Originally Posted by
gregf83
Why does one need to shift down a 'handful' of gears when riding with a 50 but only need to shift a couple of gears with a 42. Seems like it should be the same.
I think one should choose the big ring size so you spend most of the time in the middle of the rear cassette. For me, and many others, the 50 works well for that purpose.
Let me rephrase my concern: you are in a lower cog when in a 50 compared to 42 or 39 (at the same speed), therefore, more likely to run out of gears when downshifting in coming to a stop so you can start up again comfortably.
This means you are more likely to be either cross chained or forced to downshift to the smaller ring. Workable but less than ideal. Neither is likely to happen with a 42 or 39.