Of all the things that cause wear, tear and noise on a mountain bike, chain slap is certainly one of the most annoying. As its name implies, it occurs when rough terrain causes the chain to be flung up and down, slapping against the chainstay as it does so. While there are things that can be done to minimize it, California-based Cycle Monkey has taken a unique approach – the company has helped to design the one-of-a-kind Battleaxe mountain bike, that features a unique chain slap-unfriendly drive train.
Chain slap can occur on any type of mountain bike, but it's particularly common on full-suspension models. Putting it simply, this is because the swingarm moves up and down relative to the rest of the frame. The cassette moves with that swingarm, taking the back end of the chain up and down with it. The front end of the chain, however, remains in place, joined to the rest of the frame by the chainring. As a result, the chain doesn't always remain parallel to the chainstay, and the two can come into contact.
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Working with Idaho's Oxide Cycles, Cycle Monkey developed a two-chain drive train that addresses the problem. One short chain runs from the frame-mounted chainring to a swingarm-mounted gear, then the other longer chain runs from that gear to the rear wheel.
"By creating two separate chain lines with a shared gear, you're able to isolate the chain that is next to your crank and your bottom bracket from the chain that is operating your rear hub," explained Cycle Monkey's Katie Brown, who was demonstrating the system at the North American Handmade Bicycle Show. "You don't have direct drive any more, you have this linkage, but by isolating the chain that runs from the hub to the front of the rear triangle, it allows the swingarm to move without changing that portion of the chain line."
Instead of a conventional rear derailleur, the Battleaxe utilizes a Rohloff Speedhub 14-speed internal-geared hub. Besides being necessary for this particular configuration, it's also less fragile than a derailleur, and requires much less maintenance. Cycle Monkey, incidentally, is the US distributor of the Speedhub.
Like many of the bikes at the show, the Battleaxe was made to order for a customer. According to Brown, it's worth US$5,000 to $7,000.
Company website: Cycle MonkeyView gallery - 3 images