From: marcus.e.helman@gm.com ...<snip>.. "A little while ago I posted asking about gearing theory"..... .."I get the concept of setting things up so that there is not much duplication, but I have questions.
How much difference is noticeable? I can imagine setting it up so that the steps are good, but I have to shift both front and rear each time. Can this be avoided? Does it make sense to set up a reasonable progression for the big ring, and the small ring, and not get hung up on avoiding duplication? What is half-step gearing? Is there such a thing as whole-step gearing? Is there a written source on all this?
Thanks, Marcus Helman Huntington Woods, MI"
The God of Gearing is Frank Berto. He's written just about everything
there is to know about it. I wish I knew where to find an archive of his
works, tho... The next best source for arcane bike knowledge is Sheldon
Brown's web site:
http://www.sheldonbrown.com/
In general, gearing is a matter of personal preference. I find that a 6% step between gears is plenty small. For classic road bikes with a standard double chainring (42-52), I'm happy with two-teeth steps on the freewheel. Most of my classics are set up with a 13-23 six speed SunTour freewheel.
My touring bike (equipped with 25 year old SunTour Cyclone derailleurs) has a triple crank and a 7 speed cassette. It's set up as a "half-step plus granny", meaning that the changing from the middle ring to the large gives a percent gear change that's half of what changing cogs in the back will produce. i.e. changing from the 46T ring to the 49T ring is a 6.5% step, where as changing gears in the back produces about a 13% step.
I'd recommend experimenting on paper and with the cogs. With modern 9 or 10 speed cassettes, the spacing is so close that there's really no point to fiddling around much. With 5 or 6 speed clusters, there is value to getting the spacing right and avoiding duplicate gears.
Steve "can you tell I'm an engineer?" Kurt Peoria, IL