Ted - I value your experience and your friendship very highly, but I think you may be overly conservative on using a FW on a fixed gear hub. Here's my reasoning:
1) if the number of threads were really the issue, the FW would obviously be as conservative as a fixed cog - the FW certainly will engage all the hub threads, and then some.
2) The force that the cog puts on the hub depends on the kind of contact between them. This includes the thread length and area, and the butt surface on the hub flange extension. I think that the key issue is actually the thread match, not having an English on French hub. If you're very conservative, not mixing Italian (55 degree included angle) with English (60 degree). I've once stripped an aluminum hub, but it was the oversized lockring on a worn locking portion, not the cog itself.
3)The other key factor is the force exerted by the rider. The bigger the gear, the less force exerted. So, if you're conservative, you won't use a FW with more teeth than you'd ride on a fixed cog. This is the reason Sheldon suggested that you could protect your ASC by riding in a bit higher gears: less force on the guts of the box.
Now, I could be wrong, and I'm not gonna offer to replace hubs that others damage, but this is one thing that hasn't worried me a great deal. Maybe just because I'm not as strong as I used to be (or would like to believe that I used to be).
harvey sachs mcLean va USA
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I was going to respond and forgot. Here's my take:
One always takes a chance when putting a freewheel albeit a single on the
narrow track hub thread section.
Chances are it will be OK, but an aluminum hub is risky and a steel hub
mght
be OK.
Personally I wouldn't do it.
The thread stress from the freewheel might be just too much for the hub to
hold especially under hard riding, and you may ruin a hard to replace
treasured hub.
You takes your chances. A 3/4/5 speed freewheel, hub suicide, a single
freewheel, chancy, especially on an alloy hub.
Not on any of my bikes on my watch, neither a recommendation.
Ted Ernst
Palos Verdes Estates
California, USA
>> No problems at all. Go for it!!
>>
>> Jeff Wybrow
>> Melbourne, Victoria, Australia