Condensed Answer: Modern SRAM GXP bottom brackets are designed for spindles with different diameters on the drive and non-drive side. Consequently, GXP bottom brackets aren’t compatible with Shimano cranks.
SRAM DUB bottom brackets are designed for spindles of a larger diameter and cannot be coupled with Shimano cranks either.
Square taper SRAM bottom brackets, on the other hand, are compatible with Shimano cranks.
Bottom Brackets With External Bearings
The bottom bracket is a system of bearings and cups threaded or pressed into the bottom bracket shell of the bike’s frame.
The function of the bottom bracket is to allow smooth rotation of the cranks.
The cranks are the “levers” through which the rider transmits force to the chainring.
Modern bottom brackets have external bearings sitting outside of the bottom bracket shell.
The benefits of bottom brackets with external bearings are:
- Unrestricted size of the bearings. Since the bearings of the bottom bracket are sitting outside of the shell, they can be much larger than those of bottom brackets with internal bearings. Larger bearings are associated with longevity.
- Spindles of greater diameters. The external bearings make it possible to install large diameter spindles. Larger hollow spindles are stiff, strong and light.
SRAM GXP Bottom Bracket
SRAM GXP bottom brackets are built for a spindle that’s 24mm on the drive side and 22mm on the non-drive side. Meanwhile, modern Shimano cranks have a spindle with a 24mm diameter on both sides.
Consequently, a Shimano crank cannot fit through the non-drive side of a SRAM GXP bottom bracket.
FAQ: Can I replace the spindle of the cranks with one that’s 24/22mm?
Cranks designed for bottom brackets with external bearings come with a spindle that’s press-fitted into the drive-side crank. Therefore, it’s not possible to replace the original spindle.
SRAM DUB Bottom Brackets
SRAM DUB bottom brackets aren’t compatible with Shimano cranks either. DUB bottom brackets are designed for a 28.9mm spindle. And since Shimano cranks rely on a 24mm spindle, a combination of the two results in a non-secure fit.
SRAM Square Taper Bottom Brackets
Square taper bottom brackets are internal bearing bottom brackets found on entry-level bicycles. Their name comes from the square shape of the spindle.
Square taper bottom brackets are often disregarded, but they have always been an affordable option offering satisfactory performance.
SRAM square taper bottom brackets can operate with Shimano’s square taper cranks. Thus, if the bottom bracket is compatible with the frame, you will be able to use Shimano square taper cranks.
That said, the type of the crank should correspond to the bike model. Or in other words, you need road cranks for a road bike and MTB cranks for MTBs and hybrids.
To learn why it’s not recommended to use road cranks on an MTB, consider reading this post.
Since it’s not possible to combine Shimano cranks designed for external bottom brackets with a SRAM bottom bracket, either the bottom bracket or the cranks will have to be replaced.
Option 1: New cranks
The first option is to get SRAM cranks compatible with the bottom bracket in question. The benefit of this approach is that it doesn’t require the removal of the old bottom bracket. The downside is that it’s an expensive solution.
Option 2: New bottom bracket
The other approach is to get a new Shimano bottom bracket compatible with the frame and the cranks. The advantage of this choice is that a bottom bracket is cheaper than a set of quality cranks.
The con is that you will have to remove the old bottom bracket and install a new one. If you pay a bike shop to perform the conversion and install the cranks, the final bill could be relatively high in comparison to the bike’s value.
Thus, you will truly save money only if you do the work yourself. The two procedures aren’t incredibly complicated and can be done by most riders with a bit of help.
It will also be necessary to get additional tools (e.g., a bottom bracket spanner, a bottom bracket press) to complete the mission. The price of the instruments has to be factored in too.
Note: Make sure that the new and the old bottom bracket attach to the frame the same way. If the bottom bracket is threaded, the new one should be too. If it’s press-fitted, the new one should rely on the same retention method.