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This might have an obvious answer but when I look at freehub designs, I always see the pawls on the inner member and ratchets on the outer member. Here is an example:

Freehub

Has anyone ever reversed that configuration so that the ratchets are on the inner member and the pawls & springs on the outer member? If not, what are the flaws of such a design?

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    Centripetal force acts to increase engagement pressure in this design, but without knowing the mass of the pawls and the spring stiffness I can't know whether it's significant. I suspect not. – Chris H Mar 9 '17 at 20:52
  • It would also vary depending on the rpm and make it hard to rely on it. But it is still a plus in order to engage them – Shinagan Mar 9 '17 at 21:25
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    The outer side provides a large surface to create the ratchets such that there can be more and stronger ratchets compared to the reversed design. Many ratchets are desirable to minimise the angle before the hub engages. – Christian Lindig Mar 9 '17 at 21:49
  • @Shinagan I was thinking more of not making the engagement worse, rather than making it better, but you're right – Chris H Mar 9 '17 at 22:13
  • If the ratchet surface were the inner surface then the outer pawl assembly would have to be about 3 times as thick as the ratchet "cup" you see above. This would make the area of the ratchet piece smaller, and would mean that it would have to withstand more force for a given amount of torque. – Daniel R Hicks Mar 9 '17 at 23:10
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I am going to combine the comments into an answer - feel free to improve.

The main benefit is the larger circumference of the ratchet surface.

This means for the same torque on the wheel, there is less total force on the ratchets holding the freewheel. It also means there is room for more pawls, meaning less force on each individual ratchet. This allows smaller ratchets and pawls, meaning you can have more of them, meaning even less force.

Additionally smaller ratchets and pawls allow smaller angles before engagement of pawls locking the free hub - less slop when starting to pedal after free wheeling. The smaller angle before pawls engage also means the pedals have less time to accelerate - meaning the forces and wear and tear on the engaging pawls are lower.

Having more pawls means the freewheel is more likely to operate if one fails to engage.

Conversely, a smaller diameter ratchet would be able to support fewer pawls, which would have to be much stronger or likely to be less reliable and engage less quickly when pedaling is resumed after freewheeling

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A number of BMX companies have done it over the years starting, I believe, with Wethepeople. It's called the q-lite system. enter image description here

I've always heard great things about it but never tried it.

  • Of course, it may be that you've heard great things about it because it's a generally well-made product, rather than specifically because the pawls are on the outside. – David Richerby Mar 10 '17 at 14:46
  • @DavidRicherby That is probably the case but pretty much all of the weird concepts that failed in BMX were quite well made too. – Philip Gibbons Mar 10 '17 at 16:35
  • This is very interesting, that is the kind of system I was looking for at first and I am pleased to see that a company is actually selling it! Thanks! – Shinagan Mar 10 '17 at 21:37

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