Advice on SRAM dualdrive/1:1 mechs

I'm charged with the maintenance of a Brox Compact that uses a SRAM
3x9 DualDrive. Basically it's a three-speed hub with a 9 speed
cassette stuck on the side, and a shifter that has a twist grip and a
thumbshift integrated in the same unit: thus, can shift both gears
with only one hand.

However, the hub is not part of a wheel. The Brox has two chains: one
running from the front of the boom where the chainring is, to the
middle under the seat, and the second running back to the rear axle.
The hub is under the seat too: it's driven by the front wheel and it
has a sprocket bolted to its side that drives the rear wheel. What's
the problem here? Ground clearance. It's very easy to ground the
jockey cage against speedhumps, kerbs etc. This has bent the
derailleur, and can't be doing the chain much good either.

The picture at http://www.lfns.co.uk/images/bike/thamesfestival.jpg
shows more or less how it's put together, if you can distinugish the
metal bits from the shadows.

So you're going to say "shorter derailleur" ... but wait, there's
more. We need a shifter for the hub. If we continue with the
integrated shifter (and it _is_ nice being able to do the whole thing
with one hand), we're stuck with the SRAM 1:1 cable pull ratio, and
they don't seem to make many mechs for that with a short cage. What
you see is a "long" X7, I also have looked at a "medium" X9, but it's
only about 10mm shorter. The only one they describe as having a
"short" variant is the X0, which is kinda pricey, and not having
actually seen it I don't know if it's _really_ short or if it's just
another half inch, The cassette ratio is fairly close, and we only use
one chainring, so there's no real need for a long cage.

So I'm thinking (always dangerous)

* is there a thumbshifter suitable for the hub that we could squeeze
onto the same handlebar as a separate 1:2 twist grip unit in a
reasonable ergonomic arrangement? Then we'd have a wider choice of
mechs. I don't know if the hub cable pull is the same for other SRAM
hubs or for others from other manufacturers

* or maybe we'll stick with the SRAM stable, and invest in disposable
gear hangers so that next time the cheap bit breaks before the
expensive bit bends. But unless the rider has necessary mechanical
aptitude to replace the hanger (on the road, in the dark) it lacks
somewhat as a "get you home" option, and even then it's not really
desirable.

* other ideas? Most of the time we're riding it we find that the hub
gear is far more useful than the derailleur anyway just because it
shifts faster: we use the hub for starting up and most low/medium
speed rinding, and the derailleur for fine-tuning on fast bits. Don't
think we can afford a Rohloff, but maybe a Nexus or similar? It is
nice to have a range of close ratios at around the 15km/h-20km/h
speed, though, otherwise it's hard work keeping up with the skaters.

Budget rather depends on whether we're talking about one-off costs or
disposable items: if it takes £100 or so to fix it properly that's
fine, but I don't want to be paying £60/pop for items that will get
bent on traffic calming features every couple of months.

What does the panel think?


-dan

--
http://www.coruskate.net/

On Tue, 02 Jan 2007 13:45:47 +0000, Daniel Barlow
wrote:


I'm charged with the maintenance of a Brox Compact that uses a SRAM
3x9 DualDrive. Basically it's a three-speed hub with a 9 speed
cassette stuck on the side, and a shifter that has a twist grip and a
thumbshift integrated in the same unit: thus, can shift both gears
with only one hand.

However, the hub is not part of a wheel. The Brox has two chains: one
running from the front of the boom where the chainring is, to the
middle under the seat, and the second running back to the rear axle.
The hub is under the seat too: it's driven by the front wheel and it
has a sprocket bolted to its side that drives the rear wheel. What's
the problem here? Ground clearance. It's very easy to ground the
jockey cage against speedhumps, kerbs etc. This has bent the
derailleur, and can't be doing the chain much good either.


Doesn't strike me as the best of designs. The brox that is, not the
dualdrive. Anyhow, you're stuck with it.


snip

* is there a thumbshifter suitable for the hub that we could squeeze
onto the same handlebar as a separate 1:2 twist grip unit in a
reasonable ergonomic arrangement? Then we'd have a wider choice of
mechs. I don't know if the hub cable pull is the same for other SRAM
hubs or for others from other manufacturers

What about the other way - put a bar end/down tube lever to shift the
mech and keep the existing twist grip for the hub? My Sachs/Sram 3 x 7
was made before the cleverness of the dual drive, so I've always
operated it from two twist grips - one for the hub and one for the
mech. I *think* the mech has a 1:2 pull though.



