Building A Single Speed Specific Mountain Bike Frame

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Last week, we took a look at the nuts and bolts required to convert a standard mountain bike frame over to a single speed. As the single speed craze caught on more steam, the mountain bike community started integrated methods typically found in commuter bikes to develop single speed specific mountain bikes with integrated methods of adjusting chain tension. If you are ready to completely jump into the deep end of shiftless mountain biking, here are your options as you look to buy or build your dedicated SS rig.
Eccentric Bottom Bracket Single Speed Frames

An eccentric bottom bracket is an over sized bottom bracket that contains a shell that rotates the crank axle off axis of its normal position. This brings the crankset closer and further away from the rear axle as you spin it within the bottom bracket shell of the frame. The two most common styles of this bottom bracket are secured inside the frame via set screws through the bottom bracket shell or via expansion bolts in the eccentric assembly (like the Bushnell). The result is conventional dropouts in the rear (can be spec’ed with or without a rear derailleur hanger) and chain tension handled in the front by the EBB.
Positives on the EBB

• Conventional dropouts just like with a regular mountain bike.
• Can fine tune chain tension easily when chain stretches.

Negatives on the EBB

• Metal to metal contact of EBB and bottom bracket shell is prone to creaking.
• You are actually changing the crank position in relation to the saddle when adjusting chain tension.

Horizontal Dropout Single Speed Frames

Horizontal dropouts were first seen on track bikes to adjust for chain tension. With horizontal dropouts, your conventional rear dropouts are replaced with horizontal slots that handle chain tension. Pretty simple concept really…you are moving the rear axle on a horizontal plane. It is normally recommended that you use a through bolt axle on these systems as the standard quick release can slip much easier due to its inability to apply the same clamping force as a bolt through design. You also have to adjust the caliper position if you are using disc brakes as you move the axle. For this reason, the rear IS caliper mount is slotted as well.
Positives on Horizontal Dropouts

• Crank axle and bottom bracket assembly is like you would find on a regular mountain bike frame.
• Ultra cheap frame options that are easy on the budget.

Negatives on Horizontal Dropouts

• Have to adjust rear caliper with axle.
• Through bolt means you lose the convenience of the quick release on the trail.
• Have to make sure the wheel is straight in the dropouts for proper alignment.

Sliding Dropout Single Speed Mountain Bike Frames

Sliding dropout single speed mountain bike frames take the horizontal dropout theory and extend it to give you conventional styled dropouts and brake mounts that move with the sliding assembly. The entire rear dropout assembly slides in the frame giving you the chain tension adjustment needed on single speed mountain bikes, but does it all with setup you are used to on regular frames. (Paragon sliders are the most common form of this setup)
Positives on Sliding Dropouts

• You get standard dropouts that can also include a rear derailleur hanger for conversion back to geared.
• Can use standard quick release rear axles.
• Bottom bracket unaffected.

Negatives on Sliding Dropouts

• Have to make sure rear axle is straight in frame for proper alignment
• One of the more expensive options in single speed setups.

Single Speed MTB Frame Options: Making the Case

When you go to choose which setup you are going to have on your single speed specific frame, you really have to weigh a lot of options.
The Manufacturer and Bike: How It Rides

Ultimately, it all comes down to the ride. If you have test ridden different mountain bike frames and you found one that fits your needs, you will just have to work with whatever system comes with that frame. I do not see any reason to jump to a different frame purely over the method of adjusting chain tension as that is a small part of the overall picture.
The Custom Build

If you are going with a complete custom build, you need to take a close look at each option to see which one fits in your needs. Custom frame builds see the sliding dropout and EBB options in most situations as the budget allows for a more high end solution. I have had both the EBB and Paragon Sliders in my custom builds and I like the simplicity and creak free operation of the paragon sliders the best out of those two options.
Single Speed Mountain Bike Budget

If you are on a tight budget for this new rig, take a look at frames from Surly and Vassago which both provide great riding steel single speed mountain bike frames that will not get you divorced. You are not going to get the pretty welds, carbon frames or fancy chain tension setups, but you will be in a SS specific frame that you’ll be able to ride day in and day out.
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