Not sure what forum to post in but I know most cross read so I will stick it in the Bicycle Mechanics and hope the Touring guys find it.
I’m pretty sure there isn’t a 40t cog out there yet and this is a hypothetical question for the most part. 36t is available in a 12-36 and that is what I’m now running on my touring bike. For whatever reason a lot of these touring bikes come with a road triple up front like a 52-42-30 and more mountain bike gears in the back like an 11-32 (9) The conventional fix for heavy loaded touring is to switch out the triple crank to a mountain bike triple or some of the in between triples. For me the mtn triple like a 44-32-22 was great at getting a super low range but left me not liking the center ring with my gears split between the center and large rings and then not a half step pattern.
It is safe to drop the granny gear on the road triple a bit and I dropped mine from 30 to 26 and there is little issue with that shift from 26 to 42 and no FD changes were required. The back saw no issues with RD going from 11-32 to 12-36.
So my question is if there was a 14-40 available with the tooth count of 14,16,18,21,24,28,32.36,40 and I kept my front of 52,42,26 I would have a total range of 17 GI to99 GI I would have 5 very useful gears off the granny ranging from 17 GI to 29 GI. My center ring would cover a very nice range of normal touring for me of 28 GI to 80 GI. My large ring would give me two more higher gears of 87 and 99 GI and the pattern for the 87 down to say 49 GI would stay in a nice half step. Many say half step is not that important with the 9 speed cassettes and I do agree but these mountain cassettes are wider spaced and I personally like having the in between gears if I can And gives a purpose to the big ring other than one or two higher gears only.
The drawbacks I see are chain length and RD capacity issue. I’m not sure how it would work but I would tend to set it up so the big, big combo wouldn’t self-destruct and the small, small combo would just go slack if needed. I could never see myself going deeper than 4 or 5 cogs off the granny ring anyway. I would say the same for the big ring but I could see that maybe happening when daydreaming or something.
I would think cassettes might last a bit longer with more teeth and yes bigger might weigh a little more. I have played around with all the known sizes I see around and got pretty close to what would be perfect for me with the 12-36. A little bit of this for me is about looks also a very little bit but the bike looked funny when I had that mtn crank on there. I really like the look of the 52. But sure didn’t need a 120 GI on a loaded touring bike.
What do think?