Tim

Daniel Barlow twisted the electrons to say:
* is there a thumbshifter suitable for the hub that we could squeeze
onto the same handlebar as a separate 1:2 twist grip unit in a
reasonable ergonomic arrangement? Then we'd have a wider choice of
mechs. I don't know if the hub cable pull is the same for other SRAM
hubs or for others from other manufacturers

Well if you're prepared to sacrifice the "all on one hand" aspect, then
there are DualDrive controls that are available as two seperate grip
shifters (my Grasshopper is so equipped). Getting ahold of one of them,
would enable you to change the derailleur and it's shifter to whatever
you desired ... In fact, come to think of it, if you got some kind of
thumb-shifter for the derailleur then you could maybe keep the "one
handed" aspect?

* other ideas?

Could you modify the Broxx so as to raise that section of the chainline?
(Have to confess I've never given a close look to the Broxxi(sp?) that
I've seen.) That could, if it's even possible, go right out the far side
of your budget faster than the Rohloff option but it's the only other
possibility I can think of ATM.
--
These opinions might not even be mine ...
Let alone connected with my employer ...

In article
Daniel Barlow wrote:
snip
So you're going to say "shorter derailleur" ... but wait, there's
more. We need a shifter for the hub. If we continue with the
integrated shifter (and it _is_ nice being able to do the whole thing
with one hand), we're stuck with the SRAM 1:1 cable pull ratio, and
they don't seem to make many mechs for that with a short cage. What
you see is a "long" X7, I also have looked at a "medium" X9, but it's
only about 10mm shorter. The only one they describe as having a
"short" variant is the X0, which is kinda pricey, and not having
actually seen it I don't know if it's _really_ short or if it's just
another half inch, The cassette ratio is fairly close, and we only use
one chainring, so there's no real need for a long cage.

So I'm thinking (always dangerous)

Me too. :-) Why not just cut down the cage of the existing derailleur?
Slice an inch out of the middle, and braze or hard solder the offcuts
back on to hold it together.

Tim Hall writes:

On Tue, 02 Jan 2007 13:45:47 +0000, Daniel Barlow
wrote:


I'm charged with the maintenance of a Brox Compact that uses a SRAM
3x9 DualDrive. Basically it's a three-speed hub with a 9 speed
cassette stuck on the side, and a shifter that has a twist grip and a
thumbshift integrated in the same unit: thus, can shift both gears
with only one hand.

* is there a thumbshifter suitable for the hub that we could squeeze
onto the same handlebar as a separate 1:2 twist grip unit in a
reasonable ergonomic arrangement? Then we'd have a wider choice of
mechs. I don't know if the hub cable pull is the same for other SRAM
hubs or for others from other manufacturers

What about the other way - put a bar end/down tube lever to shift the
mech and keep the existing twist grip for the hub? My Sachs/Sram 3 x 7
was made before the cleverness of the dual drive, so I've always
operated it from two twist grips - one for the hub and one for the
mech. I *think* the mech has a 1:2 pull though.

The dualdrive on my 'bent works with two bar end shifters. The one for the
hub has been modified so that it has one click for the middle gear, the
other two gears are 'far in' or 'far out'. The middle one needs to be
tuned right, that's what the yellow indicator on that box thingy is for.

Roos

in message , Daniel Barlow
') wrote:


I'm charged with the maintenance of a Brox Compact that uses a SRAM
3x9 DualDrive. Basically it's a three-speed hub with a 9 speed
cassette stuck on the side, and a shifter that has a twist grip and a
thumbshift integrated in the same unit: thus, can shift both gears
with only one hand.

However, the hub is not part of a wheel. The Brox has two chains: one
running from the front of the boom where the chainring is, to the
middle under the seat, and the second running back to the rear axle.
The hub is under the seat too: it's driven by the front wheel and it
has a sprocket bolted to its side that drives the rear wheel. What's
the problem here? Ground clearance. It's very easy to ground the
jockey cage against speedhumps, kerbs etc. This has bent the
derailleur, and can't be doing the chain much good either.

