The Big DUH Download: All About Our Latest Dropout

In the Beginning

At some point early in the development of our Sorceress trail hardtail, we faced a conundrum: we wanted you to be able to set it up single speed, like all of our long lineage of mountain bikes. We also wanted you to be able to use SRAM’s newish Universal Derailleur Hanger (UDH) system so you could easily source replacement derailleur hangers and use SRAM Full Mount drivetrains.

A set of printed technical instruction sheets showing multiple views of a rear dropout configuration, pinned to a light-colored wall.

The track-end dropout we’ve used on nearly all our other mountain bikes wouldn’t work. And anyway, we wanted something cleaner and more user friendly. This new design would need to stay true to some core Surly elements:

  • It had to be durable enough to put up with trail abuse
  • It had to be single-speed capable
  • It had to annoy some people on the internet

It was time to dust off the ol’ drawing board — er, envelope. “The genesis of the DUH dropout system started as a sketch on the back of an envelope addressed to my 2-year-old daughter,” said Ryan Callahan, the industrial design manager who helped bring this to life. And thus, a rough design was born.

One thing we like about this design is its visual simplicity: there are no dangly or swingy bits under the chainstay like other single-speedable UDH dropouts out there. Whether in geared or single-speed mode, it looks like it was made solely for that purpose.

There’s Always a Hiccup

Because this was supposed to play nice with SRAM’s UDH system, we showed it to them to make sure they were cool with it. They weren’t.

Our initial design was open-ended on the back, leaving part of the UDH barrel exposed and relying on our robust steel frames to contain the derailleur. SRAM wasn’t convinced it would work, so we fabricated a real working version, put it on a bike, and put it through a full winter of use without issue. Still, SRAM had doubts.

A collage showing a bicycle chainstay roller and related bike hardware in use. The top-left panel shows two dark metal roller components on a tabletop.

Then we thrashed the hell out of it in our product development shop, standing on it, yanking on it, yelling at it, hitting it with hammers, and simulating all sorts of other torture and documenting the results. We were pretty happy with how it performed. But SRAM? Still no.

A split-screen photo showing a person standing on a bike rear derailleur mount and dismounting a bicycle on a warehouse rack. The left side shows the bike on the rack with a person holding it steady, and the right side shows the man stepping off the rack while holding the bike wheel.

We went back to the envelope to beef it up.

A rendering of a green hardtail mountain bike shown on a clean white background, alongside a close-up inset of the rear derailleur and cassette area.

Success

Ultimately, we decided to address the literal gap in our design, filling it with a small chip that fully encloses and supports the UDH in geared mode. This was the key to making SRAM happy, and they gave us a big ol’ thumbs-up. In fact, they suggested that we patent the design (that paper is being pushed around at the U.S. Patent and Trade Office as we speak). This means that DUH has SRAM’s full UDH warranty and support. Thanks to those folks for working with us so closely on this.

A set of mint green metal bicycle components, including seat post clamps and chainstays, arranged in a clean grid on a light gray background.

So how does the DUH dropout work?

It may look like a lot of moving parts, but the system is simple:

In geared mode, a “chip” inserted into the driveside dropout provides a UDH interface. Another chip in the non-driveside dropout fills the axle slot to provide a simple, single axle position. This ensures your hub, rotor, and derailleur alignment stay dialed every time you remove and reinstall the wheel.

A collage showing a mechanical component from multiple angles: two physical parts on a beige surface, three technical line drawings with colored cross-sections, and a 3D rendered view of the assembly with a gray housing, black rod, and red inner ring.

For single-speed mode, replace the UDH chip on the driveside dropout with a chip that creates an axle slot with 16.5 mm of adjustment for chain tension. You’ll also need to install our single-speed-specific axle. A set screw in the front of the dropout prevents the wheel from slipping forward when pedaling. On the non-driveside dropout, remove the geared chip, leaving a traditional axle slot with a set screw on the back of the dropout to fight disc brake forces that want to push the axle rearward.

Three close-up product detail shots of bicycle drivetrain components, including a blue crank arm, a silver chainstay and cassette, and a copper-colored chainstay with a silver cassette, set against a dark background.

We think the DUH system is efficient and effective, but we’re not its only fans — Big Bike Media had a few nice things to say about it too. Our pals at BikeRadar said, “Like many of the best problem-solving ideas, Surly’s patent-pending DUH dropout is delightfully simple.”

Close-up of a metallic gold bicycle frame showing the seat tube junction, bottom bracket, and part of the head tube on a white background.

BikeRumor hailed it for providing “compatibility with SRAM UDH, Full-Mount, and single-speed drivetrains in a single frame. Blamo. This is the kind o’ versatility Surly is known for.”

Close-up of a bicycle wheel and drivetrain with a chain guard and cassette, photographed outdoors on a blurred forest path.

If you’ve read this far, you’re probably thinking, “OK cool. But if DUH is so great then why isn’t it on more Surly bikes?”

Patience…

Close-up of a muddy mountain bike rear wheel, chainring, cassette, derailleur, and part of a rider's legs and feet on a dirt trail.

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