Originally Posted by
ottovaughn
Sorry, I'm not sure I'm working with the proper vocabulary here to describe shifting.
For shifting with the downtubes, I've kind of come up with my own mental metaphor for what's going on. Basically, I think of the left and right shifters as dueling accelerators - the more the one on the left is pushed down (connected to the front cog), the more the one on the right (connected to the back cog) needs to be pulled back to avoid crossover, and vice versa.
Would you say that this understanding is correct?
Not really, but you're on the Path of Enlightenment.
Bicycle gearing is weird.
The gear ranges between the front chainrings overlap, the extreme combos tend to be duplicates of another gear on the other chainring, and the gear-to-gear progression isn't linear.
For a "normal" road bike drivetrain, with two chainrings in the front with a 10-14 teeth difference between them, and a 7 to 12 gear cluster in the back, you'll need to shift down (easier gear, larger cog, closer to the frame) in the rear when you shift up (harder gear, larger chainring, farther from the frame) in the front to get the next harder gear. For most road doubles, the crossover shift is two cogs in the back, in the opposite direction of the front shift.
So it kinda goes like this, starting in the lowest gear, and using a 2x9 speed setup:
Small ring
1, 2, 3, 4, 5, 6
Shift to the big ring
4, 5, 6, 7, 8, 9
Or something kinda like that.
--Shannon