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Background I have an 8 speed 26" freehub/cassette based wheel on my MTB. It runs a 7 speed MTB cassette with a spacer and 7 speed shifter. It works fine.

I also own a 20" folding bike that has a 6 speed freewheel. I wish to increase the gear range from the current 14-28 freewheel to both larger and smaller. However 6speed freewheels are expensive and only available in 14-28 or very similar ranges.

I also have a loose hub with a 7 speed freehub.

My plan is to put the 7 speed hub onto the MTB and use the 8 speed hub on the folder, with a new wide-range MTB cassette like an 11-32 or 11-34 and a new 8 speed shifter.

I understand that the folder's 20" wheel needs a complete rebuild onto a cassette-based freehub hub.

Question Do I have to take the 8 speed hub from the MTB wheel (meaning two complete wheel rebuilds) or can I swap the 7 and 8 speed freehub bodies off the hub, which will mean only one wheel rebuild ?

Similar to Can I replace a 9spd freehub with a 7spd one? but not quite the same

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Cheap 14-34 Shimano 6spd freewheels are still being made.

As for freehub body swapping, there are a couple things at play. One is the compatibility issues with swapping freehubs at all, and the second is issues related to hub spacing, axle spacing, and wheel dishing with making the swap in question if it is possible.

Across manufacturers, there is no real freehub swap compatibility (barring cases where two different OEMs use the same Joytech hub etc). Within manufacturers there can be some. Many Shimano hubs use the same spline pattern and dimensions at the interface between shell and freehub body, and can have freehubs interchanged. Many of the common 8/9/10 Shimano freehub bodies are very close to dimensionally the same. (One sticky point here is that they can look dimensionally identical but usually need their cone/dust seal/spacers etc to be that of the hub they came from. You should assume that's the case unless you want to play games making it work right.)

That said, there are a couple exceptions to this within Shimano (completely different shell/freehub body interfaces), and 7 speed hubs are where at least one I know of can be found. So even if both freehubs in question are Shimano, it depends on the specific hubs models.

Secondly, if both are interchangeable Shimano freehub bodies, 7-speed freehub bodies are shorter, so to get the spacing back to where you started on the MTB wheel you'll have to add spacers on the left side and then re-dish the wheel. (I recommend doing it this way, because then you get more total spoke tension. You don't get all the strength benefits of a 7-speed hub because it will still have the flange spacing of an 8-speed hub.) And then on the folder hub, you'll need a longer axle.

Also I should note that just respacing the folder's existing rear wheel to 7-speed, swapping axles if needed, and then redishing it is another possible course here.

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  • Thank you for the freewheel link - that meets half the need, but the other part; higher top gearing remains. Apparently 13 tooth minimum freewheels exist but they're rare and expensive, whereas moving to a cassette gives me options down to 11 tooth for quite cheap. – Criggie Aug 20 '16 at 5:04
  • One hub is a shimano FH-RD30 (lowest spec) which is the 7 speed. This is not in a wheel. The other is an unbranded 8 speed hub mounted in the 26" wheel. I'd try swapping, but removing the freehub body from the bare hub will require a lot of torque, hard to do without the leverage of an attached rim. – Criggie Aug 20 '16 at 21:00
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    I don't recall seeing FH-RD30 so I can't comment on what might be hiding in there. But if the 8-speed hub isn't Shimano, there's basically no hope of compatibility. – Nathan Knutson Aug 21 '16 at 6:51
  • OK looks like two wheel rebuilds coming up... More news to come on this one. – Criggie Aug 21 '16 at 6:57

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