BMX Bottom Brackets Are the Core of Your BMX

On a BMX bike, the bottom bracket is installed in the frame where the crank arms meet. This part of the bike frame is called the bottom bracket shell. The main components are 2 bearings and spacers, which allow the rider to spin the pedals freely to gain speed. These parts are extra strong and sturdy to withstand the pressure created by aggressive pedaling.

The Different Types of BMX Bottom Brackets

The four main types are: American bottom bracket (51 mm), mid bottom bracket (41 mm), Spanish bottom bracket (37 mm), and euro bottom bracket (35 mm threaded). These sizes refer to the outer diameter of the bearing required to fit your frame.

American bottom brackets are the oldest type and have the largest diameter. They come with either sealed or open bearings that sit in cups. Mid bottom brackets are common on most BMX bikes today due to their simple installation and snug fit in the frame. Spanish bottom brackets are small and lightweight, offering a clean look and are pressed into the frame rather than threaded. Euro bottom brackets are typically found on race BMX bikes and are threaded into the frame with bearings sitting in cups.

What Size Bottom Bracket Do I Need for BMX?

Besides the type of bottom bracket, it's crucial to have the correct size to fit your crank axle. The different inner diameters of bottom brackets are 19 mm, 22 mm, and 24 mm. These measurements refer to the spindle size that goes through the bearing. 19 mm axles are the most common, and nearly all brands offer models of this size. 22 mm and 24 mm axles are thicker and stronger than the 19 mm ones and usually add no extra weight.

If you're still unsure about the bottom bracket you need, the key is to ensure both the style and spindle size are compatible with your existing setup. For instance, if your frame supports a euro bottom bracket and your cranks have a 22 mm axle, you'll need a euro 22 mm bottom bracket.

If you are also looking for a crankset to go with your new bottom bracket, check out BMX Cranksets.