Originally Posted by boyze

I believe the advantage might go to the chain ring change because you will impact more gears. If you have a 9 cog cassette and can use 7 cogs for each front ring then a ring change affects 7 gears. If you change a rear cog and it's useable by 2 front rings then you only affect 2 gears. If your desire is to only affect a low or top end gear then the weight advantage goes to changing the rear cog. Cog wear I suppose is a consideration but unless you're a one cog rider I believe that's secondary.