Faced with numerous bottom bracket models and standards, you can follow these clear steps to confidently select the correct bottom bracket for your beloved bike.
• Step 1: Determine Your Bike Frame's Bottom Bracket Standard
This is the most fundamental and critical step. You need to identify the type (e.g., threaded or press-fit), width, and inner diameter of your bike frame's bottom bracket shell.• Type: The most common is British threaded (BSA), with variants like BSA24, BSA-DUB, BSA30, and T47-24 bottom bracket. There are also various Press-Fit standards, such as BB86, BB92, BB30, and PF30 bottom bracket, as well as the Italian threaded (ITA) standard, e.g., ITA-24 and ITA-30.• Measurement: Obtain the precise shell width and inner diameter through measurement. If the frame's standard isn't marked, the most reliable method is to remove the old bottom bracket and measure the shell's width and inner diameter directly. For example, British threaded shells are typically 68mm or 73mm wide.The press-fit diameter of the BB86/BB92 (some manufacturers also call it PF4124) is 41mm, so it is important to note that the inner diameter of the bottom bracket shell must also be 41mm.
• Step 2: Confirm the axis specifications of the bicycle chainring (crank)
The bottom bracket is the "adapter interface" connecting the bicycle frame to the bicycle crankset and must match the crankset's axle.• Common Axle Diameters: For example Shimano and its compatible cranksets typically use a 24mm axle. SRAM GXP uses a 24mm axle (drive-side) / 22mm axle (non-drive-side). BB30 and many FSA cranksets use a 30mm axle. Additionally, SRAM DUB cranksets use a 28.99mm axle (often simplified to 29mm by manufacturers).• Integrated vs. Square Taper: Most modern bicycle cranksets use an integrated design (where the axle is integrated with the crank arms). When selecting a bottom bracket, you only need to focus on the crankset's axle diameter.
• Step 3: Understand Compatibility and "Adapter" Concept
If your bicycle frame and crankset follow different standards, don't worry. Compatibility can usually be achieved through an "adapter bottom bracket."• Core Tool: You can refer to the lookup logic provided in the table from our previous article: the horizontal axis represents the frame's bottom bracket standard, and the vertical axis represents the crankset's axle. The intersection point indicates the bottom bracket type you need.• Typical Example: Want to install a BB386 crankset (with a 30mm axle) onto an English threaded (BSA) frame? You need a "BSA30" specification bottom bracket (i.e., a shell with BSA threads and internal bearings that support a 30mm axle).
• Step 4: Pay attention to other small installation details.• Bottom Bracket Length (For Square Taper/ISIS Only): For older square hole or splined bottom brackets, the spindle length is crucial. It directly affects the chainline—the alignment of the chain with the cassette sprockets after the crankset is installed. The goal is to ensure a straight chain line; otherwise, issues like chain drop may occur.• Use of Spacers: Many external bearing bottom brackets (e.g., Shimano Hollowtech II, SENICX, KACTUS TECH) come with spacers for fine-tuning the crank position on different shell widths and preloading the bearings.Spacers and spacers quantity must be installed according to the shell width, crankset type, and specific requirements. Note: Not all installations require spacers. The image below shows what these spacers look like. For instance, the MTOMSEE store provides spacers with their bottom brackets tailored to different installation scenarios; the specific quantity and dimensions are subject to what you receive in the package.
Published by www.goodbike.cn. If you have any questions,we welcome your inquiries and discussions.