The picture at http://www.lfns.co.uk/images/bike/thamesfestival.jpg
shows more or less how it's put together, if you can distinugish the
metal bits from the shadows.

So you're going to say "shorter derailleur" ... but wait, there's
more. We need a shifter for the hub. If we continue with the
integrated shifter (and it _is_ nice being able to do the whole thing
with one hand), we're stuck with the SRAM 1:1 cable pull ratio, and
they don't seem to make many mechs for that with a short cage. What
you see is a "long" X7, I also have looked at a "medium" X9, but it's
only about 10mm shorter. The only one they describe as having a
"short" variant is the X0, which is kinda pricey, and not having
actually seen it I don't know if it's _really_ short or if it's just
another half inch, The cassette ratio is fairly close, and we only use
one chainring, so there's no real need for a long cage.

I think - but I'm not certain - that the new SRAM road mechs have the same
pull ratio. If not, the X0 certainly does come in short cage - the one on
Steve Pete's downhill bike looks just like a time trial derailleur; his
cassette is very close ratio, about 12-21. But as you say, expensive.

It might be worth seeing of the cage plates of the short-cage X0 are
available as spares, since they'd fit on an X7. I run an X9 with X0 cage
plates and jockey wheels cadged off the SRAM support mechanics at last
year's mountain bike world cup.

* other ideas?

Rohloff?

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

Anagram: I'm soon broke.

Simon Brooke wrote:
It might be worth seeing of the cage plates of the short-cage X0 are
available as spares, since they'd fit on an X7. I run an X9 with X0 cage
plates and jockey wheels cadged off the SRAM support mechanics at last
year's mountain bike world cup.


SRAM x9 now has a short cage option which might prove less expensive?
http://www.sram.com/en/srammountain/...derailleur.php

"Simon Brooke" a écrit:

I think - but I'm not certain - that the new SRAM road mechs
have the same pull ratio.

Unfortunately they don't. Cable pull per shift is advertised as 3mm, and
10spd cassette spacing is about 4mm.

James Thomson

Thanks for all the replies. Espeically to Simon, whose suggestion of
mix'n'matching parts from the X0 set me to further browsing, and
squeaker, for the headsup that the X9 has a short cage option. Either
that's new for 2007, or I overlooked it in the SRAM service manuals.

Having then noticed that the X9 super short is in stock at
ChainReaction, that they have a nice big picture of it so I can see
that it actually does exist and _is_ short (take note, other online
retailers: more product information never ever hurts), and they have a
tenner off, suddenly my credit card just creaked a little harder.

I thought (fairly) long and hard about using this as an opportunity to
get out of SRAMworld, but the more I went poking around for opinions
on them the stronger the impression I got that people seem to like
them a lot. And given that the riders of this crate aren't guaranteed
to have much mechanical sympathy, I like the idea that the 1:1 will
shift better with less fuss.

Tim Hall:
Doesn't strike me as the best of designs. The brox that is, not the
dualdrive. Anyhow, you're stuck with it.

I'm curious: best in the "something else does the same job better"
sense, or in the "redefine the job a bit" sense? It took us ages to
get hold of a Brox and I think we're pretty happy with the basic
premise. The bare frame is certainly heavy in comparison to say, an 8
Freight (which I've also ridden in a very similar role), but by the
time it's loaded up with car batteries and PA speakers it's really not
that bad. And much easier to keep vertical when moving off at traffic
lights. Can even ride it no-handed ;-)

(Fortunately, I don't think there are pictures of me riding it while
balancing on the boom. That got a whole lot more difficult since we put
toeclips on it though ;-)


-dan

--
http://www.coruskate.net/

On Wed, 03 Jan 2007 17:29:15 +0000, Daniel Barlow
wrote:



Tim Hall:
Doesn't strike me as the best of designs. The brox that is, not the
dualdrive. Anyhow, you're stuck with it.

I'm curious: best in the "something else does the same job better"
sense, or in the "redefine the job a bit" sense?


Sorry, poor use of words on my part. Certainly the Brox lookds ideal
for what you want. It's just having the rear mech _that_ close to the
ground (and the photo made it look very close) didn't seem ideal.


Tim