Canadian mountain biker Geoff Kabush just shared the prototype reverse arch FOX RAD short-travel gravel suspension fork he’s been testing around Moab, UT. It looks nothing like the Fox AX gravel forks we’ve seen in recent years, but reminds us (and many of his fellow MTB pros) of decades-old mountain bike suspension designs from the likes of Manitou & RockShox. And with a key Answer patent set to run out this year, we have a pretty good idea on how soon this thing could make it to market…

FOX RAD prototype reverse arch, short-travel gravel suspension fork

FOX RAD prototype gravel fork, reverse arch 30mm short-travel gravel bike suspension, courtesy Geoff Kabush Moab UT White Rim FKT attempt

all photos c. Geoff Kabush

We don’t know a ton of concrete details about the Fox R.A.D. prototype gravel fork, but we do know that Kabush has been riding in the Utah desert on his OPEN WI.DE. in an FKT attempt around the 100 mile White Rim trail loop and 140mi Kokopelli Trail. Most often completed on a mountain bike, Kabush seems to have opted for a lighter weight setup with 700x40mm Maxxis Receptor semi slick gravel tires… and this 30mm travel reverse arch Fox RAD prototype.

While we wanted to believe that R.A.D. stood for Reverse Arch Design, it is in fact the name of Fox’s prototype division Racing Application Development. That’s the same division that developed the Open Project that became the 40mm travel AX Adventure Cross gravel fork, but this is something altogether different…

Tech details

FOX RAD prototype gravel fork, reverse arch 30mm short-travel gravel bike suspension, courtesy Geoff Kabush, detail

all photos c. Geoff Kabush

Without an official statement from Fox yet, Kabush’s close-up spy shot gives us plenty to work with, so why do we think this fork gets just 30mm of travel?

Based on the 32mm stanchion AX with 40mm of travel, this definitely looks like it has less slider exposed. If it is also 32mm stanchions, it seems like there is about 30mm of exposed tube between the main seal and the forged crown, which is angled to provide the fork offset.

Another standout feature are the dramatically tapered fork legs. Somewhat like a smoother transition version of Step-Cast, the legs appear to taper in several dimensions to a slim thru-axle dropout.

We can also glimpse on the non-driveside that it fits a flat mount disc brake. Based on the XTR rotor shaping we know it is a 160mm rotor, and it looks like caliper is in the lower position on the fork leg, suggesting compatibility with 160 or 180mm rotors.

Reverse arch patent?

Answer Manitou reverse arch fork patent

Most notably of all though is of course the reverse arch design, which was always said to offer an excellent balance of stiffness at low weight, but isn’t that patented? Yes, but there’s the trick. Answer (which later included Manitou, now owned by Hayes) filed their reverse arch suspension fork patent on October 17, 2001. That means, that US patent #6607185B2 is set to expire in October of this year.

That doesn’t mean that Fox is going to start selling you reverse arch gravel forks start this fall, but they could…

rideFOX.com

23 comments

  1. Erik on

    I wish I worked in marketing for Manitou when Fox releases this. I would build an entire marketing campaign around this.

    Reply
  2. Joenomad on

    Maybe it’s the angle of the photo, but the reverse arch looks like it can get really close to the downtube when the fork is fully compressed.

    Reply
  3. john v on

    I think it’s time Cannondale, and Action Tec bring back their below the headtube suspension. I rode a Cannondale road bike in the mid to late 90’s that had 30-40mm of travel under the headtube, old timers certainly remember this design. I also had a custom steel Curtlo frame with the Action-Tec headtube shock, I can’t recall travel, 60-80mm I think, and it was awesome. Rock solid, light, and with steel fork legs and steerer, custom builders could easily incorporate it. This would be great for gravel bikes. Many of them have long headtubes anyway, so you’d lose very little to just doing it with a carbon frame.

    Reply
      • John V on

        Never knew the name. I borrowed it on a group road ride, the only road ride I’ve done in 30 years actually. Ny buddy owned a Cannondale dealer and asked if I would go. He knew I was a mtbr and let me ride the bike. I’ve wanted one like it for years. Was seamless, light, and really worked well. Seems like a no brained for gravel bikes, and, fat bikes too. The Action Tec shock was solid as a rock. Would make a great fat bike system. Hanenbrink had a beach fat bike 30 years ago with a similar system.

        Reply
        • Dan Reese on

          I had a Cannondale XS800 cross bike that had 25 mm of travel with headshok. It was perfect for gravel. Rode it in Iron Cross in 2006. Just enough travel for bumpy rutted gravel roads and complete lockout. No proprietary front hub required. I sold that bike a couple years later and have regretted it ever since.

          Reply
    • Ol' Shel' on

      Other designs have shorter axle-to-crown heights. People are fickle, and they want their road-ish bike to look as much like one as possible.

      Reply
    • Tim on

      Yes! Absolutely! Amazing short travel forks- sensitive, supple, light, torsionally rigid, easy access lockout switch, upgradeable internals.

      Reply
  4. Smokestack on

    You don’t invest in tooling for molds if you don’t intend to bring the product to market. Now the Manitou haters are gonna have to pick their feet out of their teeth. It will be interesting to see if they take the reverse arch to their MTB line as well.

    Reply
  5. Jason D West on

    All the Manitou fanatics will say l told you so! Its only a matter of time before the competition uses the reverse arch

    Reply
  6. WhateverBikes on

    There’s at least ten bikes in Cannondale’s current range that have the HeadShock suspension. None of those are in the MTB, race or gravel lineups thouhg. Seems like a no-brainer for gravelbikes.

    Reply

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