Wednesday, October 31, 2007

The new 'shebang', viable or not?

Just a word or two about conventional roller pin chains. They are one of the most versatile of power transmission means, and have an efficiency of anywhere from 94 to 98%.

Carbon Drive Systems, however, aims to "replace" conventional roller pin chains. Why? So it resists "stretch"? The bicycle is perfect as it is, its a wonderful machine, it looks even better with a chain for me. It offers a lot of options for one to change gear ratios, and you can use them on multiple bikes. So when CDS comes out with a design like this with so many imminent restrictions, I am taking their whole idea with a lot of salt.

1. Having carbon fibre, a fatigue irresistant material for a chain is a whacky idea. Belts with CF can snap right?

2. Theres a marginal decrease in noise in belts. As far as cleaning and maintenance goes, belts may win hands down. But it takes a man to ride a bike with a chain, and handle one. Stop wussying...

3. It would take a comparitively wider belt to equal the strength of a chain.

4. Chains are idiot proof. Chains don't slip.

5. Belts could be expensive, this would offset the slight advantages they might have. What about a mass market for this thing?

A cycling news article carried the following about the shebang (not really sure where this word originates or what it could mean).

The system is built around a 52g toothed 'polychain' comprised of multiple strands of stretch-resistant carbon fiber embedded in flexible polyurethane. The matching proprietary chain ring and cog are made from CNC-machined aluminum, and the whole shebang weighs just 180g (yes, we said "180g," and no, it's not a typo. Read it again if you must).

The embedded carbon fibers are also said to transfer tension faster than conventional roller pin chains for more immediate response to pedal inputs, and CDS even claims belt lives up to 10,000 miles for its 'endurance' model (a smoother running 'performance' system supposedly offers only marginally shorter lifespans). Gaping ports in the troughs of the cog and chain ring teeth also appear rather capable of evacuating even the nastiest goop, and after eight iterations of design refinement, CDS is confident in the final product.

So what's the catch, you ask? The system will almost certainly be forever limited to fixed-gear or singlespeed applications, and the belt currently cannot be separated and respliced so you probably won't be able to use it on your current rig very easily. However, CDS is working with singlespeed maverick Spot Brand to bring the system to market on a wide range of bikes thanks to a clever 'keystone' dropout that allows users to easily split the drive side chain stay and seat stay with virtually zero visual indication that it's anything out of the ordinary. The dropout is only made in steel for now but CDS says titanium and aluminium ones are imminent.

One question left currently unanswered, though, is that of drivetrain efficiency. Conventional roller pin chains are also among the most efficient drive systems on earth, and it's difficult to imagine that a polyurethane belt and its seemingly obvious hysteresis effects can improve on that. CDS is optimistic nonetheless, however, and is currently undergoing third party tests to confirm (or refute) its claims.

Non lo so. I'd be very interested in some test results from any third party guys.

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