The SRAM Automatix two-speed hub (production discontinued in 2017) has received good reports for reliability. While Sturmey-Archer two-speeds are shifted by backpedaling, the Automatix uses centrifugal force to shift it at a particular speed -- and so, the hub doesn't annoyingly shift every time the coaster brake is used.
The gear ratios are 1.00 and 1.36 (64/47), as with the old Sachs Automatic and Duomatic hubs.
SRAM reports that several versions were available, with coaster brake, or to fit a disc brake rotor or Shimano Rollerbrake, also with an aluminum shell -- see SRAM page.
Weights -- also see the SRAM page -- thanks to Ulrik Dobashi Hansen::
940 gram - Alu version for disc brake (32H)
1210 gram - Steel version without coaster brake
1384 gram - Steel version with coaster brake
(All weighed with axle nuts, spacers/washers and dust cap, but without sprockets and brake rotor)
The main difference in weight between especially the steel and aluminum versions, comes from the massive wall thickness of the steel of the left inner profile of the mandrel-forged hub shell. The somewhat similar and contemporary SRAM i-Motion 3 hub shell had a more tapered shape and lathe lightening cut in that area.
The sprockets are the standard three-lug ones as used with most internal-gear hubs, but a Gates belt-drive option was available.
The Automatix is relatively simple and easy to service, though as usual with SRAM geared hubs, parts availability in the USA is an issue, even more now that the hub is no longer made. Look to eBay. User Instructions are available online. Ulrik Dobashi Hansen has further information including parts substitutions and disassembly photos on his Web site.
Aaron Goss of Aaron's Bicycle Repair, Seattle, Washington, USA, rebuilds these hubs and has been kind enough to provide the helpful photo and diagram below.
The speed at which the hub shifts may need adjusting. That is relatively easy to do, though it requires disassembly of the hub -- also see below.
The SRAM Automatix coaster-brake hub, disassembled.
There is only a single spring, despite the two centrifugal flyweights,
center of picture. Yes, that is correct!
Aaron reports that the hub shifts at too low a speed (and so,too low cadence), but it can be adjusted:
Also, there is info online on how to change the shift point to a higher speed because it shifts way too soon! I have done it and it works great! http://mccraw.co.uk/sram-automatix-review/ (now in the Internet Archive; update with better photos)
That article includes lots of additional helpful information about the hub.
The Automatix is available with 28 or 36 spoke holes. The shift point with 36 holes is around 135 RPM, or 10 mph (16 km/hr) on a bicycle with a 26" wheel. Apparently, the version with 28 spoke holes is intended for smaller wheels and shifts at higher RPMs. This version is reportedly rare, and 28 spokes aren't a good idea on a utility bike with large wheels. Another way to raise the shift point would be to install the internal mechanism from a 28-hole hub into a 36-hole shell, but with small wheels an adjustment would be needed even with the 28-hole version. Perhaps installing a spring behind the second flyweight would also raise the shift point -- though you would then have to acquire a second spring.
Removing one of the flyweights might work poorly: gravity would have an uneven effect as the wheel rotates. An alternative method that has proven to work is to grind won both weights to lighten them. There is an example photo on a page on Jens Hansen's site.
The instance shown is an extreme case of a 36-spoke Automatix in a 20 inch wheel, requiring a very big change in the shifting point. Less would need to be removed for the more usual change from 16-18km/h (10-11 mph) to ~20km/h (12 mph) in a 26-28 inch (ETRTO 559mm-622mm) wheel.
Where you want to set the shift point depends on your personal preference and the drive ratio. Typically,the top gear will be 75-80 gear inches (6 to 6.5 meters development) for level-ground riding, and the lower gear should engage when the pedaling cadence gets below 60 rpm. The lower gear will then provide a boost for starting and moderate climbs. You will coast downhill. This hub is convenient for relatively flat urban riding, but with only two drive ratios, it can be frustrating for steeper climbs. Check our Gear Calculator to figure out what sprocket and chainwheel will work for you.
Freewheeling versions of the hub may be used with a chain tensioner and front derailer to give you four or six speeds. This option is available thanks to the speed-dependent shifting -- it won't work with a kickback hub, because tensioning the lower run of chain is necessary to make the hub shift. You'll probably want the ratio between sizes of double chainwheels to be half that of the hub, to give you finer steps in speeds. When the hub shifts up, you shift the derailer down, and vice versa. With three chainrings, the small inner one can provide a "bail-out" gear. A small wheel reduces the stress on the hub, but on the other hand, this hub is not suited for a tandem or cargo bike.
Last Updated: by John Allen
