Sixty Fiver

A few years ago I set up a dual drive on a Sturmey Archer 3 speed to expand the drive's range and reduce those 33% jumps between gears and did that on a Raleigh 20 folding bike which required a lot of fabrication work since the bike was not designed to use a derailleur.

It did give me a stump pulling low gear and a pretty nice top gear for what was a very utilitarian bike.

This evening I did another dual drive conversion on my Kuwahara Shasta which was already set up as a 3 speed and since it was designed to run a derailleur the conversion was actually quite simple so I thought I would share this.

This can be done to any 3, 5, or 8 speed and if you don't mind the look of a derailleur it does offer the best of both worlds...

The first thing you need to do is remove the 1/8 SA cog and the two spacers and replace those with 2 Shimano dished cogs which are 3/32 and they fill that space nicely. I went with a 2 cog difference which gives me a 12.5% jump when I shift the derailleur which is essentially a high low range.

With a 3 cog difference the jump will be 16.7%, with 4 teeth 22.2%.





The KMC 1/8 chain was replaced by a KMC 7 speed chain.

The Shimano 600 road derailleur works beautifully and when you set it up you need to lock the derailleur high and low limits so that it only shifts across the 2 cogs, and an overshift down will send the chain toward the spokes so you want to make sure this is dead on.

The shifting is being handled by a Suntour half ratchet thumb shifter which has a nice light action and plays well with the 600 derailleur and I positioned it so that I could reach it with my thumb.


High gear.


Low gear.

Running a 42:20 my previous range was 39/52/69 which was good for winter riding but with nice weather the 52 was too low and that's a big jump to the 69 and like they say, you are often in between gears with a 3 speed.

The new range with the 40 and a 16/18 is 43/48/57/65/76/86 and on the test ride the middle position (direct drive) gives me that 57/65 gearing which is just about right for stop and go city riding and the 76 is spinnable on the straightaways... I will save the 86 for screaming downhill runs and tail winds.

I gave up a little bottom end but with some new slicker / faster tyres I won't miss it and 43 gear inches is low enough that I can still spin up a 12% grade with one good leg.

I don't think the final look is all that unattractive.





Rode 20 km with this tonight and found that the expanded range was very nice and found myself shifting between the high low in the second position the most and like any IGH I could pull up, stop, and downshift the three speed to 1st to have a lower gear for take off.

It really improved my riding speed as it has 6 nicely spaced gearings with no overlap which allowed me to pick the best gearing for what was a most windy night and the high / low with the 1st gear was very nice on some longer steeper climbs.

Hope you enjoyed the tutorial.

SF

Sixty Fiver

This idea is an old one although when I did the first and second conversion (this is the third) I was not aware that once upon a time you could have bought a kit to add a double or triple cog set to a Sturmey Archer drive.

They were sold by Cyclo Benelux and the 3 speed kit required that you use a longer SA axle and/ or spacers while this modern 2 speed conversion can be done without any axle changes or spacers since it utilizes narrower cogs and you retain a nice chain line.

tcs

Is there something special about the Shimano cogs, or would SRAM or Sturmey 3/32 dished cogs work as well?

fietsbob

I had a Cyclo, (UK? made), steel piece machined with 3 sprockets in it.
was the early 60's then.. fit right on my J,C,Higgins [Puch?] 3 speed,
put on a cottered Williams triple crank too, also without changing the spindle..
I think ... it was like 50 years ago, after all .

for tcs .
there was a de-facto standard cog spline for 3 speeds,
that was sturmey archers Aw3's.
but SA made 1/8' thick ones , except like for Brompton. they are small.. 13. 14t

new parts Sachs [now sram] made a 2 cog driver for Mk 3 brompton,
3/32" .. 13/15 using Aw 3 Spline
current Mk4 Sturmey for Brompton BWR
uses a shimano bmx spline, at present..

Sixty Fiver

Any 3/32 dished cog with the right spline pattern will work... I am just used to having tons of extra Shimano ones kicking around so use those and they are quite common and inexpensive.

cycle_maven

I did the same thing by grinding the splines on a couple of 7-speed hyperglide sprockets (took apart a cassette) to the approximate shape of the three half-round tabs of the Sturmey-Archer sprockets. With a 7-speed spacer, the stack exactly fits on the Sturmey-Archer hub.

silver_ghost

Wow. Awesome idea Sixty, thanks for sharing.

When I ran a 1x8 setup, I couldn't keep the chain from hopping off the chainring once in a while without putting a dummy front derailluer on. Have you ever had this problem? I suspect the "jerkiness" of indexed shifting contributed to my issue.

fietsbob

I think Sturmey Archer now has a competitor to the SRAM 9x3,
they already have taken over supplying the BWR designed for Brompton,
a 2x3, Sram was the last contracted source of the similar thing ..
SA uses shimano spline , the SRAM adopted the AW3 spline,
2 cogs held in with a snap-ring.

Sixty Fiver

With only two cogs that are pretty much in line with the chain ring and some higher chain tension I could not get the drive to misbehave at speed or under load... the 600 derailleur was used but is in fine shape and shifts very crisply.

tcs

Indeed. My copy of Reginal Shaw's Cycling (1950) suggests half steps of 19 and 22 tooth cogs with a 46 tooth chainwheel for sporting use or 18 and 21 tooth cogs with a 36 tooth chainwheel for touring, when combined with the AW hub.

Sturmey 7-speed IGHs perhaps, but not the 8.

tcs

It might have contributed, but rear-derailleur-only drivetrains propensity for tossing their chains has been a documented problem since at least the late 1920s.

fietsbob

the 8 uses a bigger hole in the sprocket, I note only 19?, 23 & 25 t sprockets listed.
[+ the all but 1st overdrive gears make it a folding bike hub,
little wheels small chainring.

Dan Burkhart 

This is the conventional wisdom to which I also subscribed until recently. My successful conversion of a 700c wheeled bike to an SA 8 speed says otherwise. Time will tell if it works out long term. Stay tuned.

tcs

The bike pictured has a range of 31-100 gear inches.

tcs

Well, yes, but actually the real reason is the S-A 8 driver only has room for a single cog, like Shimano and SRAM IGHs and unlike the traditional S-A 3-4-5-7 speed drivers that have room for a cog and two spacers (or as Sixty Fiver has reminded the neophytes, two back-to-back cogs).