Friday, October 03, 2008

Thoughts On Belt Drive Systems For Bicycles

<===Spot Brand made it clear to me that they were not "just a belt drive company".

Today I saw a story about Travis Brown from Trek using a belt driven cyclo-cross bike at CrossVegas last week in Las Vegas, Nevada. This prompted me to make a few observations on belt drive systems for bicycles.

I have ridden the belt drive at Interbike last year and I was not really all that impressed. Belt drive is supposed to be this ultra quiet drive train that is smooth and .........well, I don't really know what else. Cool? Different? Yes, I suppose it is those things. I'll tell you what though, it isn't better than a chain drive for mountain biking.

The belt drive system for bicycles is being developed by the Gates Company which does all sorts of belt technologies for motorized vehicles. They were out at Interbike last year en force to answer any questions and to observe first hand a real world demonstration of the "Carbon Belt Drive System" performance. After a quick briefing by the Gates folks, I got on board a Spot Brand bike and took off on the Demo loop at Bootleg Canyon.

On a steep up, I heard a very loud "pop" and I thought I was going to crash because of a belt failure, but I didn't. I rolled on. At the Spot Brand tent, the Gates folks were telling me I "ratcheted" the belt. This is when you essentially get the belt to slip one tooth over on the cog or more. I did that and that was the loud "pop" I heard. With the belt tensions on the verge of being too tight for the bearings on the hubs already, Gates had to go back to the drawing board for a revision for this year.

What they did was to specify a larger "chain ring" and rear "cog" size with a slightly reduced amount of tension on the belt. The larger "cogs" would increase the number of engagement points and hopefully eliminate the "ratcheting" problems. I'm not sure if this also addressed the many complaints of noise in the system from 2007 Interbike riders, but it may have.

The belt drive was again seen at Interbike, albeit a bit more quietly than in 2007. How did it fare? Well, on Day two of the Demo, a rider was seen coming back out of the test loop with a broken belt. Okay, I'm convinced. Belt drive isn't a great idea for a single speed mountain bike. At least not a "conventional" frame mountain bike.

Travis Brown's cross rig addresses some of these pit falls with a beefier chain stay from a tandem bike and whopping, massive eccentric drop outs that are designed to help eliminate flex in the critical drive train area, which should help out the belt in terms of ratcheting and breakage issues. Hmmm...............hey! I've got an idea! How about using a chain drive!

<===The future home of belt drive systems is "here" today.

So, where will all this effort eventually lead us? I believe there is really only one benefit to a belt drive system that will be marketable in the future. It isn't low noise, ( a well lubed chain is nearly silent), it isn't "smoothness" ( a properly set up single speed can be super smooth). So what is it? It is low maintenance and a "clean" drive train. Where does this make the most sense? On commuter bikes. Commuters don't want to fiddle with chain maintenance or have to deal with that greasy thing getting their pants and legs all dirty. Enter belt drive which needs no lube and can be cleaned by a simple spritzing of water. Low torque loads seen by most commuting cyclists would ease issues of "ratcheting" and breakage. Belt drive dovetails nicely in with internally geared drive trains, already a favorite with commuters. What's not to like here?

Belt drive for commuter bikes is a no brainer. Just keep it the heck away from my mountain bike, okay?

It's Friday, so you know what that means! Get out and enjoy some crisp fall riding while the gettin is good!

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