Carbon Fiber Sucks at Threads

January 25th, 2020 by / In Tech

Obviously we love carbon fiber. After all, it’s the material we chose to make our bikes. Carbon fiber has many characteristics that make it ideal for bikes; lightweight, strong, and highly “tunable”. But there are some things it’s not so good at, and one of those things is threads. And in the case of the bottom bracket – which has a very fine thread pitch – it really sucks.

Carbon fiber does not generally perform well because of the small cross-sectional area of the threads. It is unlikely that the fiber volume will match that of a typical composite. So we assume the worst-case scenario, which is that the thread consists of only the epoxy resin portion of the carbon fiber composite. When comparing the mechanical strength properties, the titanium is generally five times stronger than epoxy. So by bonding a titanium insert into the BB, the integrity and life of the frame improves.

Many manufacturers have chosen to offer threadless (pressfit) bottom brackets. They are a cheap, light, easy alternative to threads. But there is one problem; threadless bottom brackets suck too. They are creaky and the BB can move around inside the frame. What we decided to do at Pursuit is bite the bullet and invest in the added complexity, cost and time needed to bond in a threaded metal shell. We could have opted for aluminum. Aluminum is cheap and light, but it runs the risk of galvanic corrosion. So instead we opted for the more expensive, yet vastly superior titanium for our BB shell inserts. While they cost a lot more, they proved a perfect solution to the “thread problem”. 

In the case of Pursuit Cycles and the LeadOut Road and LeadOut AR, we chose the T47 BB standard. We chose it because it will fit just about any crank and provides enough access to easily fish wires, cables, and brake hoses. Additionally, its size lends itself to our big beefy BB area.

The BB is just one of the areas we chose to go the more expensive route because it creates a better bike. There are more, and we’ll feature others in future newsletters.

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