From: cortesi@helium.informix.com (David Cortesi) Date: Fri, 23 Oct 92 11:07:08 PDT Subject: what about toothed belts, then? Somebody on GENie was asking about hydraulic motors so I guess I can't look any sillier asking: what about toothed belts? Clearly a toothed-belt derailleur would not be practical. (Would it?) But for non-shifting links, for instance the front half of an "intermediate drive" or the front crank of a tandem, wouldn't a toothed belt be lighter than a chain? And cleaner and quieter? There's no problem of strength, longevity, or dimensional stability, not when toothed belts will drive the overhead camshafts of a car engine for 50,000 miles. So are there big friction losses, or what? Dave (still commuting head-first) Cortesi cortesi@informix.com From: " pardo@cs.washington.edu" Date: Fri, 23 Oct 92 13:49:20 -0700 Subject: Re: what about toothed belts, then? >[What about toothed belt drives? Durable? Drive cars K's of miles.] The car belts work in a pretty clean environment, so there's no guarantee you can extrapolate to bike use. Luckily... they do work in the comparativly dirty bike environment. In particular, check out the Bridgestone Picnica folding bike. They use a clever (prob. patented) device to ensure that the harder you pedal the more the belt gets tentioned. That's to ensure it won't skip, even though it's pretty elastic. I don't know what the Harley's do, but the % friction losses are much smaller when the absolute power is much higher, so they may just tighten 'em up. What's the efficiency for a bike? Sorry, I don't know. ;-D oN ( Lost at efficien sea ) Pardo From: richard@pegasus.com (Richard Foulk) Date: Fri, 23 Oct 92 14:55:54 HST Subject: Re: what about toothed belts, then? I've been curious about this myself. Many years ago I bought plans for a one-man hovercraft from Popular Science magazine. They specified that the two ten-horsepower engines could be connected with chains or timing belts, but that the belts were more efficient. Their numbers were 75% efficiency for the chains, and 90% efficiency for the belts. I have since seen claims (on the net) of 90%+ for bicycle chains. What's the scoop here? Some small helicopters I've seen are belt drive also (perhaps due to the ability to stack multiple belts side-by-side for redundancy). Richard Foulk richard@pegasus.com From: SteveSgt@torrent.sj.ca.us (Steve Sergeant) Date: Sat, 24 Oct 1992 10:54:38 PDT Subject: Re: what about toothed belts, then? Most of the 'ordinary' commuter bikes I see when I go to Japan are single-speed, front-caliper and rear drum (band) brake, belt drive bikes. The belt drive is considered more maintanence free and reliable. But efficiency is not such a big issue for them; reliability is. These bikes have a a bit of spring-loaded shock absorbing give in the crank pulley to protect the belt from high instantaneous forces. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Steve Sergeant Internet: SteveSgt@torrent.sj.ca.us 3266 Tulipwood Ln. Radio: KC6ZKT [@N0ARY.#NOCAL.US.NA] San Jose, CA 95132 GEnie: STEVSERGEANT (408) 945-0395 FAX: (408) 945-0543 Audio Engineering, Music, Macintosh, Bicycles, Backcountry, Japan