The buyer's guide to choosing the right bottom bracket

Your bike’s bottom bracket has a tough life! It has to handle all the power you put through the pedals, and its bearings are constantly working while you're turning the cranks. Also, positioned at the bottom of the frame, it's right in the firing line of water sprayed up from wet roads.

Not surprisingly, the bottom bracket's performance will eventually start to deteriorate. It might start to creak and click, or the bearings could feel rough when you pedalling.

Most bottom brackets aren’t serviceable. They're designed as sealed units to be thrown away and replaced when they no longer do their job correctly. For example, the Shimano Deore threaded bottom bracket has “do not disassemble” printed on it.

If your bottom bracket starts to creak, you could try removing it from the frame and reinstalling it, but if the problem is inside the bearing and it's a non-serviceable design, it's time for a new one.

There are lots of different types of bottom brackets out there. Essentially, though, they can be divided into threaded and press-fit varieties.

Your bike will be designed to suit a particular type. You can’t fit a threaded bottom bracket into a frame designed to take a press-fit bottom bracket or vice versa.

Beyond that, there are various types of threaded bottom brackets and various kinds of press-fit. Even bottom brackets that look similar can have slightly different dimensions, meaning they’ll only work with specific bikes and chainsets.

A threaded bottom bracket screws into a frame with threads cut inside the bottom bracket shell. One common type is a cartridge bottom bracket, such as the Shimano BB-UN55.

Most cartridge bottom brackets are two parts: the bearings and spindle are contained in the main body, which screws into your frame’s bottom bracket shell from the drive side, and an adaptor screws in from the other side.

The ends of the spindle are shaped in various ways to work with different chainsets. For instance, the Shimano BB-UN55 bottom bracket is square taper, so it’ll work only with square taper chainsets, while the VP604 bottom bracket uses an ISIS splined design, so the chainset needs to be made with holes that match.

You also need to know the width of your bike’s bottom bracket shell – 68mm is common – and the length of the cartridge bottom bracket you’re after. That info will be written on the body of the one you’re removing; failing that, you can easily measure with a ruler. For example, we offer the Rockrider square taper bottom bracket in various lengths from 110mm to 131mm.

Other threaded bottom brackets have external bearings, and a larger diameter hollow spindle is attached to one of the cranks. The idea is to allow the manufacturers to increase stiffness and reduce weight on sports-type bikes. Of course, these bottom brackets work with different chainsets.

For example, the Shimano Deore threaded bottom bracket is an inexpensive option that fits both 68mm and 73mm bottom bracket shells and works with standard 24mm-diameter chainset spindles.

Rather than screwing them into place, press-fit bottom brackets push into frames specifically designed to take them.

Press-fit systems were introduced to allow frame manufacturers more scope for design innovation, allowing them to bring down weight and increase stiffness. On the flip side, some people report more creaking with press-fit designs.

Many press fit standards are used by different frame and component manufacturers, and they’re not interchangeable.

For example, a Shimano Ultegra Hollowtech II press-fit bottom bracket will fit into an 86.5mm-wide bottom bracket shell and will work with a 24mm-diameter chainset spindle, while an SRAM DUB 92mm press-fit bottom bracket is for mountain bikes with an 89.5/92mm bottom bracket shell width and an SRAM DUB 29mm spindle. You need to make sure that you replace like with like.

This will require a unique tool specific to the type of bottom bracket system used.

The B'Twin Internal Bottom Bracket Removal Tool has 20 teeth to work with many of the most common cartridge bottom bracket designs, for instance. B'Twin's Hollowtech II Bottom Bracket Tool is for Shimano Hollowtech II external bottom brackets and others that use the identical 16 external notches, such as many from SRAM.

Most threaded bottom brackets use an English thread. This means that the non-drive side loosens anticlockwise, as usual, but the drive side loosens clockwise, opposite to usual. Many external bottom brackets have arrows printed to remind you of this.

Make sure you clean your frame's internal threads, and if the threads of your new bottom bracket don't have dry thread locker applied, add an anti-seize compound or something like B'Twin's Teflon Bike Grease. Then tighten your bottom bracket in place according to the manufacturer's instructions.

If you're not an experienced mechanic and you need to replace a press-fit bottom bracket from your frame, we'd suggest getting a professional – such as one of our in-store mechanics – to do the job with the right tools to avoid damage. It sometimes requires a lot of force!