dimensions and are therefore only on non-production RAD forks, significantly lower both breakaway and active friction within the fork. RAD models also see their damper rods given the Kashima treatment (ours was missing this upgrade, though), something that is only available to consumers on 2014 model year 40s, as well as new 20 wt. gold lubrication oil that testing has shown goes a long way to make for a more active stroke. One trick that wasn't done to our fork but that their top racers receive is having the bushings opened up ever so slightly by hand to further improve its action. According to FOX, the revised seals, Kashima coated rods, and new lube oil has meant that their racers are able to run roughly 10 PSI higher pressures without sacrificing any small bump sensitivity at all, an important fact when you consider how important that can be when talking about traction. Interestingly, the air spring side of the fork is entirely stock, with some team riders using oil volume to dial-in the progressiveness that they're looking for.



Getting RAD on the Trail

So, how does an ultra exclusive fork that has been assembled with the world's best racers in mind perform on the trail? Pretty damn well, as you might likely expect. When it comes down to it, suspension is always about compromises, with it being a balancing act between the shock or fork's available settings. Want a more active, supple stroke from your fork? That'll likely mean that it will also dive more into its travel when you're on the brakes or rolling into a steep pitch. More ramp-up to prevent hard bottoming? You might not get all your travel as often as you should. Similar give and takes make up a fork's performance throughout its entire range, but the balancing act becomes less and less pronounced (or at least it should) as the fork moves up in both hierarchy and cost. This becomes clear when you compare an entry level fork with a higher-end model that offers more control over damper settings, likely better tolerances throughout, and possibly a price tag with an extra digit to show for it all. All of the same can be said of the exceptionally rare RAD-spec FOX 34 FIT CTD shown here, minus the added cost because you simply can't purchase this fork regardless of how much money you walk into FOX's California headquarters with. But if you could get your hands on one of these, you'd quickly realize that the real advantage to the RAD 34 is how it manages to not compromise certain aspects of its performance nearly as much as a production fork, meaning that racers who have access to FOX's RAD program get to have their cake and eat it too.


That "cake" we're talking about refers to how the stiction at the top of the fork's stroke is implausibly low, with it making even the most active of production forks feel as if it was using sand for lubrication. And keep in mind that the RAD 34 that we rode didn't make use of a Kashima treated damper rod or bushings that have been opened up ever so slightly by hand, just the new dynamic seals and 20 wt. lube oil. Clichéd words like silky, supple, and smooth all jump to mind, but none of them really do any justice to how eager the RAD 34 is to slip into its stroke. How is FOX able to create a fork that is more sensitive than anything we've previously ridden? Those new seals and the lube oil change certainly help that cause but FOX puts a lot of it down to damper setup, which brings us back to that conversation about compromises. The RAD-spec damper's lighter low-speed compression setting, along with its trick mid-valve, holds the fork up high in its travel while also allowing it to be supple enough to take in and erase the smallest of impacts, and it's the type of performance that is literally the best of both worlds. We were actually convinced that the fork was both slightly under-sprung and under-damped after the initial setup and before hitting the test run but we ended up being proven completely wrong. Tune your own fork to be as supple as the RAD 34 and you'll likely end up plunging into three quarters of its travel every time you pull the front brake lever or roll into the steeps, yet FOX has managed to create a stable yet unbelievably supple stroke to their pro-level offering.



Running deeper into the fork's travel revealed a very controlled feel, with it never coming off as being overwhelmed when a bad line choice meant a head on collision with an immoveable rock was unavoidable. The RAD 34's O-ring told us that yes, we were going deep into the fork's stroke, but it was far less of a jolt than we would have expected. There was also noticeably less energy transferred through the bars during high-speed compression moments, with the fork doing well to mute square edges and flat landings in a way that a stock slider could only dream of. The difference couldn't even be called subtle, to be honest, and it took pointing it through a few taxing sessions to confirm that what we were feeling was real - this 150mm travel fork feels like it has at least an extra 10 or 20mm on hand to deal with those "oh shit" moments that pop up in a race situation. This was especially apparent when pushing hard while the fork was set to its stiffer 'Trail' setting, with it offering a more open and forgiving feel than the stock 34 without sacrificing any control.






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