Why does only Shimano make hollow cranks? And are hollow cranks better than non-hollow ones?
IIRC Shimano have a very clever patent coveing the hollow forgeing process.
Cannondale and Crank brothers both made CNC’d cranks which are/were glued together and incedibly light. Rotor do it by drilling down the center of the crank. The important bit with Shimano though is they’re forged hollow, not CNC’d, which makes them much tougher, which is why DH’ers will happily use XTR cranks which only weigh a smidgen more than some silly light XC offerings with weight and usage limiets.
I remember a story that even NASA went to Shimano to see how they do it and it’s a very closely guarded patent, think about stuff like the suspension arms in your car (or at least sports/super cars), they’d be an ideal application, or even the con-rods in the engine.