September 27, 2012

DIY Gates Carbon Belt Drive Tension Tester

Violet utilizes a Gates belt drive to power her single gear. I love it and the technology that it utilizes, not that there hasn't been belt drive bicycles decades ago, it is just the simplicity that caught me hook, line and sinker. The belt drive is touted as being nearly maintenance free. The use of the word "nearly" is applied liberally. True, you do not need to lube it and it is supposedly stronger than a chain, but you apparently can't twist, pry, bend back, bundle, crimp, invert, or even look at it or it could be damaged (OK, I made that last one up). I understand that the belt was meant to be used in one direction, since it was produced to be strong in the direction. The tricky part is getting the tension right by adjusting the special rear dropouts that are present on bikes using the belt drive. Too high tension and you can't pedal; too low and the belt literally pops off the rear sprocket when ragging on the pedals, making a God awful sound. They (Gates) do offer a handy, idiot proof tool that you just press down on the belt and it tells you if the tension is too high or low. Said tool is $40. I am cheap. Therefore, I winged it the last couple of times I made adjustments. The belt would seem fine for awhile, but I would inevitably slip going up a hill and have to take SWAG on the rear drop outs. In other words, I new I was doing it wrong and had no one to blame except Gates for not having a cheaper tool. Just kidding. They do have a cheaper "Eco" tool that hangs off the belt, but thanks to the fine folks at StackExchange I decided to make my own. It consists of a 21 mm to 114 mm hose clamp (useful for all sorts of things!), two S hooks, and a 10 pound steel plate with some wire. I just separated and flattened out the hose clamp so that it was like a thin oval, attached it around the belt, added the S hooks and 10 pounds. The ruler is taped to the frame and measures the amount the center of the belt moved after attaching the 10 pound plate. Before adjustment, it was 14 mm, out of spec. I adjusted it to 10 mm and, boom goes the dynamite, the belt is perfect. One last note on the "carbon" belt drive. People ask what it is made out of, and me, a former student of polymers, always bungles it. The belt is polyurethane, not rubber, and it is carbon reinforced, not carbon fiber like some bike frames. No one know what polyurethane is, so I am going to go with "carbon reinforced polymer composite." That makes them nod their heads.
bicycle on a chair and books with a belt drive tension tester set up