David- The gap between the chain lifting off the smallest cog and the inside of the seat stay end is a must to avoid a nasty nick in the stay end. The minimal dimension from the hub's free wheel seating face to the axle's locknut will vary due to a few factors. (And the hub presets the seat face to flange dimension). Of course the cog count is the biggest part. But when getting down to the last few mm's the small cog diameter/tooth count and the stay's end relief (if any) are the real limiting factors. A 14 tooth small cog with a non relieved stay end can need 2 or 3mm more then a 13 tooth cog with a nicely profiled inner stay end.
> Actually, you really don't need 126mm to run 6-speeds and still have
> reasonable wheel dish.
>
> Most 6-speed production bikes showed a curious lack of precision in that
> the outer face of the smallest cog was not close to the ~3.3mm minimum of
> space needed between cog and dropout. Result was that one could easily
> remove 2mm from both ends of the wheel's axle spacers (down to 122mm!) and
> still have all the clearance needed, especially once a modern, narrow
> chain is substituted (just don't use a 14t small cog, on certain frames
> that will have the chain hitting the end of the seatstay during the last
> shift).
> So, a modestly-dished wheel measuring 122mm (easily slid into any 120mm
> frame) should easily accomodate a 6-speed Shimano UG freewheel. All that
> is needed is a bit of fine-tuning to the axle (and any freewheel) spacers,
> all part of a reasonably well-built, purpose-built wheel. This isn't
> radical at all! Just look at the huge amount of wasted space that many
> 5-speed freewheel-equipped bikes left unused: enough to throw your chain
> to the axle!
>
> David Snyder
> Auburn, CA usa
>
>
> ----- Original Message -----
> From: "Thomas Adams" <thomasthomasa@yahoo.com>
>
> Subject: Re: [CR] Freewheel re-spacing
>
>
> Dear Don and List:
>
> Yeah, you can re-space a 120mm to 126mm, but is it morally right?
> Especially with really old frames, which never would have been available
> in 126mm rear spacing.
> _______________________________________________
Andrew R Stewart
Rochester, NY