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I'm wondering how the load (or weight) of the bike is transferred to the cartridge bearings in the hub with a through-axle setup. Initially I thought that it is the through-axle that transfers the load from the fork (in case of a front hub) to the bearings. Given how easily the through-axle fits in the hub, I was wondering how fretting of the through-axle against the inner bearing race was not a problem with so much clearance (e.g. not a press-fit as is common with ball bearings).

But after reading https://www.mtbr.com/threads/explain-through-axles-to-me.1178078/, it seems that the weight is indeed not supported or transferred by the through-axle itself, but in some other way that I didn't really get from that discussion, and that the through axle only serves to clamp the whole thing together? I'm confused though, what exactly supports the weight from the bike put on the wheel and how is it transferred to the bearings?

I'm mainly trying to understand because I'm trying to design a quadricycle and seeing if I can use the same catridge bearings to support the rear axle, and use through-axle hubs (with cartridge bearings) on the wheels in a single-side mounted fashion (and just clamped on the other side).

Is there anyone that can provide a clearer answer that the linked discussion? Thank you!

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There are two ways, depending on the type of the hub.

Most hubs use a separate axle around the thru-axle. So for example if you have a 15mm thru axle in the front, you would have a 18mm axle around the thru axle. The thru axle only tightens the other axle to the fork. Load is mainly carried by the other axle. Then the 18mm inner diameter bearing gets the load via the other axle.

However, some hubs (for example Novatec D201SB fatbike hub) use the thru axle itself to carry the load. In this case, there would be a 15mm inner diameter bearing around the 15mm thru axle. The bearings get the load directly from the thru axle.

Relevant YouTube video:

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  • Thank you, that's exactly what I wanted to know!
    – bwindels
    Jul 8 at 7:38

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