BMX Bottom Brackets

Crucial Role of BMX Bottom Brackets

Within the structure of a BMX bike, the bottom bracket is situated in the frame where the crank arms converge. This section of the bike frame is known as the bottom bracket shell. It consists primarily of two bearings and spacers, which enable the rider to rotate the pedals effortlessly to gain speed. The components are exceptionally robust and durable, designed to endure the significant force produced by intense pedalling.

Varieties of BMX Bottom Brackets

The four principal varieties include the American bottom bracket (51 mm), mid bottom bracket (41 mm), Spanish bottom bracket (37 mm), and euro bottom bracket (35 mm threaded). These variants have different dimensions, with the numbers indicating the outer diameter of the bearing necessary to fit your frame.

American bottom brackets are the oldest type, recognised by their large diameter. They feature either sealed or open bearings that rest in cups. Mid bottom brackets are common on most modern BMX bikes due to their easy installation and snug fit within the frame. Spanish bottom brackets, being compact and lightweight, offer a streamlined appearance and are pressed into the frame rather than being screwed. Euro bottom brackets are typically found on race BMX bikes, where they are screwed into the frame with bearings housed in cups.

Determining the Correct Size for a BMX Bottom Bracket

In addition to the type, having the correct size of bottom bracket is essential for compatibility with your crank axle. The varied inner diameters include 19 mm, 22 mm, and 24 mm, which correspond to the spindle size that fits through the bearing. The 19 mm axles are the most prevalent, with nearly all brands offering models in this size. The 22 mm and 24 mm axles are thicker and more robust than the 19 mm and often carry no extra weight.

If uncertainty persists over the required bottom bracket, it is crucial to ensure both the style and spindle size align with your existing arrangement. For instance, if your frame accommodates a euro bottom bracket and your cranks use a 22 mm axle, a euro 22 mm bottom bracket will be necessary.

If you're also in the market for a crankset to pair with your new bottom bracket, take a look at BMX Cranksets.