I have a customized Salsa Journeyman Claris. How small can I go for my small chainring? I'm not sure how to verify compatibility

Question

It's a Salsa Journeyman Claris drop bar 650b converted to flat. The flat and drop frames are the same, but the drop comes with road bike components.

I have already upgraded a Sunrace 11-40t cassette to the rear with the help of a Wolftooth Components Roadlink which leads me to about 20.06 gear inches.

I currently have an FSA Adventure Tempo 30t/46t crankset in the front paired with the Shimano Claris front derailleur but was hoping to drop my small chainring to around 24t for the sweet, sweet, 16.5 gear inches.

Is it as simple as an easy cog swap and a chain? I'm not sure what parts need to be compatible to make it work.

Cheers all!

Answer 1

The crank chainring bolt center diameter (diameter of a circle that passes through the center of the chainring bolts) is what limits the maximum and minimum chainring sizes.

It's likely that you will not be able to get a much smaller chainring on the FSA crank. To get to 24 tooth small rings you need an mountain bike crank. 'Two-piece' MTB cranks made for external bearings in threaded frames or press-fit bearings are not compatible with road frames as they require a wider bottom bracket shell. The FSA Tempo crank is three-piece for a tapered axle cassette type BB though, so you made have luck finding a three-piece MTB double crank with the chainring sizes you want. Bear in mind you will probably have to change the BB as different crank models require different BB axles lengths.

Check that your front derailleur can accommodate the difference between chainrings on the crank you select, and can be dropped far enough down the seatpost.

Answer 2

Three things:

1. Can you mount the chainring on the crank? This is mainly a function of the "bolt circle diameter".
2. Can the front derailer handle the smaller diameter ring? This is a little tricky, but worst case it's obvious, in that the chain guide will be rubbing on the bottom of the top chain segment if the ring is too small.
3. Can the rear derailer handle the increase in chain slack that will occur when on the smaller ring. The rear derailer has a limit as to how many links of slack it can take up between large-large and small-small combinations.

Answer 3

The 46/30 FSA Tempo Adventure crank on the Journeyman uses proprietary chainrings. You presently have no options for smaller rings, larger rings, or other rings.

The small one is an 80mm BCD, which is basically a size FSA made up for this crank. The large one is 110mm but with counterbores on the opposite side from normal, so a standard 110mm ring won't fit.

Going all the way down to 24 once you have a crank where it's possible raises the question of what you'll run for a front derailleur setup. Time was that arbitrarily large tooth count gaps, i.e. 46/24, between small and large on a cyclotouring double were relatively commonplace among enthusiasts, usually on TA or Stronglight touring cranks. In exchange for the wide range, the shifting is clunky. Indexed front shifting doesn't really work with that kind of gap on a double, so no modern systems have it and it's not really seen anymore. If you wanted to go to something like 24/36 on an MTB double, you could do that with an MTB shifter or thumbshifter and double FD with the right specs. There are many questions here that cover the compatibility issues with doing it with your current shifter and/or FD.

If you want to use unorthodox chainring setups and you're staying with flatbar, I highly advise just getting any friction thumbshifter now for your left side and getting used to that. It's cheap, works better than indexed for the most part once you're doing unusual things, and gives you more freedom to do what you want.