Ultralight, Rohloff-Equipped Cannondale Flash Mountain Bike

These photos were submitted by one of our customers in British Columbia, Canada.  His Cannondale Flash carbon fiber mountain bike weighs in at just shy of 20 pounds without pedals, making this the lightest Rohloff SPEEDHUB 500/14-equipped bike that we have worked with.  The carbon frame is as light as many high-end road frames and the parts spec includes plenty of lightweight carbon bits.  The Lefty fork also helps bring the total weight down.

This customer purchased a Rohloff SPEEDHUB 500/14 from us last summer for his tandem and fell in love with its shifting performance.  So, when replacing his mtb this spring, a Rohloff SPEEDHUB 500/14 was his preferred drive train for the new bike. We built up the wheels and helped troubleshoot a few installation complications.

For the wheels, we laced the Rohloff rear hub and Project 321 Lefty-specific front disc hub into No Tubes Crest rims using Sapim Laser spokes and alloy nipples.  This gave the customer a lightweight wheelset to complement the rest of the bike.  We have long been fans of the No Tubes rims for their ease of tubeless tire setup and chose the Crest model for this build based on a light weight rider.  The Crest model is billed as a general XC rim and is offered in 26", 650b/27.5", and 29" sizes.  Its 24.4mm width is typical for an XC rim, but at 340g, it is lighter than just about all other aluminum rims on the market.  We generally prefer to use these rims for lighter riders or race day wheels for moderate weight riders.  The Laser model is a thin double butted spoke from Sapim that sheds weight without the higher cost of the bladed CX-Ray model and also makes for a more comfortable wheel.

As with many current mountain bike frames, this Cannondale Flash frame has post mounts for the rear brake instead of the traditional international standard mount.  This makes our Monkey Bone (or Rohloff Speedbone) incompatible with the frame and the torque arm must be used to keep the rear axle from rotating during use.  Normally when using the torque arm, the cable box gets oriented so it points upward and the cables loop up and over the brake caliper and along the left seat stay.  This is done because there is interference between the cable box and the torque arm if the cable box is positioned under the dropout for our preferred cable routing along the left chainstay.

On this frame, the position of the post mounts caused interference with the cable box if it was oriented such that the cables would loop up and over the brake caliper.  The only cable box orientation that cleared both the torque arm and the post mounts was to point it downwards and loop the cables under the torque arm.  We ran into the same issue on this Spot Acme conversion, which also has post mounts instead of an IS mount.  Functionally, this orientation shifts just fine, but it does position the cables closer to the ground as well as create a loop that could snag a branch.  In the photos, the cables dangle quite far under the torque arm, but the customer has since anchored them to the torque arm with a reusable zip tie as we did with the Spot Acme mentioned above.

Chain tension is controlled by a Beer Components BB30 eccentric.  These US-made eccentrics allow a frame with standard vertical dropouts and an oversized BB30 bottom bracket to be set up without a chain tensioner.  The only caveat is that you have to use a crankset with a 24-mm integrated spindle, such as the Race Face Turbine; square taper or BB30 cranksets will not work.  Also now available from Beer Components is a slightly larger diameter version for Press Fit30 bottom bracket shells, which are becoming the standard shell size for BB30-compatible frames.


Build details

• Frame: Cannondale Flash carbon fiber

• Fork: Cannondale Lefty Max Carbon XLR

• Headset: Cannondale

• Stem: Cannondale for Lefty

• Handlebar: Ritchey WCS Carbon

• Shifter: Rohloff

• Grips: Ergon GP1 for Rohloff

• Seatpost: Ritchey WCS Carbon

• Saddle: Tioga Spyder

• Front Hub: Project 321 Lefty

• Rear hub: Rohloff SPEEDHUB 500/14

• Spokes: Sapim Laser

• Nipples: Sapim Alloy

• Rims: No Tubes Crest

• Tires: Schwalbe Racing Ralph

• Rear Skewer: Shimano XT

• Cranks: Race Face Turbine

• Bottom Bracket: Race Face X-Type

• Chainring: Race Face Single

• Chain: Wippermann 8sX

• Brakes: Avid XX

• Rotors: Hope/Avid 160/160mm