just double checing my LBS
for a loaded trek 520, he's recommending a 48-39-22 triple on the front, an 9 speed 11-34 on the rear. this sounds good to me with an couple exceptions.
He thinks that the higher gearing provided b y the 48-39 big and mid rings will allow me to get in the 'groove' wrt sailing along, and I totally get the point. but does this matter? i keep reading about closer spacing for touring. this combo doesnt look very close. check it out on sheldons gear inch calculator (172.5 crank, 770c 32) .
dropping from middle ring to small ring looks to me like a big drop, IE if using 39 front, 34 back thats 31 gear inches. looks like when moving to the 22 tooth small ring, I'll be racheting all the way to the 23 tooth (three shifts on the cassette) , to get 25.8 gear inches. a little crosschaining and one more click gets me 29.7. thats a lot of clicking on bar end shifters and a full load. i dunno.
my first touring bike and first tour coming in about a week, so i'd like to get as close as I can to 'good'. the 39 mid and 22 small looks to me like a panic wha-oops unclicking of a cleat and a tipsy stop on a steep hill coming down the road.
using a 46-36-22 on the front would make that small ring change require three cassette shifts to get from 28.6 gear inches to 25.8 - is that a 'close enough' drop in gear inches? its closer than using a 36 middle ring and 3 shifts. and doing 4 shifts raises the gear inches so not an option. and only a drop of 1.1 rpm at 80 cadence RPM at the top end.
AND: looks like 44-32-22 is the real sweet spot though (this was recommended in another thread about my tour). WIll it shift OK with (tiagra front der). should I EVER i give a rip about top end?