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Battleaxe mountain bike features two chains, but very little chain slap

By

March 17, 2014

A close view of Cycle Monkey's wacky dual-chained drive train

A close view of Cycle Monkey's wacky dual-chained drive train

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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.

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.

The Oxide Battleaxe

"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 Monkey

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
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7 Comments

I'm a little confused.

It seems the easiest way to eliminate "chain slap" is to just eliminate the derailer and have internal gears.

I see no means of "chain slap" prevention by adding a jack-shaft.

The only benefit I see from the jack-shaft would be having the ability to raise the suspensions pivot-point while not having to raise the crank's axle height. So in other words, suspension pivots from higher, rider pedals from lower.

Now whether or not that is a big advantage I don't know. I'll let someone with more mountain-biking experience explain that one to me.

anyone?

Milton
17th March, 2014 @ 10:56 pm PDT

Unless the arc of the suspension travel follows a circle with the center point as the pivot (which may of course be virtual), or at least a close approximation within the travel limits, you have what is called chain growth.

This means that the effective length of the chain will change depending on where in the travel the you currently find yourself.

This in turn means that you must have some mechanism to compensate for this change, or the chain will fall off or snap depending on the direction. At the very least, the chain will tend to lock out the suspension completely (personal experience with broken derailler which I had to remove and change the bike into a single speed to continue riding.)

The derailler conveniently serves this function very well. With internal gearing you will still need a small chain tensioner to do this.

The (admittedly slightly overcomplicated and heavy looking) setup in this article appears to move the chain's drive point to the arc center position, which now does not have to coincide with the crank.

It looks like it may allow more freedom in suspension design by letting you choose pivot points independently of drive train while not having to worry about chain growth or fragile deraillers/ tensioners.

This will solve the chain slap problem, but at a cost. Rohloff speedhubs cost around $1200!!!

My wishful solution would also include a Rohloff hub, but paired with a Hammerschmidt front internally geared crank, a belt drive and a small roller tensioner near the front chain... uh... BELTring :-)

Vortexe
18th March, 2014 @ 01:51 am PDT

My first question: is the bike heavier than a normal set up? With a 14 speed hub and extra chain, probably.

Second: Can that not-so-robust looking rear suspension take a real-world beating (lateral forces) on a rough trail? Maybe not.

It sure looks cool though. Would love to try it, but it's too pricey for my blood.

owlbeyou
18th March, 2014 @ 06:00 am PDT

An idler on the pivot is not new or unique, just uncommon. The earliest example I'm aware of is the 98 Cannondale Fulcrum, Welwyn Machine Works has done at least one, custom made with fillet brazed steel, and the Zerode mid drive bikes are conceptually the same. There are definitely more out there.

dreamer.redeemer
18th March, 2014 @ 10:14 am PDT

As Milton mentioned, this has been used already on bikes with high pivot point, one example would be Zerode bikes.

The problem with the system shown here has more to do with the anti-squat, or rather with the means to "play" with its values. This bike will be prone to some degree of sagging when pedalling (not worse than many many bikes on the market), but unfortunately it will be impossible to revert this phenomena as the chain will always be above the swingarm pivot.

Anyways, it's worth being at the NAHBS, but they didn't reinvent the wheel here.

Forest Fab
18th March, 2014 @ 12:59 pm PDT

The primary thing here is to use a geared hub like this Rohloff rather than a derailleur. This allows you to use the short stout fixed gear chain.

Next, to eliminate chain tension problems during suspension movement, simply make the suspension pivot coaxial with the crank. That seems easier than an extra chain and jackshaft that needs to be coaxial with the suspension pivot.

As mentioned by others, the only possible gain with the two chain setup is that you can locate the suspension pivot independently from the crank. However here it is only about 10cm or so away, so I fail to see much advantage possible from this small shift.

Yeah I would love to try a Rohloff hub but they cost more than any of my bikes.

HerrDrPantagruel
19th March, 2014 @ 09:41 am PDT

"This bike will be prone to some degree of sagging when pedalling (not worse than many many bikes on the market), but unfortunately it will be impossible to revert this phenomena as the chain will always be above the swingarm pivot."

Chain line is only one of the factors that determines anti-squat. Pivot location is another. This bike uses a high pivot location to obtain both anti-squat and a rearward axle path. It should also be mentioned that the chain being above the pivot doesn't mean anti-squat can't be adjusted, it's the force vector that matters. Front and rear cog size will still be a factor.

A feature of note that's not shown or discussed here is that the bike is a 29er with roughly a 400mm chain stay length at 0 sag. That is EXTREMELY short for a 29er and is enabled by the rearward axle path. Rear suspension compliance is improved and there will be little or no pedal kickback. These are the things the high pivot provides that the designer is after, not the reduction in chain slap. The downside is reduced pedaling efficiency and weight.

A bike like this can be made without a Rohloff and with a simple tensioner in its place. The real credit here should go to Oxide Cycles for the suspension design, not to Cycle Monkey for adding a Rohloff to it.

craigsj
19th March, 2014 @ 11:45 am PDT
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