Fitting wide tires and/or fenders between road cranks can be a challenge. René Herse was a master of frame design, who curved his chainstays ‘just so’ to create the room he needed. On the tandem above, not a single millimeter is wasted, and the result are perfect clearances for 42 mm-wide tires, fenders and cranks with a narrow Q-factor.
The first step toward replicating Herse’s mastery in modern bikes was to make a bottom bracket shell with the correct angle for curved chainstays. We already offer this shell for standard-diameter tubes. Brand-new is the same shell for oversized down tubes. These parts eliminates the need to ‘blacksmith’ the chainstay sockets of BB shells designed for straight chainstays.
There are many ways to bend the chainstays. To obtain easily replicable results, Hahn Rossman machined dies that fit perfectly over the chainstays. They create a beautiful curve without kinks or bulges. We’ve developed the exact shape through CAD design and the experience of building numerous bikes with curved stays.
Curving stays is a labor-intensive process, to say nothing of the time and effort to make the dies, but it’s almost a necessity for modern all-road bikes.
We now offer the curved chainstays ready to go. They also are indented slightly on the inside to increase the clearance further, without creasing them as you often see on older bikes. The curved chainstays are a perfect match for the Compass bottom bracket shells. They are available separately or as part of the complete tubesets that we’ve developed in collaboration with Kaisei, the Japanese maker of top-quality steel tubes
Also new in program are lighter-gauge chainstays, which balance the stiffness of our ‘Superlight’ tubeset.
As a final part of the puzzle, Hahn also made a gauge that visualizes the required clearances for a Rene Herse crank (177 mm length) with a 48×32 chainring combination. If the gauge fits, then your cranks will work with the recommended 110 mm bottom bracket. And since Rene Herse cranks have one of the narrowest Q-factors and a standard road chainline, other cranks will fit as well.
If the gauge fits, then smaller chainrings and shorter crankarms will fit, too. If you need more room, space out the cranks with a longer bottom bracket spindle. This gauge takes the guesswork out of the parts you need to order.
The photo above shows a fillet-brazed frame, because the new bottom bracket shell for OS tubing wasn’t available yet. With the new BB shells and curved stays, standard road cranks, even those with a narrow Q-factor, will fit, unless your rear spacing is much greater than 130 mm.
When I built my Mule (above), it was intended as a prototype for a modern all-road bike that can travel with speed and comfort over any distance, on any road and in any weather. Over the last few years, we’ve productionized most of the parts used in this build. Creating a custom all-road bike has never been easier!
- A series of blog posts about our Kaisei tubesets
- Information about framebuilding parts in the Compass program