Airburst

Normal procedure for a 3-speed hub with a cassette on it would be to use the shifter designed for the IGH in question for the hub and whatever derailleur/shifter/cassette combo you can find that works.

However, it may be that the SRAM DualDrive system uses a hub specifically designed to work with a triple left-hand shifter, although if I were in charge it I'd still design it to work with a Shimano triple shifter rather than an Ergo, as the Ergo shifter still allows the possibility of getting stuck between gears. Try looking up the spec for the DualDrive hub online.


I apologise if I'm making things any more complicated.

pstock

In fact this turns out to be a Spectro 3x7 hub.
Now, how is one supposed to use this with drop bars given the dire warnings above? or is one supposed to at all?

Peter

pstock

hmm, well now I've got STI on the left (which I think works better with the IGH) and ERgo 9S on the right (because it seems to be closest matched to the Shimano 7S cassette.
what a mishmash.
I hope it doesn't drive my wife crazy and cause her to go off this idea completely.
(but then the STI is working opposite to normal anyway- big lever takes it lower, smaller lever takes it higher.)

Airburst

It depends, if a suitable shifter isn't available for drop bars (i.e. in 23.8mm clamp diameter) there are a number of potential workarounds to get a shifter with a 22.2mm clamp (for upright bars) fitted somewhere. However, I suspect if this one's being sold by a fairly big-name (at least in the folding bike market) manufacturer with the STI shifter operating it, it'll work fine with that shifter.

Most front derailleurs go to higher gears when you pull the cable, whereas this hub clearly goes to lower ones. Therefore the shifter functions are reversed.


I know the ergonomics different hoods on two different shifters would irritate me.

dabac

Just because it currently has a stack of 7 sprockets isn't definite proof that it started life as a 7-speed cassette.
Cassettes can be disassembled and used partially for those thus inclined.
You MAY have 7 of 8 sprockets from an 8S cassette on a 7S body.
Or 7-of-9, although I suspect that would require a sizeable spacer to mount up tight and nice.

A 10S Campy shifter + most Shimano derailers will index just fine on a 8S Shimano cassette.
And it should be possible to fit a 7-of-8 from an 8S cassette on a 7S hub body.

Keep in mind that a functioning indexed drivetrain relies on a 3-way fit. Shifter pull, derailer throw, and cassette spacing. Number of speeds is a secondary concern. Mixing different numbers of speeds on shifter and cassette is functionally a non-issue. It might not be technically elegant to leave either shifter positions or sprockets unused, but it doesn't interfere with the use of the available positions.

Yeah, 31 mm or therabouts is the 7S body length.

I've seen one. but don't remember where. It seemed a bit difficult to get it right. The method was to remove the innermost sprocket, put it in a press and dish it. Then remove the spacer between biggest and 2nd biggest and reassemble. If you got the dish right, the spacing remained the same, the biggest sprocket overhung the hub body, the rd got a bit closer to the spokes but everything had a chance of working as intended.
If it was me, I'd create the overhang by cutting the center out of the biggest sprocket and welding or riveting the biggest sprocket to the 2nd biggest instead.

dabac

If you're constantly overshooting the shifting, a 3-speed IGH can be made to work just fine with only one position to hit. Once the cable has gone slack, going slacker won't change anything for the hub. And if you have a spring to soak up excess tension, the going tighter than actually needed won't hurt anything either. But you'd still need to hit the 2nd/mid gear pretty fine to avoid thrashing the hub.
I've seen bar-end shifters for Sturmey-Archer IGHs, one fo thos MIGHT work with a SRAM hub.

pstock

acck, you are correct of course. I always get my Highs and Lows confused. but the functionality is reversed.

and good point about the feel of having mixed STI / Ergo. That could be a problem. That's why I was driving towards an All Sti setup.

pstock

as it is, the cassette has a 5-sprocket welded block with loose 12 and 11 tooth sprockets (with built in spacers) added at the end.ht
though that 5-piece unit could still I guess have been part of an 8S cassette.
I see that the spacing of a 7S vs. 8S cassette is slightly different - 1.85+3.15=5mm vs 1.8+3.0=4.8mm. If I trusted my calipers, I would / could measure it.
b
but I think in the end I am just messing with the OEM setup Sachs 3x7 with Daytona brifters.
I'll talk to Bike Friday to see why they set it up like this. and why they must not have felt that a brifter with an IGH was a risk.