Shimano SLX M7100 crank is the lowest-tier crank using Shimano’s top-level manufacturing technology and comes in a swish gunmetal blue or black colourway
Shimano SLX M7100 crank axle is hollow steel and 24mm diameter. This is slimmer than most other brands, but Shimano claims multiple benefits, including improved torsional stiffness (against twisting), less rotational friction as the axle rotates inside the bearings, plus the ability for an outboard bottom bracket design. The latter leaves sufficient space for bigger and (in theory) more durable bearings and seals, and has a wider bearing stance to increase rigidity and pedal efficiency. The first claim on bearing size relative to axle sounds about right to us, but almost all other brands have a similarly wide bearing stance nowadays.
It might be mid-range in terms of price, but still uses the top Hollowtech II construction mentioned, whereby the forged alloy arms are hollow to save weight and use a multi-splined axle integrated into the driveside crank. The exact process of bonding and forging is a closely guarded secret by the Japanese firm.
Shimano’s HollowTech 2 system fastens with a double Allen pinch bolt on the left crank, with an extra security measure of a little plastic spacer to prevent the crank coming off in the unlikely event of it working itself loose.
Latest-generation SLX ditches a built-in spider for direct-mount chainrings, and at this price that means aluminium arms and steel teeth. The sprocket uses Shimano’s DCE+ (Dynamic Tooth Engagement) layout, which is really just a variant on the widely-used thick/thin design. The brand’s latest profile has some slight angles on alternate teeth, works fine and is leagues ahead of the earlier DCE design that suffered with awful chain suck in certain kinds of UK grit.
With a chainring, the total SLX cost and weight is almost identical to SRAM GX Eagle. Both cranks perform brilliantly, and both are recommended. SRAM’s X-Sync 2 chainring has a more sophisticated tooth profile that runs a fraction smoother in grit and grime, but latest-generation Shimano SLX M7100 crank arms are a tiny bit lighter.