I consider the bicycle to be one of man’s greatest inventions of all time. Why? Because in more than a century of its existence, the bicycle is essentially still powered by a chain and cog. If there were a better, more efficient way to power a bicycle, companies like Shimano would have already figured it out.
But the folks at Gates aren’t convinced a chain is the best way to drive a bicycle. Although a patent was filed in 1890 for a belt driven bicycle, since then, the challenge of making the belt stiff enough to not flex or break while staying on its track has proven elusive.
That is until industrial belt drive pioneers Gates Corporation developed the original Carbon Drive System in 2007. Although plenty stiff, the original Carbon Drive System still had issues with alignment and staying on its track. In 2011, Gates released the CenterTrack and CDX systems, featuring a groove down the center of the belt which lines up with machined fins between each chainring and cog tooth, keeping the belt perfectly aligned while requiring less system tension.
The Gates Carbon Drive belt is made of stretch-free carbon fiber tensile cords covered by a weather-resistant polyurethane outer. Although the belt is remarkably strong, bending, crimping, and/or twisting it the wrong way can bring it to a premature end. Even transporting it improperly can do damage–Gates prescribes a particular coiling of the belt to prevent damage to the carbon fiber cords should you need to carry one.
And though you may be tempted to use the belt as a chainwhip to remove a Gates cog, don’t. This too is belt killer. Use a strap-type automotive oil filter wrench instead. It works perfectly.
Like any new kind of technology, the Gates Carbon Drive system takes some getting used to. First off, all the gear inch calculations you’re already used to with chain driven systems get thrown out the window. Instead of familiar gear ratios like 32:21 and 34:19, you’re dealing with oddball numbers like 46:28 or 39:26.
And because you can’t cut and adjust the length of a belt like you can a chain, once you figure out the proper gear ratio, you’ll need to order the correct belt length. Measured in number of teeth, the CDX belt comes in eight different lengths.
Because each gear might potentially use a different belt length or at least require an adjustment in the frame tensioning system, easily running a “dingle”speed option – two different gears that run the same chain tension—is pretty much out of the question. Not a deal breaker for most buyers, but something to consider nonetheless.
Another minor annoyance with the belt is figuring out how much tension to run. There’s two ways to properly measure the tension—a Gates tension meter or the Gates smartphone app. Because the app is free and with me whenever I have my phone, I downloaded it and gave it a try. The app works by listening to the tensioned amplitude of the belt when you pluck it like a bass guitar string. It shows the recommended Hertz range and tells you at what frequency your belt is vibrating.
Although a pretty slick idea, I could never seem to get three consecutive accurate readings from the app. And further, my belt tension always seemed lower than what the recommended tension was. Because I was running the Gates system on my Ibis Tranny 29, the frame tensions by telescoping behind the bottom bracket. I literally sat my entire body weight on the bike to tension the rear triangle, cinched down the Slot Machine bolt on the Tranny 29, and I was still below the recommended tension.
After that I gave up and simply took a rather unscientific “tight enough” approach. It’s worked fine for me with no slippage at all, so I’ll just stick with it. The app does have a few other handy features though, including a complete product catalog of all cogs, rings and belts as well as a calculator to figure out specific gear setup so you know exactly what ring, cog and belt to use.