Riders replacing a worn or bent crankset on a 7 or 8-speed bike that uses a square-taper bottom bracket.
The FC-M315-2 is a two-ring mountain bike crankset with 36-22T chainrings, made for 7 and 8-speed drivetrains with HG 8/7/6-speed chains. The arms fit a square-taper bottom bracket, so you need a square-taper cartridge bottom bracket. Shimano recommends the BB-UN101 with an LL123 axle length for 68 or 73 mm threaded shells.
Shimano's HYPERDRIVE system pairs SG-X chainrings with a Wide Link front derailleur and an HG chain to improve chain control, which helps front shifting most in severe off-road conditions. The crank supplies the rings; the derailleur and chain are separate. The chain line is 48.8 mm, and it is designed for 135 mm quick-release or 142 mm thru-axle rear hubs. There is no chain guard option. The FC-M315-B2 is a different crank with a wider chain line, so check the model name if you are matching your frame.
36-22T, two rings
A 22T inner ring gives a low gear for climbing, with a 36T outer ring for flatter riding.
For 7 and 8-speed
Shimano lists 8/7-speed compatibility with HG 8/7/6-speed chains.
HYPERDRIVE shifting
SG-X chainrings and the HYPERDRIVE system are designed for consistent front shifting off-road.
Square-taper fit
Recommended bottom bracket is the BB-UN101 (LL123) for 68 or 73 mm threaded shells.
Drivetrain
Fit and build
Great for
Maybe not for
175 mm arms with a 36-22T chainring set. This model is also made with 170 mm arms. It needs a square-taper bottom bracket, and Shimano recommends BB-UN101 (LL123) for 68 or 73 mm threaded shells.
FC-M315-2 or FC-M315-B2?
Shimano makes two versions. This FC-M315-2 has a 48.8 mm chain line and suits 135 mm quick-release or 142 mm thru-axle rear hubs. The FC-M315-B2 has a 51.8 mm chain line for 141 mm quick-release or 148 mm thru-axle hubs. Check your frame's rear hub spacing before you buy, because the chain line is different.
