Whisperings of something big from the SRAM empire have been around for some months now, although until quite recently information has been sketchy. Some things were known, though – it was to be a Truvativ product, and it had a name, HammerSchmidt. The hype was that it was a revolutionary new front shifting system, and speculation soon turned to the idea that it might be a single-ring front transmission using an internal planetary gearbox.

Well, for once, the speculation turned out to be entirely correct. Although originally slated for launch at the Eurobike trade show, HammerSchmidt has managed to find its way on to so many 2009 bikes that it didn’t really make sense to keep schtum (not, as far as we know, a Truvativ product, although it sounds like it ought to be) any longer.

So, Truvativ’s HammerSchmidt ditches multiple front chainrings and a front mech in favour of one chainring and a planetary gear system transferring drive from crank to chainring. The claimed benefits are many and varied – stacks of ground clearance (the single ring is either 22 or 24 teeth and the overall diameter of the system barely bigger than that), smooth shifting whether pedalling or not, better chain management (it’s effectively got a built-in chain device) and easy maintenance. Truvativ will be offering AM and FR versions, with the AM one being a bit lighter and the FR one being a bit heavier.

This isn’t a completely new idea. Swiss company Schlumpf has been selling its Mountain-Drive (which gears down) and Speed-Drive (which gears up) chainsets for several years now. As an aside, Schlumpf also makes two-speed unicycle hubs, which is a niche market if ever we saw one… Although HammerSchmidt works on the same planetary-gear principle, it differs in a few variously-important areas. First, it should be easier to fit. One of the key elements of a planetary gear is that part of it needs to be fixed to the frame. The Schlumpf system relies on a chamfer cut into the BB shell and a conical wedge, while Truvativ has gone for the increasingly-common ISCG mount. Just having as ISCG doesn’t guarantee that you’ll be able to fit HammerSchmidt, though – the tabs have to be in a specific orientation. With considerable OE spec for 2009, though, we suspect that the majority of ISCG-equipped frames coming on to the market will be HammerSchmidt-ready.

HammerSchmidt also gives you a shifter, rather than Schlumpf’s axle-end button that you press with your heel. The shifter is styled to match SRAM’s X.0 and X.9 triggers but has a substantially different mechanism inside to deal with the fact that HammerSchmidt needs the shifter to pull cable to get a lower gear, the opposite of a derailleur. Most importantly, HammerSchmidt is designed for mountain bikes, with all of the crankset stuff we’ve come to expect – outboard bearings, oversized splined crank (a new interface, but based on Truvativ’s Howitzer setup).

So how does it work? The shift lever locks and unlocks the “sun” gear inside the planetary gearbox. With it locked, the whole assembly spins as one, so the chainring rotates once for every crank revolution just like regular cranks. With it unlocked, you get an “overdrive” gear with the chainring rotating 1.6 times for every crank revolution. HammerSchmidt will come with 22 or 24t chainrings, making the overdrive the equivalent of either 36 or 38t.

This opens up a lot of possibilities. Most bike manufacturers using the system are speccing it on big AM or FR bikes with nine-speed derailleur setups at the back, so you get something rather like a twin-and-bash setup except without a front mech, with extra ground clearance and the ability to shift at the front without pedalling. You don’t have to stick to that, though. We’re quite taken by the idea of a two-speed, with a single sprocket at the back and two at the front but with no change in chain length and associated chain-tension issues. Or how about a HammerSchmidt at the front and a Shimano Alfine at the back for a high-ground clearance, any-gear-at-a-standstill, all-tucked away Rohloff-beating 16spd drivetrain?

There’s clearly a lot to like about this idea, but we can see a few potential stumbling blocks. For a start, you’re always running on one chainring and it’s a tiddler, which is likely to wear out fast simply because there are fewer teeth over which to spread the load. On a HammerSchmidt/derailleur setup, in top gear your chain is going to be on a 22 ring and an 11 sprocket, which is going to be amazingly close to the chainstay and, we can’t help thinking, likely to rattle and clatter quite a lot. We suspect that finding a chain length that the derailleur can cope with at both ends of an 11-34 cassette could be a challenge too, but we’ll reserve judgement on that until we get to try it.

All in all, though, we suspect that HammerSchmidt will be a big hit. It’s certainly got the manufacturers excited – we’ve seen shots of bikes from Scott, Norco and Marin with HammerSchmidt and there will undoubtedly be more. We’ll give you the full low-down as soon as we get our hands on a set, but for now have a look at www.magicmechanics.com for more.