BMX Bottom Brackets

BMX Bottom Brackets: Essential Components for Your BMX

In a BMX bike, the bottom bracket is located in the frame at the intersection of the crank arms. This section of the bike frame is known as the bottom bracket shell. The primary components here are two bearings and spacers, designed to enable smooth pedal motion for speed gain. Built to be exceptionally strong and sturdy, these parts must endure significant stress from vigorous pedaling.

Varieties of BMX Bottom Brackets

There are four main styles: American bottom bracket (51 mm), mid bottom bracket (41 mm), Spanish bottom bracket (37 mm), and euro bottom bracket (35 mm threaded). These styles differ in size, with the measurements indicating the bearing's outer diameter required for your frame.

The American bottom brackets, the earliest design, feature the largest diameter and include either sealed or open bearings in cups. Most contemporary BMX bikes use mid bottom brackets due to their easy installation and flush fit within the frame. Spanish bottom brackets, being lightweight and compact, offer a sleek appearance and are pressed into the frame. Euro bottom brackets are typical in race BMX bikes and are installed with threads, having the bearings in cups.

Determining the Appropriate BMX Bottom Bracket Size

Beyond selecting the type, ensuring the correct bottom bracket size for your crank axle is crucial. Bottom brackets are available in inner diameters of 19 mm, 22 mm, and 24 mm, referring to the spindle size fitting through the bearing. The 19 mm axles are most prevalent, with nearly all brands providing models in this size. The 22 mm and 24 mm axles offer enhanced strength without added weight compared to the 19 mm.

If you're uncertain about which bottom bracket to select, focus on compatibility with both the design and spindle size of your current setup. For instance, if your frame is designed for a euro bottom bracket and your cranks use a 22 mm axle, you'll need a euro 22 mm bottom bracket.

If a new crankset is also on your list, explore our selection of BMX Cranksets.