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Bottom Bracket Confusion?????

Posted by BM on Sep 11th 2020

Bottom Bracket Confusion?????

Confused about which bottom bracket you have or that you need for that new build? You are not alone! Today, there are two main types that you will find 1) threaded and 2) press-fit bottom brackets. Most threaded road bottom brackets use a 68mm-wide shell with a standard threaded left side and reverse (left-hand) threaded right side. You can still use the old tried and true square taper bottom bracket, or one of the more modern outboard bearing types, which rely on a crankset featuring its own integrated axle/spindle. Outboard bearings were introduced in the early 2000’s, and for the most part they  use a 24mm steel axle, and became the standard for anything but true entry-level bikes – which still often use the square taper bottom brackets.

To really complicated things we have to look a the press fit bottom brackets and all the variations that come with it. Rather than threading into the frame, they rely on a large bearing press for installation. The main reasons for their introduction were to reduce weight and increase stiffness via larger-diameter 30mm spindle. They also greatly speed up complete bike assembly at the factory, which is probably why they became so popular so quickly. Here are some of the most common varieties of press fit Bottom Brackets:

BB30: Uses a 68mm x 30mm aluminum axle; bearings press directly into the frame. It’s rare to find a true BB30 frame anymore because PFBB30 is better.

PF30 / PFBB30: Same as mentioned above, but the bearings are pre-pressed into a plastic or nylon sleeve that presses into the frame. Usually and easier installation and cheaper frame manufacturing – no precision-machined aluminum insert required. The composite cups that hold the bearings can make up for minor a frame intolerance, and they also help minimize the creaking that sometimes occurs in a BB30 setup.

BB86 or PFBB86: Relies on a slightly smaller bottom bracket shell than PF30, using a bearing size intended for a 24mm steel crank spindle (which would otherwise be used with a standard threaded bottom bracket shell and outboard bearing bottom bracket).

BB386EVO: The “best-of-all-worlds-and-compatibility” for future-proofing. Originally, road bike bottom brackets were  68mm wider (or sometimes 73mm). BB386 moved this outward to 86mm, the idea being to allow frame manufacturers to create wider, stiffer bottom bracket sections to improve power transfer. This required a longer crank spindle, which was called BB386EVO. While some frames require a BB386 crankset because they have the wider BB shell, a BB386 crankset will usually also work in a BB30/PF30 frame by adding a series of spacers.

The Takeaway: Most newer road bikes are shipped with PF30 or BB386, and that is all you will ever need. For some riders, they’ll work great and are easy to upgrade. If you ever start developing any play or creaking, upgrade to a thread-together bottom bracket that adds a few grams but mostly eliminates any of the creaking or misalignment issues of press-fit designs will solve your issues. If you ever have questions as to the right bottom bracket for your bike or crankset upgrade, don't guess. Give us a call at 336-501-3227 and we will help you find what is right for your situation!