Converting to index shifting on a 120mm rear
 

I've asked this C&V and gotten very little useful info. I know, it doesn't adhere to C&V principles but I have reasons to consider it. What options would there be to convert a 5-speed freewheel system to index shifting, preferable without swapping the rear hub?

Here's the way I see it. One click on the lever displaces the cable x amount. That moves the derailleur (let's say the rear) laterally y amount. Actually, y would be x times a property of the derailleur, specifically the ratio of lateral displacement per cable displacement. The cogs are spaced z amount, and as long as y = z it ought to be workable. The trouble is, those values for a variety of freewheels, derailleurs, and indexing levers aren't readily available to me, at least that I know of.

I have at least two options for freewheel, a standard 5-speed or a Suntour Ultra-6. (Re-spacing the frame(s) is not a great option.) I could whatever derailleur and shifters could be made to match either of these freewheels.

Any thoughts? Thanks!

Ain't gonna work. Sounds like you already understand the problem.

Well, in the homework assignment sense I understand the problem but I don't know if there is or isn't a solution. Won't know that for sure until I have those values for available components, old or new.

I have picked up a few five speed indexed thumb shifters that work on Shimano freewheels. I typically find them on crappy older hybrids: Huffys, Roadmasters, etc. I have not seen five speed index DT shifters.

Thumb shifters, or at least something on the bar, is exactly what I'm thinking of. But with what derailleurs?

If they're Shimano-compatible shifters, then Shimano derailleurs. With some rare, unusual exceptions that don't apply here Shimano shifters will index Shimano derailleurs.

FWIW: here's some indexed 5-speed downtube shifters: http://www.biketoolsetc.com/index.cg...m_id=SU-137A/5 The tip says they're Shimano-compatible.

Another option:

1. Freewheel stop to outside of drive side locknut = 36.00mm
2. Center of drive side flange to outside of drive side locknut => 43.00mm
3. Fill out non-drive side IF physically possible to 120mm.
4. Re-dish wheel - the asymmetrical offsets MAY flip-flop.

Not ideal, dunno how long the drive side spokes will last IF they become the loose side after dishing. Don't know what the chainline would look like either keeping the rear at 120mm.

But at least you'd be able to install a 6 speed regular index freewheel - or a narrow 7-speed index freewheel.

=8-)

=8-)

Its a steel frame no? Just stretch it a little to fit a 6/7 speed hub and get any # of indexed shimano levers.

Internal gear hub.. Even 3 speeds are 'indexed'..

Why not? It's quite doable...

Or how about this - I reckon you could rock Ergopower without re-spacing...

If you're prepared to rebuild the hub into on OCR, you could have a 7spd freewheel at say, 123mm OLD with maybe even a bit less dish than a normal 7spd freewheel. The 5.0mm spacing of Shimano 7spd = Campy 8spd spacing.

Jamming a 123mm hub into a 120mm frame shouldn't be too much hassle.

I would say a 5 speed thumb shifter matched to a Shimano/Sunrace/Falcon 5 speed freewheel with any Shimano index RD, from the low end SIS units on up. That was a very common combination on low end department store bikes of years past.