More Hype: 30-Speed Bicycles
Mood:
chillin'
Topic: Cycling
With the advent of modern 10 cog freewheels, the "30-speed bicycle" has become a reality. Combine a triple chainring with a 10 cog freewheel and you've got 30 speeds, right?
Well, maybe . . . and maybe not. Chances are some of the extreme combinations (i.e., large chainring/large freewheel cog) may not sit too well with even the most modern derailleurs. Assuming your state-of-the-art "carpet-fiber" shifters can handle the extremes, are the gear-inches produced unique or just near-duplicates of some other chainring/cog combinations? Is the resulting shift-pattern too-complex to master even with a gear chart taped to your handlebar stem? (Ah, do you even understand what I'm talking about?)
To quote the late great cycling sage, Sheldon Brown, "(gear inches) . . . is the equivalent diameter of the drive wheel on a high-wheeled bicycle. When chain-drive "safety" bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two-or-three-digit number."
So . . . do you have a clue what the available gear-inches are on your 30-speed wonder? How about the shift-pattern you need to use to get the most use out of all your gears? You can use Sheldon's handy on-line "Gear Calculator" to figure our how your available gears plot out, then pray that you don't have a bunch of wicked double-shifts (shifts on both derailleurs) needed to use your gears.
For the record, my 1980s-vintage Ciocc (which has 52x41 chainrings and a six-cog 13-23 freewheel) has eight very useable gears with only one double-shift. Four up on the rear derailleur, one shift one the front derailleur to the big ring and one back on the freewheel, then three more on the rear derailleur to top out. Reverse sequence to shift down. Easy to remember and very quick - important in a race when you can't be fumbling to find the right gear.