Overview and Specifications of WheelTop's Affordable Electronic Groupset "EDS"
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How to Identify Bottom Bracket (BB) Types and Choose Replacement Parts for Road and MTB Bikes
Posted at: Feb 29, 2024
Among road and MTB bike components, bottom brackets (BBs) can be especially difficult to match with replacement parts. This article explains how to identify BB types and how to choose the right replacement parts.
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Types of Bottom Brackets for Road Bikes and MTBs
There are many types of bottom brackets (BBs) used in performance bicycles. Each manufacturer proposes what they consider the optimal standard based on strength, cost, stiffness, and other design factors. As a result, a surprisingly wide variety of BB standards exist, driven by differing design philosophies across brands.
BB specifications are determined by the combination of:
- Mounting standard
- BB shell width
- BB shell inner diameter
- Crank spindle width
- Crank spindle diameter
It’s common for not just brands, but even different bike models from the same brand to use different BB standards.
How to Choose the Right Replacement BB for Your Road Bike or MTB
To choose the right replacement bottom bracket, the first step is to identify which BB standard your bike uses.
Check Which BB Standard Your Bike Supports
Most manufacturers list the BB specification on the official product page for your bike. So your first step should be to check the manufacturer’s website.
If no information is available online, or if your bike model is no longer listed, you can remove the current bottom bracket and search for its specifications using the model number printed on it.
For example, if the BB has “SM-BB93” written on it, you can search that term to find Shimano’s official documentation for the “XTR Threaded Bottom Bracket.”
If you’re still unable to find specific specs using the above methods, try measuring the following:
- Mounting standard – Is it threaded or press-fit?
- BB shell width – Measure the frame’s BB shell width with the BB removed
- BB shell inner diameter – Measure the internal diameter of the frame’s BB shell
For example, if it’s (1) press-fit, with (2) a shell width of 89.5mm and (3) an inner diameter of 42mm, that indicates the BB92 (PF92) standard, commonly used by Shimano and others.
Find a Bottom Bracket Based on “BB Standard x Crank Standard”
The previously mentioned BB standard refers to the type that fits your bike’s frame (BB shell). However, in practice, you also need to attach a crankset to the BB, which means you must find a bottom bracket compatible with your chosen crank.
For example, if you want to upgrade to a Shimano Hollowtech II road crankset, you’ll need a BB that is both compatible with Hollowtech II and fits your road bike or MTB’s BB shell.
One thing to watch out for is that even within the same brand, not all standards are compatible. For instance, Shimano’s “Hollowtech II” and “Octalink” cranksets are not interchangeable. Similarly, SRAM’s current “DUB” system and older “GXP” standard are not compatible.
Choosing the Right Replacement BB
Once you’ve determined the BB and crank standards, you can select the appropriate bottom bracket. While BBs are an important component, they are relatively simple in structure. As such, performance differences across product grades are often minimal. So it’s usually fine to choose a model that fits your budget.
One key point to consider is the required tools. Different BB types require different tools for installation. Without the correct tool, you may not be able to install the BB—or worse, you could damage the components. Always use the recommended tools for the job.
What If There’s No Compatible BB?
When replacing the BB on an older bike or installing a crankset that’s not supported by the original BB, you might face the problem of “no compatible BB available.”
This is where third-party manufacturers that specialize in bottom brackets can be incredibly helpful.
Two highly respected brands from Taiwan—both cycling powerhouses—are TOKEN and WISHBONE.
TOKEN is widely available in the domestic market and is carried by many bike shops that specialize in performance bikes. In addition to BBs, TOKEN is also known for producing affordable yet high-performance wheels.
TOKEN offers customizable BBs that support various shell widths and spindle diameters, so it’s a good place to start your search:
WISHBONE is known for offering an extensive range of BBs capable of handling highly specific fitments. If you can’t find a compatible BB here, it’s safe to say it probably doesn’t exist:
Both brands are significantly more expensive than Shimano’s OEM BBs. However, the benefits include high-quality construction and, most importantly, the ability to find a BB that fits your MTB perfectly.