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Cycle Monkey

Internal Gearing Specialists, Bicycle Distribution & Service Center

Soma Rush Fixed Gear with Belt Drive

When a local customer contacted us about building a belt drive-equipped fixed gear for him, we were excited to execute his vision. He wanted a bike that would be simple, lightweight, and durable for commuting around town quickly. He gave us a few general guidelines for the build but asked us to make our own recommendations for parts that would fulfill his requirements. His primary requests were that the frame be chrome colored and that he could use a belt drive system. He planned to use the bike to zip around Oakland and commute across town to work - primarily short, fast rides without much climbing.

After some research, we decided the SOMA Rush frame would be a perfect fit. SOMA is based in San Francisco and offers a wide range of affordable heat treated chromoly steel frames that are resilient and versatile. SOMA has a reputation for making strong, no nonsense bikes, which matched our customer’s criteria perfectly. The Rush frame has a few features which make it unique compared to many track bikes on the market. It has nimble track-style geometry, with a steep headtube angle and short rear end to keep it nimble while retaining generous tire clearance. It also has the looks of a classic road bike and weighs only four pounds including the frame and fork set. The stock chrome color is especially eye-catching and scratch resistant. Investment cast horizontal dropouts and a one inch diameter headtube add to its vintage appeal.

As soon as we received the frame we sent it to a local frame-builder to have a belt drive splitter installed, and before long we had the freshly modified frame in hand ready to build up. While we waited for the frame to come back, we started putting the build kit together. The customer wanted bullhorn style bars, a comfortable, light-weight saddle, durable toe straps, and tires that would hold up to rough roads and stop skids. For handlebars, he chose Profile Design’s T2 Wing Base Bar, which has a time trial oriented design with a flattened aero grip area closer to the stem for a more ergonomic secondary riding position. For the saddle he chose a slate colored Brooks Cambium saddle, made of cotton canvas and vulcanized rubber. The Cambium is Brooks’ first non-leather saddle, and its rubber construction requires no break-in time, unlike their traditional leather saddles – it’s comfortable to ride right out of the box.

He chose toe straps over flat or clip-in pedals so that he could use his regular shoes for commuting, yet maintain a high degree of pedaling efficiency. Fixed gear bikes ride better with foot retention like toe straps or clipless shoes, so the rider can control the speed of the rear wheel by applying backward pressure to the cranks as they rotate. Because the cranks are moving at all times, it’s important for a rider’s feet to stay securely connected to the pedals. In this case, a pair of Power Grips were used, which attach diagonally across the pedal and allow the rider to easily get out of the pedal with a twist of their foot. Lastly, we installed Schwalbe's puncture resistant Durano tires, with a thicker version in the rear for longer tire life when performing skids.

For the wheels, the customer wanted deep section, aero-style rims in white. Also, since he requested a front brake only because he planned to control the fixed rear wheel with his feet and legs, we hoped to find a matching set of rims with a machined brake surface for the front wheel and a non-machined rim for the rear wheel. H PLUS SON offered a solution in the form of the 42mm tall SL42 (front) and Formation Face (rear) rims. These rims are mated to track hubs made by Phil Wood, another local company that has gained a sterling reputation over the years for high quality machined bicycle parts, made right down the road in San Jose. We laced the front wheel with a radial lacing pattern for a racier look and the rear wheel three cross for greater strength. Both wheels used silver Sapim race spokes and brass nipples.

The Gates Carbon Drive belt system was a high priority for this customer. He loved the fact that belt drives are quieter than chains and won't leave messy grease stains on your legs – a realistic consideration for commuters who are riding in their regular work clothes. Chain wear is especially noticeable on fixed gear bikes when riders change from pushing forward on the pedals to drive the bike to pushing backwards to slow down. Wear or looseness in a chain results in an undesirable knocking noise and feel. As the drivetrain wears, chain tension needs to be adjusted regularly to prevent this knocking. Belt systems are ideal for fixed gear use because they not only wear slower, but they are also set up with pre-tension, so there is never any play in the drivetrain. You get instant power transfer in both directions.

If at some point he decides that having just a single gear ratio is too limiting, there is the option of adding the Schlumpf 2 speed crankset to the existing drivetrain. The Schlumpf cranks are the only way of adding multiple speeds to a fixed gear without removing the wheel. The Schlumpf cranks do no require an external shift lever, since the crank arm has a built in shift button that can be actuated by tapping it with your heel. We carry several different gearing options to accommodate different gearing requirements, including the Mountain Drive version which offers a 250% easier climbing gear. We posted previously about this Cinelli we built using the Schlumpf Mountain Drive crankset.

Build Details: 

• Frame: SOMA Rush 59cm
• Fork: SOMA Rush
• Headset: Chris King
• Stem: Thomson Elite X4
• Handlebar: Profile Design T2 Wing Base Bar
• Grips: Brooks Leather
• Seatpost: Thomson Elite X4
• Saddle: Brooks Cambium
• Seat Clamp: SOMA Rush integrated
• Front Hub: Phil Wood Track
• Rear Hub: Phil Wood Track
• Spokes: Sapim Race
• Nipples: Sapim Brass
• Rims: H PLUS SON SL42 front, H PLUS SON Formation Face rear
• Tires: Schwalbe Durano front, Schwalbe Durano Skid rear
• Cranks: Sugino Messenger
• Pedals: MKS Promenade EZY with PowerGrips toe straps
• Bottom Bracket: Sugino
• Sprockets: Gates Carbon Drive
• Chain: Gates Carbon Drive
• Brakes & Levers: Paul Components Cross Lever, IRD B49 Dual Pivot Caliper