> BTW If you have an alloy shell you don't want very low gears on an FM
> unless you are a lightweight or a bit underpowered. The low gear
> pawls work in slots cut into the shell, unlike the AW/FW/S5 where are
> ramps in a continuous
> band. http://bikesmithdesign.com/
> steel shell adequately supports these (for lack of a better word)
> crenellations.
> The old, thin, alloy shells flex enough that the pawls can bust these
> off <http://bikesmithdesign.com/SA/fm-alloy-oop
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Left-hand cups for F.M. gears were made in at least three patterns, an d the earliest of these had ramped ratchets; ironically, these will usu ally be found in the early steel-shelled models, of course, where they' re needed least, but they'll transfer to the alloy shells without problem - I've done it several times. The fact that the 'crenellated' cups were modified at least once suggest s that S.A. were aware of the problem, but I suppose that they persisted with what must have been obvious to them to be a weakness in the system bec ause it was a bit cheaper to make (neither the first, nor the last, tim e that they did that, of course) - and also a bit lighter, perhaps? Regarding 'hybrid gearing', in my experience the use of 'dished' spro ckets back-to-back will usually work O.K., but I don't think that the lar ger sprockets (which tend to work best) were 'dished'? Also, AFAIK, the se sprockets were only made for 1/8" chain and will not 'work' with 3/32" c hain - unless they're 'skimmed down', of course. If you're going to use a 1/8" chain, you'll need to be sure that the derailleur mechanism is able to accept this width (most early ones will, obviously) and be careful to choose as 'narrow' a chain as possible (rivet lengths in 1/8" chains seem to vary considerably). All things considered, it's probably best to use an earlier, threade d pattern driver with a couple of 3/32" fixed-wheel sprockets and appropria te spacers - unless you must use an 'un-modified' 1/8" chainwheel, of cou rse. Either way, it'd be wise to use the longer S.A. axle (and maybe add a washer to each side to avoid possible fouling of the seat-stay), to ensur e as good a chain-line as possible and maintain tracking of the cycle. Tony Colegrave, Northiam, East Sussex, U.K.
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