Join Date: Jun 2004
Location: Northern Nevada
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Sussex (which makes shaft drives, and i think developed the one Specialized uses) claims a power loss of "less than 1 percent" vs. "up to 2 percent" for chains. I have no idea if that's true, but 70 percent efficiency sounds very low--I can't figure out where 30 percent of the power would be going, if it's not reaching the wheel. They also claim lower maintenance, no dirt or grease, greater reliability, easier assembly and less noise than a chain drive, but none of those things is a big enough problem on my bikes that I'd change for their sake alone. Gear ratios are limited compared to chains and derailleurs, but there should be a wide enough range for ordinary riding. Their big claim seems to be "smoother operation" vs. the "rough" power transmission with a chain. That may be true on some level, as the links run over the gears, but I've never felt it.
Check it out: http://www.sussex.com.tw/se1.htm
Just based on the little I know now, I'd consider shaft drive if I were commuting, in office clothes, regularly. With that and fenders, you'd avoid most of the dirt and crud that gets on you now. For the kind of casual or training riding that makes up 90+ percent of my cycling, though, I wouldn't pay extra for it.