http://www.cyclingnews.com/tech.php?...007/news/08-28

Carbon Drive Systems: the next big thing?

If you could have a drivetrain that was lighter, smoother, longer lasting, totally silent, more responsive, and required no lubrication, would you buy it? The folks at start-up company Carbon Drive Systems certainly hope so, and they claim its new system not only offers all of the above but a free cup of frozen custard, too (okay, we're lying about the last part, but that does sound good right now. Mmm... custard).

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.

Spot will offer five CDS-equipped bikes next year, including the Longboard singlespeed 29er, a singlespeed cyclo-cross bike, the Sprawl urban fixie, the internal hub- and fender-equipped Highline commuter, and Spot's standard 26" singlespeed MTB model. Keystone dropouts will be standard equipment across the board, although conventional one-piece dropouts will still be available by special request. CDS also reports that two other companies have signed on for 2009.
Notably absent from the lineup, however, is a full-suspension model. As with any singlespeed drivetrain that doesn't rely on a tensioner, the CDS design is rather intolerant of changes in effective chain stay length as the rear end moves through its travel. While this doesn't necessarily completely eliminate the possibility of a full-suspension rig altogether, it does severely limit the types of systems on which it will work in its current form (dropout issues notwithstanding). Nevertheless, CDS says it has already begun a collaborative project with another well-known builder for a full-suspension model so we'll see where that leads soon enough.
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.
Regardless of those findings, CDS reports that Quality Bicycle Products has already signed on to distribute the system and its individual components. A 'framebuilder kit' will also be available that will include a belt, chain ring, rear cog, and dropouts, and CDS is also open to enquiries from other OEM manufacturers who wish to use the drivetrain.
Currently, chainrings are only available in 32/34/42/44T (effective) sizes and Shimano spline-compatible cogs in 16/18/20/22T sizes. Chainrings are only offered in four-bolt 104mm BCD patterns for now but CDS says more chain ring and cog sizes and patterns are on their way. Retail prices for the chainrings and cogs range from US$38-45, and belts will cost approximately US$60. Further information is available on the Carbon Drive Systems web site.