uspspro

Hey Tandem Geek,

What ever became of your product testing here?
https://tandemgeek.wordpress.com/2010...belt-vs-chain/

Does Bob manufacture the sprockets?

Did the setup do well beyond your reported rides?

Thanks!

uspspro

OK.. i got to this point.
https://tandemgeek.wordpress.com/2010...belt-update-5/

Looks like a bit of a failure then. Though I'm sure the results would be better with bigger sprockets.

I really like the benefits of the belt drive (feel, quiet, etc), but I like our Da Vinci crank setup.

waynesulak

If belts and sprockets were made the correct size it seems to me that the davinci would be an ideal candidate for conversion with two belts from cranks to common bottom bracket and then a single drive chain. I wonder if Todd at davinci has looked at that option.

Possibly with the center track system requiring less belt tension this might be an option.

twocicle

While we ponder another 27F "Spring" morning and the inevitable decision to ride trainer or hope for the ice puddles to melt and then do an outdoor ride...

As TandemGeek pointed out in "Timing Belt: Update #5", when loading up the front crank that resulted in the bottom run being under less tension than the top. However, it seems the test is flawed as far as tandems go because unless the ubiquitous "she's not pedaling" comes into play, the stoker will also be applying load and thus the bottom run will not be [as] slack. ie: does not the stoker load apply tension to the bottom run?

The other point about sprocket size brings up a question I've had for a while. While it's (more or less) well known that smaller timing sprockets incur higher loads and just require higher chain or belt tension, when the Santana configuration is using larger 74T sprockets, why do they not indicate less tension is required than with the more standard 69T sprockets?

TandemGeek

Does Bob manufacture the sprockets? He has a gates-approved shop that produces the sprockets per his specs.

Did the setup do well beyond your reported rides? Again, you found one of the follow-ups. The 33t sprocket was way too small to be practical. More conventionally size sprockets using the non-bike belts work just fine.

Looks like a bit of a failure then. Though I'm sure the results would be better with bigger sprockets. I wouldn't call it a failure; it merely demonstrated that there are limitations when it comes to pulley size, in much the same was as using chain-drives with very small timing rings can also sub-optimize drive train efficiency and component life.

Two points: I attempted to demonstrate with my locked-brake test just how much elasticity there was along the left side of our Calfee, with contributions coming from frame and bottom bracket axle deflection as evidenced by the lower run of the belt going slack when the sync drive was put under load. However, and as much as we'd like to believe that stoker's match captain in power production, evidence to the contrary can be found on just about every tandem's sync drive timing rings (and now belt sprockets). That evidence is the wear pattern found on the the sync drive's sprocket ramps, which look no different than the drive rings. You can also see it in the different amounts of slack you'll see along the bottom chain or belt run of just about any tandem that you see on the road when they're coasting vs. just riding along vs. climbing a steep grade.

There's really not that much difference between the 74t & 69t in terms of the unsupported belt length, 3/4" top and 3/4" bottom, so the difference in tension wouldn't need to be all that great. But, if you'd really like to be confused by it all, Harley-Davidison uses the same 1" deflection / 10lbs force measurement for the belt drives on their motorcycles.

twocicle

^^^ Interesting. Thanks for the reply to my questions.