Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
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That type of hub is supported on bearings at either end. The freehub bolt serves to make the hub/freehub combination into a single rigid module. Picture if you lay a pencil between 2 supports. It rests straight across, and if you push down in the middle, it'll flex a bit but that's all.
Now imagine that you took a pencil, removed the eraser, and pushed the end onto the eraser of another pencil, making a single double ended pencil joined by the eraser. Lay that across 2 supports, and at the lightest touch it'll sag in the middle, if you push harder it'll come apart at the eraser. The only way to make it rigid is to splint it across the connection with something like a piece of rigid tubing, so it acts like the first pencil did.
Likewise your hub, The bearings hold the freehub spline into the hub so it can't come out. But as the chain tugs on the cassette, especially on the larger inboard sprockets, the hub and freehub will deflect at the non-rigid joint, and since they're turning it'll cause wear there. Having it properly tightened prevents that deflection and wear preserving the integrity of the joint.
Note, that if you rode any distance o rode hard long enough, the steel freehub doesn't suffer, the aluminum hub shell does, and since it includes the wheel it can be an expensive problem.
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Last edited by FBinNY; 09-11-12 at 05:57 PM.