Kathy Sessler showed us some pics of the Santa Cruz Syndicate receiving and testing some prototype forks from Fox. From the pictures, we can say for sure that the new fork is a different platform. It's lowers are slender and the dropout extensions are visibly lightened. The Kashima-coated stanchions tubes are still 40-millimeters in diameter, but the fork looks far more compact than the previous 40. Behind the upper seal-heads are curious bosses with what appears to be fittings for threaded caps. There are a number of explanations for the unusual bosses: the simplest being a mounting position for a fender or a mud flap; or possibly a port for a remote spring preload adjustment (a feature common to road racing motos); with the most far-reaching guess being the integration of an electronic damping control.
Greg Minnaar inspects his proto Fox 40 RAD fork while Fox's Mark Fitzsimmons brings him up to speed on the features. Notice the bosses on the inside of the fork near the seal-heads and the super-slim sliders. Kathy Sessler photo
What Fox Racing Shox Has to Say
Mark and Greg inspect the new lowers and dropouts of the 40 RAD fork. The dropouts are visibly smaller, as is the entire slider chassis. Kathy Sessler photo
Fox Racing Shox would not comment on the new fork officially beyond saying that the name of the new fork is 40 RAD ( Racing Applications Development) and that it is truly an all new fork. Fox suspension guru Mark Fitzsimmons said that 90-percent of the 40 RAD fork's internals are retrofittable to previous 40 forks, which leads one to believe that 40 owners can upgrade to most of the 40 RAD's performance features.
About the fork, Mark Fitzsimmons said he would only speak in the broadest of terms: "Every part of the chassis is new. The goals were to design in some chassis compliance, keep the same stiffness, reduce unsprung weight, and to change the mass location. It does have a new damper that is designed to work with the new spring system."
About That New Spring System
(Clockwise) The original Fox 40 on left is huge-looking by comparison to the new 40 RAD prototype fork. Note the raised section at the seal head - just enough metal to house the bushing and wipers. The 40 RAD fork crown has a new profile as well and its underside is more squared off. The new dropouts retain the dual pinch-bolts of the original, but are smaller, lend us to believe that the sliders may be no longer made from cast magnesium. Kathy Sessler photo
Fox and Trek developed a hybrid air/coil spring system for the Fox 40 equipped Session 9.9
that incorporates a titanium coil spring which is augmented by compressed air (an innovation well proven by the Marzocchi 888 and 55 forks). Trek initially had exclusive use of the Fox hybrid spring for the Session, which employs a standard shock pump to tune the fork spring, but now it appears that the same or an upgraded version will now appear on the new 40 RAD fork. The advantages of a hybrid air/coil spring are that it spring rate can be fine tuned for any track or weather condition, and that one spring can handle a wider variety of rider weights. Of course, any percentage of the fork's coil-spring rate that can be augmented by compressed air will also save a considerable amount of weight.
In a later communication, Mark Fitzsimmons corrected PB's guess that the 40 RAD's spring was a hybrid: "The spring system is unlike anything out there in the gravity suspension world. It is a 100% FOX design that has several different adjustments for individual riders' weight and riding style. It is not a hybrid system. The Trek World Racing team races on FOX designed spring systems."
Why the Skinny Sliders?
PB photographer Colin Meagher got this closeup of the bosses behind the seal head in the pits at Val di Sole. Interesting that the center appears to be a button of sorts - Air bleed valves? Negative spring adjustment?. (Note: Fox released at Val di Sole that the function is to bleed air from the lowers.).
This is only guessing, but there is a possibility that Fox switched from magnesium lowers to aluminum. Aluminum is heavier than magnesium and in theory, magnesium has a better stiffness-to weight ratio, but magnesium can be quite porous, so it does not lend itself to thin castings. If Fox figured out a way to 3D-forge its fork lowers from aluminum in the same way that it produces its shock bodies (Squishing a billet of heated aluminum with such force that it gells and flows through the mold like plastic, producing a nearly finished part.), an aluminum slider could be created that would be thinner, stronger and lighter weight than its magnesium counterpart. While this is only guessing, Fox certainly has the intel and the resources to implement such a wild strategy.
When can I get a 40 RAD Fork?
Peaty and Josh Bryceland testing the prototype Fox 40 RAD forks in preparation for the Val di Sole World Cup DH. Kathy Sessler photo
Our bet is that the 40 RAD will be in production soon. While the new fork is still in prototype form, Fox Racing Shox has always put its customers needs ahead of its racing development strategy. Fox would not have developed the 40 RAD if it had no intentions of bringing it to market. Expect to see the fork OEM on DH bikes in mid 2013 and at your most lucky LBS about the same time. Until then, all eye will be on Santa Cruz, Trek, Scott Lapierre, GT and Morewood riders at Val di Sole this weekend
to see how Fox's 40 RAD holds up under the heat of World Cup DH competition.