SRAM Automatix

SRAM Hub

SRAM is introducing a two-speed auto-shift internal gear hub to the European market this summer. It’s my understanding that the internal shifting mechanism is controlled by centrifugal force; when you reach a certain speed the hub automatically shifts to a higher gear, and when you slow down, it automatically shifts down (the shifting points can be preset at 7.5, 8.7 or 11.2 mph). Specs as follows:

  • Speeds: 2
  • Gear Ratios: 1:1 and 1:1,37 = 124%
  • Spoke Holes: 28 or 36
  • Sprockets: 15, 16, 17, 18, 19, 20, 21
  • Finish: Ni-Chrome-plated
  • Weight: 980 gr
  • Shifting points: 7.5, 8.7 or 11.2 mph
  • Brake: Coaster

Automatic shifting is nothing new. From what I can discern, this hub is based upon the rare Sachs Torpedo-Automatic. Then there was Shimano’s ill-fated 3-speed auto-shift “Coasting” drivetrain. And though it’s not exactly an automatic, Sturmey Archer seems to be doing well with their 2-speed kick-shift hub.

I’m not convinced we really need automatic shifting on bikes when we already have indexed internal gear hubs, but for those who want the simplicity and clean lines of a single speed while needing the advantages of a second gear, this is an interesting alternative.

There’s no word yet on price or whether it will be imported into the U.S. The Automatix is the first among other new IGHs from SRAM due out later this year.

View the Spec Sheet [PDF] →

[Hat tip to Jeff L. —ed.]

10 Responses to “SRAM Automatix”

  • Andy says:

    Though I find these parts a bit pointless for someone to choose to buy, I can see the simplicity being a major plus for bikeshares in the city. The new Michelin no-flat tires, auto shifting, blinking lights always on, etc. makes it so you can just jump on and go.

  • Daniel M says:

    Could you explain to me how a 1:1 bottom gear and a 1:1.37 top gear (i.e output speed = 100% of input speed to output speed = 137% of input speed) gives us a gear spread of anything other than 37%? I have a math background and can’t figure out where the 124% figure comes from.

  • Joseph E says:

    Re: “Could you explain to me how a 1:1 bottom gear and a 1:1.37 top gear (i.e output speed = 100% of input speed to output speed = 137% of input speed) gives us a gear spread of anything other than 37%?”

    Daniel, IGH are misleadingly represented as thought the gear ratio were a percentage. So the Shimano 3 speed hubs, which have about a 1.8 to 1 ratio of gears, are said to have a “180% range”. Of course, by this logic, a single-speed bike has a 100% range, which is silly.

    But I actually don’t know why they are calling it 124%. If the ratio is 1 to 1.37, it would normally be advertized as “137%”.

  • marcin says:

    The automatic hub is sort of curiosity more than anything else. What I’m really waiting for is some info on new 7 and 8 speed hubs from SRAM. Does anyone know anything?

  • Daniel M says:

    @ Joseph E:

    Thanks for the reply. On further reflection, 137% would seem to be right. Saying a single-speed has a 100% “range” is a bit counterintuitive, (“overall multiplier” would be preferable), but it makes sense because the top ratio is exacly 100% of the bottom ratio. It’s the old story of “100% more” vs. “100% of”. As long as we are being consistent in defining “range” as “% of”, there is no problem.

    Just to be sure, I looked at the other IGHs that get discussed a lot:

    If you look at Shimano’s own material for the 11-speed Alfine…

    http://www.shimano.com/publish/content/global_cycle/en/us/index/products/0/alfine/product.-code-SG-S700-S.-type-..html

    …they list the top gear ratio as 2.153 (or 2.153:1) and the bottom as 0.527 (or 0.527:1). 2.153/0.527 = 4.085, so Shimano’s claim of 409% overall range is consistent with the math.

    Rohloff…

    http://www.rohloff.de/en/products/speedhub/sprocket_ratios/index.html

    …claims a bottom ratio of 0.279 and a top ratio of 1.467; 1.467/0.279 = 5.258, so their 526% ratio is also consistent. For even more fun, taking the 13th root of this number (because there are 13 actual steps between gear 1 and gear 14) yields 1.1361, which lends credence to their claim of evenly-spaced 13.6% jumps between adjacent gears.

    Over at SRAM…

    http://www.sram.com/sram/trekking-comfort/category/261

    …they don’t give us the actual ratios of the gears themselves, but they claim that their 9-speed freewheel has an overall range of 340% and that all of the jumps between gears are between 14% and 17%, which seems reasonable because the 8th root of 3.40 is 1.1652, for an AVERAGE jump of 16.5%. They furthermore claim that the 3-speed freewheel has an overall range of 186%, but again no individual gear ratios.

    In the case of the spec sheet for the 2-speed automatic linked to in this post, it appears there must be a misprint. Assuming the bottom gear is, in fact, direct-drive, either the top gear is actually 1.24:1 or the overall range is 137%.

    Feel free to correct me if I’ve made some obvious mistake, as I did in my first post.

  • Ash L. says:

    I have a Sachs two-speed automatic hub that I bought attached to a POS Murray Monterrey. I am currently building it into a 27×1 1/4 inch road rim and will be putting it into a much faster Schwinn Le Tour. The coaster brake is about as good as coaster brakes get but I’m still planning to add a front caliper brake down the line since those hubs were mostly made for foldies and cruisers that rarely went about 11MPH.

  • Warren says:

    I hope this is the first of a new direction for IGH. If they make this work with 5-9 gears it would be great to just commute to work and not worry about gears but not ride a single speed either.
    Can’t wait to see what the price of the 2 speed will be….

  • Graham says:

    I think that I agree with Warren on this one. I do wonder how these hubs would feel on inclines and such, but I think that it is an intriquing idea.

    Why did they incorporate a coaster brake?! I would think that there is quite a niche market out there for folks who like the lines and looks of a single speed, but prefer to have their own brakes.

    At least offer a version of it without a coaster brake!

  • Thor says:

    gonna be a very cool single speed looking folding bike wheel with maybe a belt drive ….

    lets see if I can get something like that to sell down the road, with the coaster brake it would be a totally simple, clean looking bike which would perform rather nicely.
    if the cost could be kept down ..it would be a winner.

    thor

  • Ash L. says:

    I built up that wheel today with the Sachs automatic hub. I posted some photos here: http://onelessminivan.tumblr.com/post/6371252169/fun-with-wheel-building and will be installing it on a 1980s Schwinn Le Tour mixte frame this Sunday.

 
© 2011 EcoVelo™