BMX Bottom Brackets

BMX Bottom Brackets: The Heart of Your BMX

On a BMX bike, the bottom bracket is located within the frame at the junction of the crank arms. This area of the bike frame is referred to as the bottom bracket shell. It primarily consists of 2 bearings and spacers, allowing the cyclist to spin the pedals effortlessly to gain speed. These components are exceptionally robust to endure the considerable force generated by vigorous pedalling.

Varieties of BMX Bottom Brackets

The four principal types are: American bottom bracket (51 mm), mid bottom bracket (41 mm), Spanish bottom bracket (37 mm), and euro bottom bracket (35 mm threaded). Each varies in size, with the dimensions here indicating the outer diameter of the bearing needed to fit your frame.

American bottom brackets, the oldest type, feature the largest diameter and include either sealed bearings or open bearings positioned in cups. Mid bottom brackets are prevalent in many current BMX bikes due to their ease of installation and seamless fit within the frame. Spanish bottom brackets, being small and low in weight, offer a streamlined appearance and are pressed into the frame, unlike threaded options. Euro bottom brackets, typically seen on racing BMX bikes, are threaded into the frame with the bearings housed in cups.

Determining the Appropriate BMX Bottom Bracket Size

In addition to selecting the correct type, it's essential to choose the right size bottom bracket to match your crank axle. The various inner diameters for bottom brackets are 19 mm, 22 mm, and 24 mm. These sizes correspond to the diameter of the spindle that passes through the bearing. Most brands produce models with 19 mm axles, as they are the most common. Meanwhile, 22 mm and 24 mm axles are more robust than the 19 mm options and are generally not heavier.

If you're still uncertain about which bottom bracket is suitable, the main point is to ensure both the type and spindle size align with your existing setup. For instance, if your frame accommodates a euro bottom bracket and your cranks possess a 22 mm axle, you will require a euro 22 mm bottom bracket.

Should you need a crankset to accompany your new bottom bracket, have a look at BMX Cranksets.