We recently brought you news of Truvativ's new HammerSchmidt front shifting system, that dispenses with multiple chainrings and a derailleur in favour of one chainring and some planetary gears inside a stout casing that doubles as a bashguard. HammerSchmidt offers two gears. With the three chunky pawls inside engaged with the 24-tooth ratchet, the chainring spins at the same speed as the cranks and thus behaves as the 22 or 24T chainring that it is. Release the pawls, the planetary gears come into play and the chainring rotates 1.6 times for every crank revolution, giving the equivalent of a 36 or 38T ring.
Interbike's Outdoor Demo gave us a chance to take HammerShmidt for a ride in the company of Truvativ parent company SRAM's Greg Herbold and Tyler Morland, both of whom are alarmingly quick - two fast loops of the demo trails in the desert heat just about finished me off...
Riding HammerSchmidt takes a bit of getting used to. For a start, the shifter works back to front. Pulling cable disengages the pawls, so pressing the main lever puts you in the low 1:1 gear. Hit the release lever and the pawls pop out, instantly getting you into overdrive. Front derailleurs will typically only happily shift at a couple of points in a crank rotation, but HammerSchmidt will shift at any point while pedalling, or while coasting, or while pedalling backwards (should you so wish). The throw on the shifter lever is a tiny bit longer than a regular derailleur system, too - if you don't push it quite to the click then the pawls don't disengage.
The other thing that takes a while to get your head around is using the full range of the rear cassette in what feels like the granny ring. Ordinarily it's good practice to stick to the three or four biggest sprockets in the granny, but because HammerSchmidt's single chainring is in the middle ring position the whole cassette becomes fair game and 24/11 becomes a perfectly legitimate gear. This is rather important given the substantial difference between the two front ratios - you need access to those smaller sprockets to bridge the gap.
It definitely requires a bit of relearning about how best to use the gears at your disposal, but you quickly start to take advantage of the instant shift. Rather than shifting well ahead of time you can wait until you absolutely must shift, safe in the knowledge that you'll get the gear. The Bootleg Canyon test loop included a substantial dip, with a rocky drop into one side and a loose scramble up out of the other. With a derailleur setup you need to pick a gear that's a good balance between gaining speed on the downslope and getting up the other side - there's not really a chance to shift once you're in the section. With HammerSchmidt you can barrel in using the overdrive gear, crank it as far as you can up the other side and if you're not going to make it, tap the shifter and immediately drop to 1:1.
Questions will inevitably be asked about efficiency. There's a quiet whirring noise from the cranks in the overdrive mode, which means that some of your effort is going somewhere other than the back wheel. Truvativ isn't yet quoting official figures, but unofficially it's single-digit percentage losses. That doesn't seem too bad given that the overdrive mode will be mostly used going down hill. Besides, the whirring is about the only way you can tell what gear you're in...
So what of the other potential issues that we pontificated upon before setting eyes on, and having a go with, the real thing? With just one 22 or 24T chainring, we'd expect it to wear out pretty quick. But Truvativ has very sensibly used a sturdy steel chainring that's both cheap and easy to replace - it fits on to splines inside the casing and is held in place by a simple C-clip. Also working on the ring's favour is that the chain's not moving on and off it frequently.
We also expected the system to be a bit clattery on account of the top run of chain being generally very close to the chainstay, particularly in the 11T sprocket at the back. But there was not a hint of clatter. This is down to two reasons. First, there's not much chain - the demo bikes had short-cage X.0 mechs and 14 fewer chain links than a normal twin-and-bash setup. Second, a side-effect of HammerSchmidt's design is that the chainring can freewheel. A lot of clattering on conventional bikes is due to the top run of chain going slack when coasting. Some suspension bikes can develop a substantial sag in the chain under compression, and the general flapping about of the rear derailleur can contribute too. But because HammerSchmidt's chainring can rotate forwards while the cranks are still, any excess chain in the top run tends to just drift out.
From an initially mildly sceptical viewpoint, we came away from riding HammerSchmidt thinking very highly of it. There are a lot of advantages to the system (on the right kind of bike - XC racers need not apply) and not many disadvantages. Even simple things like being able to come to a stop in a high gear and easily shift to a lower one before setting off again quickly become second nature. Only time will tell how well it holds up under members of the public (who often seem to be able to break things that professional riders don't), but first impressions are very good indeed.
