he said, he was on the small ring and the smaller two cogs, and the chain was rubbing on the back of the big ring.
a big reason for avoiding small+small is, you have more leverage on the chain in the small ring. if you use the small cog in the back, you're putting a lot more force into each tooth of the cog, so you'll eat up that small cog a lot faster.
in general, the bigger the cogs, the lower the friction.
looking at my gear table again...
[TABLE="class: cms_table_mytable, align: center"]
[TR]
[TD="class: cms_table_c0n, align: center"][SUB]front[/SUB][SUP]rear[/SUP][/TD]
[TD="class: cms_table_c1n, bgcolor: #CCFF66, align: center"]13[/TD]
[TD="class: cms_table_c2n, bgcolor: #CCFF66, align: center"]14[/TD]
[TD="class: cms_table_c3n, bgcolor: #CCFF66, align: center"]15[/TD]
[TD="class: cms_table_c4n, bgcolor: #CCFF66, align: center"]17[/TD]
[TD="class: cms_table_c5n, bgcolor: #CCFF66, align: center"]19[/TD]
[TD="class: cms_table_c6n, bgcolor: #CCFF66, align: center"]21[/TD]
[TD="class: cms_table_c7n, bgcolor: #CCFF66, align: center"]23[/TD]
[TD="class: cms_table_c8n, bgcolor: #CCFF66, align: center"]26[/TD]
[/TR]
[TR]
[TD="class: cms_table_c0n, bgcolor: #CCFF66, align: center"]48[/TD]
[TD="class: cms_table_c1n, align: center"]99.8[/TD]
[TD="class: cms_table_c2n, align: center"]92.6[/TD]
[TD="class: cms_table_c3n, align: center"]86.5[/TD]
[TD="class: cms_table_c4n, align: center"]76.3[/TD]
[TD="class: cms_table_c5n, align: center"]68.3[/TD]
[TD="class: cms_table_c6n, align: center"]61.8[/TD]
[TD="class: cms_table_c7n, align: center"]56.4[/TD]
[TD="class: cms_table_c8n, align: center"]49.9[/TD]
[/TR]
[TR]
[TD="class: cms_table_c0n, bgcolor: #CCFF66, align: center"]38[/TD]
[TD="class: cms_table_c1n, align: center"]79.0[/TD]
[TD="class: cms_table_c2n, align: center"]73.3[/TD]
[TD="class: cms_table_c3n, align: center"]68.4[/TD]
[TD="class: cms_table_c4n, align: center"]60.4[/TD]
[TD="class: cms_table_c5n, align: center"]54.0[/TD]
[TD="class: cms_table_c6n, align: center"]48.9[/TD]
[TD="class: cms_table_c7n, align: center"]44.6[/TD]
[TD="class: cms_table_c8n, align: center"]39.5[/TD]
[/TR]
[TR]
[TD="class: cms_table_c0n, bgcolor: #CCFF66, align: center"]28[/TD]
[TD="class: cms_table_c1n, align: center"]58.2[/TD]
[TD="class: cms_table_c2n, align: center"]54.0[/TD]
[TD="class: cms_table_c3n, align: center"]50.4[/TD]
[TD="class: cms_table_c4n, align: center"]44.5[/TD]
[TD="class: cms_table_c5n, align: center"]39.8[/TD]
[TD="class: cms_table_c6n, align: center"]36.0[/TD]
[TD="class: cms_table_c7n, align: center"]32.9[/TD]
[TD="class: cms_table_c8n, align: center"]29.1
[/TD]
[/TR]
[/TABLE]
while I could get 54 gear inches with 28:14, I'm *much* better off using 38:19. or I could get 68" at 38:15, but am better off at 48:19.
Originally Posted by
koolerb
[SUB]Different bike, but to use as an example. I would shift to the big front ring when I get to 4t or 5th on the rear, and then the same on the way back down?
[/SUB][TABLE="class: mytable, align: center"]
[TR]
[TD="class: c0n"][SUB]front[/SUB][SUP]rear[/SUP][/TD]
[TD="class: c1n, bgcolor: #CCFF66"]13[/TD]
[TD="class: c2n, bgcolor: #CCFF66"]15[/TD]
[TD="class: c3n, bgcolor: #CCFF66"]17[/TD]
[TD="class: c4n, bgcolor: #CCFF66"]19[/TD]
[TD="class: c5n, bgcolor: #CCFF66"]21[/TD]
[TD="class: c6n, bgcolor: #CCFF66"]23[/TD]
[TD="class: c7n, bgcolor: #CCFF66"]26[/TD]
[/TR]
[TR]
[TD="class: c0n, bgcolor: #CCFF66"]53[/TD]
[TD="class: c1n"]107.3[/TD]
[TD="class: c2n"]93.0[/TD]
[TD="class: c3n"]82.0[/TD]
[TD="class: c4n"]73.4[/TD]
[TD="class: c5n"]66.4[/TD]
[TD="class: c6n"]60.6[/TD]
[TD="class: c7n"]53.6[/TD]
[/TR]
[TR]
[TD="class: c0n, bgcolor: #CCFF66"]39[/TD]
[TD="class: c1n"]78.9[/TD]
[TD="class: c2n"]68.4[/TD]
[TD="class: c3n"]60.4[/TD]
[TD="class: c4n"]54.0[/TD]
[TD="class: c5n"]48.9[/TD]
[TD="class: c6n"]44.6[/TD]
[TD="class: c7n"]39.5[/TD]
[/TR]
[/TABLE]
With that combination, going from lowest gear to highest...
39:26
39:23
39:21
39:19
39:17 *or* 53:23 (almost same)
39:15 *or* 53:21 (pretty close)
53:19
53:17
53:15
53:13
note the overlap gears with that particular combination are almost the same thing, so in that overlap range, I'd shift up to the big if I expect to keep accelerating, but would stay in the small ring if I know I'm going to be downshifting again soon.
also note that when you shift the big ring in front, you also need to drop several gears in back to get the next evenly spaced ratio.