Closeup view of a bike frame with a bushnell bottom bracket installed.

Bushnell Eccentric Bottom Bracket: The Time-Tested Tensioner

If you’re looking to build a singlespeed or tandem bike, or use an internally geared hub, proper chain tension is essential. There are a variety of options for single-speed chain tensioning, like spring-loaded tensioners or horizontal dropouts, but these add clutter to your rear triangle. The cleanest solution is to use an eccentric bottom bracket. And now, the Bushnell Eccentric Bottom Bracket, the undisputed champion of chain tensioning solutions, is a part of the Problem Solvers lineup.

A black Bushnell bottom bracket on a white background

An eccentric bottom bracket is actually an adapter that holds English threaded bottom brackets and allows users to adjust the fore-to-aft position of the crankset to add tension to their chain. This is done by rotating the off-center (or eccentric) axle position within the round frame shell to move it forward and pull the chain taut. This type of mechanism has been commonly used by tandem and singlespeed riders for decades and are still popular thanks to their clean aesthetics, ease of use and reliability. But the eccentric bottom bracket wasn’t always this good.

Old eccentric bottom brackets were held in place by threaded screws in the bottom of the frame.

Closeup view of an older iteration of a Bushnell eccentric bottom bracket.

These screws would often be stripped or damage the EBB by over-tightening.

An older Bushnell eccentric bottom bracket with lots of damage.

The original eccentric bottom brackets from the ‘70s, were heavy aluminum chunks held in place by either tightening a split frame shell or screwing sharpened bolts through threaded holes and into the EBB. Neither option was really great, as the pressure was only applied to a small area and overtightening could easily strip the threads, bend the frame shell, or gouge the component. So, in the late ‘80s, builders developed an eccentric mechanism that didn’t depend on screws or the frame at all. Instead they used a split/wedge design, commonly seen on quill stems, to apply tightening pressure inside of the shell. This avoided the problems of earlier versions, but still required some hammering to adjust, which could easily cause damage if not done carefully.

The split-wedge EBB was an improvement, but nobody wants to use a hammer for a simple adjustment.

A split wedge Bushnell eccentric bottom bracket on a white background.

In the early ‘90s, Dennis Bushnell invented what would become the gold-standard of eccentric bottom brackets that we have today. It used a winged design that applied pressure more evenly around the entire circumference of the shell and could be easily tightened or loosened to adjust positions at any time. Since then, the Bushnell design has been continuously improved, resulting in the reliable, lightweight components that we have today.

Problem Solvers now carries a wide variety of Bushnell Eccentric Bottom Brackets, including classic and fat bike versions like this one

A modern Bushnell eccentric bottom bracket on a white background.

As the exclusive provider of the Bushnell Eccentric Bottom Bracket, we are thrilled to bring this industry-leading solution to riders like you. As the saying goes, we won’t try to fix what isn’t broken, so you’ll still get exactly the same high-quality product you expected. Got a Bushnell EBB on your bike? Tag us in your bike photos on Instagram @ProblemSolversBike! And submit any other bike problem ideas here. Finally, come back next week to learn how to install and adjust an eccentric bottom bracket.

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