Shimano FH-MT410-B 12-speed Microspline freehub design discussion

[BikeGremlin]

I got a question in this video's comment section:

I've get it about teeth of this freehub, but definitely miss about support on a shaft. I've seen two bearings in body of hub and two in a actual freewheel part. Or problem is that there was fill bearings and than was installed cartlidge bearings so actual fill bearings don't give enough support in stock part?

 

[BikeGremlin]

That is a problem similar to the one I've noticed with DT Swiss cartridge bearing freehubs (and most other cartridge bearing rear hubs I've worked with). The video discussing the problem in detail (with some sketches, photos, and close-ups):

Briefly put:

The two bearings that hold the freehub serve to keep the freehub spinning smoothly, and the freehub leans over them against the axle when you apply the pedalling torque.

However, when you just ride and hit a bump, or jump, or similar, all that load is not transferred via the two freehub bearings - but it is in fact transferred via the two leftmost bearings that are pressed into the hub's body. How does that work?

• The axle is held against the frame thanks to the preload created by the "thru-axle" skewer.
• So, when you load/weigh the bicycle, the frame presses against the axle's ends.
• The axle then transfers that load to the hub via the two bearings pressed into the hub itself - the above-mentioned two leftmost bearings (the freehub is basically loosely attached without any direct preload until you press on the pedals with some force and apply some pedalling torque).
• The hub's body then uses the spokes, rim, and the tyre to transfer that load to the ground.

Or vice-versa, if you look at it from the bottom-up direction. Any force equals the same force in the opposite direction (action-reaction).

With cup-and-cone hubs, the bearings are further apart, and the right hand side bearing is right at the end of the axle. That is depicted in the cover photo of the Rear hub article (and explained in the article). With such hubs, the freehub itself also has its own set of bearings that don't transfer the load of the rider's weight (and any road impacts), via very small bearing balls lined up between the freehub and the hub. My video about Machining a Shimano freehub disassembly tool shows what that looks like when disassembled near its start.

It may be counter-intuitive, but, again, the freehub bearings don't transfer the load. That is something that even some great mechanics fail to grasp.

I've tried to demonstrate the freehub's play in the Cassette (& Freewheel) Wobble explained video (that part starts at about 9 minutes, in the "Cassette play" chapter).

Relja