Originally Posted by
striknein
I recently built a new bike using a compact 2x10 drivetrain(48/34 front, 12-27 rear). I could have gotten away with a 1x10, but I occasionally need to use the 34t ring when carrying heavy loads. Given that, I spend a good deal of time in the big ring, and mostly ride using the 5 largest rear cogs.
Things are pretty much dialed in, but if I backpedal for more than a full revolution of the crank, the chain skips off the largest 2 cogs of the cassette and eventually jams up. When sighting down the chain, I can see that the chainline is way out in the big/big combo.
It appears to me that I can address this issue several different ways:
1) Use a shorter bottom bracket spindle. I can probably get away with moving the crank about 4mm inboard without any ill effects.
2) Go with a smaller big ring in the front. Putting a 46t ring on would probably allow me to spend more time in the middle of the cassette, and I'd be less likely to need a big-big combo.
3) Learn to live with it, spend less time cross-chaining.
Thoughts?
I think you've got it pretty much figured out already.
I use some combination of all three, myself. The crank gets about as short of a BB as I can get away with, since I'm a fan of using the big ring with the whole cassette. And I'll size the big ring so that I don't have any unnecessary gears on the high end that I won't use.
I don't have the issue of popping out of gear when backpedalling, though -- even in the big-big. If I did -- and needed the ability to do this -- I'd probably get in the habit of shifting to the small ring when I'm getting close to the bottom of the cassette, because that would put me nicely in the middle of the cassette again.