Sturmey Archer Dual Drive

For discussions about bikes and equipment.
Stradageek
Posts: 567
Joined: 17 Jan 2011, 1:07pm

Sturmey Archer Dual Drive

Postby Stradageek » 10 Aug 2019, 8:05am

This is probably a question for Brucey (again!).

I have an SRAM 3x7 dual drive on my BikeE which works beautifully and I'd like to build a similar system as a little bike project.

I have an old Hercules 3-speed hub with a screw-on sprocket. The screw thread accepts a 5/6/7 speed block but this is of little use because the axle is then too short to mount the wheel.

Are long SA axles obtainable and or would they be so long as to be vulnerable to bending? Or could I take an angle grinder to a 5/6/7 speed block and make a 3x2 or 3x3 system to reduce the required axle length?

I suspect someone (probably Brucey) has tried this; can anyone advise if this winter retirement project is doomed to failure?

Cheers

Stradageek

Brucey
Posts: 34785
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer Dual Drive

Postby Brucey » 10 Aug 2019, 8:47am

you can buy longer axles that fit the older SA (Hercules is rebadged SA) hubs. Currently they are made differently from older axles so they ought to be stronger. Older axles had the sun pinion riveted to it; newer ones are 'all solid'. All SA 3s hubs made in Taiwan use this style of axle and I have yet to see one break in the middle like they used to. The newer NIG axles won't fit older hubs but SA make 'all solid' axles that fit older hubs too.

[The newer axles are not perfect though; I have seen a few that were not made properly and this manifested itself by crumbling threads on the end of the axle.]

If you just want two sprockets the easiest way to do it is to use a splined driver. The splines on Non-NIG drivers are long enough to accommodate two sprockets without modification. No other changes to the hub are required. All this is required is a splined AW driver (from ~1950 to 2000).

It is also possible to build threaded sprocket clusters that make the most efficient use of the space available and therefore work with shorter axles; there is lots of space to the left of the standard sprocket position, which is not exploited if a standard threaded freewheel is mounted to the hub.


If you want to buy something off the shelf then CS-RF3 hub will allow 3x8 to 3x10 gearing, but it is quite a bit wider than your current hub.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Stradageek
Posts: 567
Joined: 17 Jan 2011, 1:07pm

Re: Sturmey Archer Dual Drive

Postby Stradageek » 10 Aug 2019, 10:56am

Thanks Brucey, I think I understand all that.

Long axles would also allow me to fit a standard AW3 hub to an aluminium frame that can't be cold formed to the smaller OLD (I like converting old MTBs into nice town bikes) - any idea where I can buy them?

Thanks again

Stradageek

Brucey
Posts: 34785
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer Dual Drive

Postby Brucey » 10 Aug 2019, 11:11am

HSA370 is 163mm long, fits pre NIG AW hubs and is available from SJS. With careful selection of nuts, washers and dropout thickness, this can be made to work up to about 130mm oln, perhaps a touch more. However IIRC much of the extra length is on the left side not the right.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~