BMX Bottom Bracket Types

What is a bottom bracket?

A BMX bottom bracket is the bearing system housed in the frame’s bottom bracket shell that allows the crank spindle to spin smoothly. It’s a critical component because it connects the crank arms and pedals to the bike, transferring your pedaling power into forward motion. Different bottom bracket types are designed to fit specific frame and crank setups, and using the correct type ensures proper fit, durability, and performance.

Types of BMX Bottom Brackets

The most common BMX bottom bracket styles today are Mid and American.

Mid bottom brackets are the current standard in freestyle and commonly used in racing. This style uses sealed bearings that press directly in to the frame, leaving a flush fit. This is what the majority of aftermarket frames and mid to higher-end complete bikes use.

American bottom brackets are a larger diameter and can use sealed or unsealed bearings. Sealed American BB's use the same bearings as a Mid BB, but they include a cup that must be pressed in to the frame for the bearings to sit in. Usually entry-level complete bikes use an unsealed American BB, the next step up is a sealed American BB, then mid-level and up bikes will begin using Mid BB's.

Spanish bottom brackets aren't too common these days as the BMX industry sort of settled on Mid being the standard. Spanish BB's work the same as Mid, they just use a slightly smaller diameter.

European (Euro) bottom brackets are primarily used in BMX racing and dirt jump MTB (slopestyle). Euro BB's use cups that thread in to the frame. These cups house the bearings.

I know my style, now what size?

Freestyle

The next step is to determine the spindle size of the cranks. In freestyle BMX, the most common bottom bracket spindle sizes are 19mm and 22mm. 19mm is the standard, especially on complete bikes. 22mm spindles have become more popular in recent years as they offer a bit more durability without jeopardizing weight.

24mm spindles exist, but the industry has sort of settled on 19mm & 22mm being the sweet spot.

Racing

BMX racing has a lot more options when it comes to spindle size. While 19mm is used here as well (and 22mm occasionally), 24mm is considered the standard. But it doesn't stop there! Some brands are using 30mm and even 35mm spindle options! A lot of Mini race bikes use Square Tapered spindles.

We won't dive into the pros and cons of those options here. That is a decision to be made when selecting cranks. When selecting a BB, you just need to know what will work with the cranks you have.

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