Zeroed G-1 – a radical shift in mountain bike engineering
By Ben Coxworth
May 6, 2011
It wasn't all that long ago that things like air-sprung shocks and hydraulic disc brakes were just being introduced on mountain bikes. Since then, we've heard about electronic and hydraulic shifting, microprocessor-controlled shock forks, and continuously-variable sealed gearing systems. What's next? Well, how about a bike with two chains and no derailleurs that is claimed to be better than a traditional MTB in four key areas? According to its New Zealand designers, that's what the Zerode G-1 is.
The first and freakiest thing one notices about the dual-suspension downhill bike is its drivetrain. Instead of the usual single chain reaching from the chainrings directly back to the cassette, it has two – one goes from the single chainring up to a midships-mounted Shimano Alfine internal geared hub, then another goes from that back to the rear hub. On a normal internally-geared bike, the Alfine would be the rear hub.
So why choose this set-up?
First of all, there are several good reasons to be using a mechanism like the Alfine, regardless of its location. For starters, it's much less fragile than a rear derailleur, and is relatively unaffected by mud and gravel. It can also shift easily under full chain load, or even when the bike is stopped. Additionally, chains will last longer, as they don't have to slide up and down a series of sprockets.
There are also a few reasons why internal geared hubs aren't more commonly used on mountain bikes, one of them being that the axles of such hubs typically aren't as strong as those of conventional hubs – but when not mounted on the wheel as is the case with the Zerode G-1, high axle strength isn't crucial. They can also be a little heavier, but more on that later.
By locating the gearbox in the frame's main triangle, Zerode has taken the weight of the shifting system and moved it from the back of the bike to the middle. Centralizing the weight like this is said to improve handling, and is something that motorcycle and automobile designers likewise try to do.
The G-1's unusual layout is also designed to deliver better rear suspension performance, as the weight of the gearing system has been moved from the unsprung rear swingarm to the frame – in other words, the part of the bike that moves up and down when going over rough terrain is lighter.
This isn't the first time that such a strategy has been employed on a bicycle. A similar setup was used on the GT iT1, for example, which incorporated a mid-mounted Shimano Nexus internal geared hub.
A common problem on suspension mountain bikes is a phenomenon known as "pedal bob," in which some of the energy that the rider delivers to the crankset is wasted by causing the suspension to bob up and down. This can be remedied by manually locking out the suspension, although this leaves riders constantly having to choose between pedaling efficiency and shock absorption. Since they didn't have to design the G-1 around a single continuous chainline, the folks at Zerode were able to give it an unusually-high rear pivot point, which they claim eliminates pedal bob while leaving the suspension active.
"By applying MTB variables to motorcycle theory, I could find a pivot point that would result in a chassis that you can pedal without bob," the company's Rob Metz told us. "In a nutshell, using a high pivot allows the compressive effect of weight transfer to be balanced by other effects/forces within the suspension. With a 'normal' derailleur system you are a lot more restricted in available pivot positions, and bob is minimized by using chain force to restrict suspension movement under pedaling, or shocks which do a similar thing. Generally these methods of reducing bob hinder suspension performance. With the high pivot you can achieve this elegant balance of effects/forces and get a bonus of a rearward axle path which significantly improves bump absorption on large bumps."
The G-1 is currently the only bike Zerode makes, with the first production frames having been completed just this February. Metz said that the gearbox does add some weight, but that he's convinced the gains in performance offset it. Although precise figures on complete bike and/or frame weight aren't available, he did tell us that through the selection of lightweight components, some riders have gotten their G-1s down to about 16.5 kg (36.5 lbs). He added that a less hefty trail bike is presently in the prototype stage.
Prospective early-adopters can buy a G-1 frameset – including gearbox, shifter, shock, chain tensioner and sprockets – via the Zerode website, for about US$3,600.Share
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