The XTR SM-BB93 sits at the top of Shimano's threaded mountain bottom bracket line, and the case for spending up over an XT or SLX unit comes down to two things—the sealing package and the bearings themselves. Shimano redesigned this generation around smaller-diameter bearings paired with a reworked seal system, which shaved roughly 19 grams versus the outgoing M980-era unit and, according to Shimano's own testing, cut rotational friction meaningfully compared to the previous XTR bottom bracket. For a threaded, steel-bearing bottom bracket without any ceramic upcharge, 73 grams is where that spec chase lands.

The interface is standard Hollowtech II—24mm spindle, external cups that thread into a BSA/English shell. Three 2.5mm spacers come in the box so you can set it up for either a 68mm or 73mm shell, which covers the vast majority of hardtails and full-suspension frames still running threaded bottom brackets. If your frame is press-fit, this isn't the part; the BB93 is threaded only. The cups and sleeves are anodized black, which holds up better than raw aluminum against the trail spray and drivetrain grime that ends up living down there.

Compatibility spans the full Shimano MTB Hollowtech II era: XTR FC-M980 through the current M9100 and M9120/M9130 cranks, plus FC-MT900, and it works equally well with XT, SLX, and Deore cranks running the same 24mm spindle. Third-party mountain cranks built to the Hollowtech II 24mm standard—Race Face, FSA, and similar—install the same way. If you're running a mid-tier crankset but want the XTR bearing and seal package where friction actually costs you watts, this is the straightforward upgrade path without touching the crank.... Read More