Bruce,
Interesting subject. I've tried a few experiments with
making classic drop-parallagram derailleurs shift wide
ratios better. I installed a long cage from an old
Simplex on a Galli and found it worked well with
wide-ratio freewheels (14-34) only if the front
chainrings were half-stepped. Anything over a 6-tooth
jump on the chainrings and the shifting went south
fast. I had similar results adding a Rally cage to a
NR derailleur. I believe a sprung upper pivot is the
key to making this work very well. The first
generation Rallys work better (in my opinion) than the
'modified-NR type'. The cheap Tourney & Falcon
derailleurs that come on department store bikes
actually shift pretty decent over wide-ratio
freewheels & triple chainrings. If you watch one of
these derailleurs in action, the upper pivot spring
does quite a bit of work taking up chain slack and
maintaining a reasonable chain gap between the jockey
wheel and freewheel. Of course, these cheap
derailleurs don't possess much mojo...........
cheers,
byron morton
nashville, tn
> I am interested in this topic for several reasons
> and
> have several ideas which I haven't tried yet.
>
> 1) I like thumb shifters on my daily commute bike
> which has flat bars. (Not Shimano Rapid Fire and all
> that stuff).
>
> 2) I'd like some adapters that would allow me to
> mount my Campy down tube shifters up on the flat
> bars
> in a friction thumb shifter arrangement.
>
> 3) I don't care either way if they index or are
> infinitly variable. All my index shifters seem to
> want to be cleaned, oiled, and adjusted far too
> often
> to keep them operating properly to suit me so I wind
> up overshifting them most of the time anyway.
>
> 4) I use some Suntour thumb shifters in the friction
> mode but I'd rather use some Campy shifters.
>
> 5) Those variable ratio bell cranks that were talked
> about and shown recently seems like a possible
> solution to get an index shifter to work on an older
> derailleur that was meant for friction shifting. I
> think Simplex made them. But they're nothing
> complicated that couldn't be made up by almost
> anyone.
> With one of those, you could vary the amount of
> travel
> the derailleur moved for each detent of the lever
> without worrying about the diameter of the lever
> barrel or the amount of cable it pulled between
> detents.
>
> 6) As far as lowering the derailleur and running it
> parallel with some long cages... I've made my own
> long cages and they'll take up more chain for a
> third,
> small chainring in the front but won't shift
> anything
> bigger than a 26 tooth in the rear. But maybe using
> a
> longer derailleur hanger would solve that problem
> also.
>
> Bruce Schrader
> San Francisco
>
> =====
> "Not all those that wander are lost."
> -J.R.R. Tolkien (1892-1973)
>
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