Using triple shifter for double chainrings
 

I am currently running a modern Deore 48/36/26 crankset with a Deore front derailleur and Deore 9-speed trigger shifters. I have never used the 48 ring so I want to remove it and then replace the 36 with a 40t ring. The resulting 40/26 crankset would be paired with a 12-34 9-speed cassette.

Can my current Deore triple shifter and front derailleur be made to work with a double crankset? Can a good mechanic set it up so that the most outward click isn't possible and I can safely shift back and forth between the middle and inner rings without fear of throwing the chain (without a chainguard)?

It should work. I've got my wife's bike setup with a set of 9 speed (triple) shifters on a 46/34 cross crank; shifts like a dream. Just adjust the limit screw such that it doesn't go beyond the second ring.

As Bentley referred to, the only thing you really need do is adjust the limit screws on the front derailleur so that it can only go where you want it to.

As long as the lever and FD match, you're basically home free.

The only potential issue is the specific chainring combination, and the height of the FD. First of all your larger ring is only 40t and the curvature of the FD is matched to something in the 46-48t range. That means the cage won't follow the contour of the ring, and will be farther away at the bottom. If it's a braze on, you also may be limited in lowering it enough.

Lastly the cage is highly sculpted to make ramps based on 10t chainring separation and a height close to the top ring. If you get sub optimal shifting, feel free to adjust the height to get the ramps where they work best for you.

All of those minor issues should be manageable, and I doubt will severely affect function. They may make it slightly less than perfect, so my post is more by way of telling you where to tinker as you try to optimize shifting.

One other option, should the 40/26 not work smoothly or well enough, would be to keep the 36 and 26 as-is and install a ~44T biggest ring. A 44/12 top gear would only be about a half-step bigger than your proposed 40/12, and the FD would almost certainly handle it fine. :thumb:

Thanks! I didn't know if the FD has enough adjustment to keep it from going past the second ring.

I plan to basically ride all the time in the 40t ring and just use the 26 for a bail out granny gear. Worst case scenario, I'll just put an old fashioned friction shifter on the front if the triggers require too much tinkering to get smooth.