How to change small chainring I have a bike with a 46/36T crankset (FSA Gossamer Cross BB30) and I'd like to change the small chainring to an even smaller one.

​Googling around ​suggests that the smallest chainring I can get for a 110mm BCD crankset is 33T. Is that right?

Furthermore, it seems that I won't need to replace anything else at all, not even the chain. I run an Ultegra RD-6800-SS rear mech with an 11-28T cassette and all the specs seem to check out:


Max front difference: 16T (in my case, 46-33=13).
Total capacity: 33T (in my case, (46-33)+(28-11)=30).


So just swap out the chainring and good to go, or am I overlooking something? (Never done this before.)

Finally, how do I make sure that the chainring I buy is compatible with my drivetrain? It seems that the BCD (110mm) is all that matters, so something like TA 110 PCD Zephyr would work?

P. S. As I am looking at a picture of the Zephyr chainring, I notice that it says "9/10 speed". What does that mean exactly? (My drivetrain is 11-speed.)

P. P. S. This page lists what looks like the same product as compatible with 8/9/10/11 speeds, but with the following cryptic remark: "For 10-/11-speed drives only with 1 or 2-speed crank handle!" Are they simply trying to say it's too thick for a triple chainset or does this refer to something else?
Most drivetrain setups have a 16 tooth difference between large and small rings. 


Near compact: 52/36
Compact: 50/34
Sub compact: 48/32 


You are trying to get a close to a super compact on a 110mm BCD and will have a chainring tooth difference of 13.

That means the rear derailleur will easily accommodate this as you have calculated.

The front derailleur will also handle the chaining size difference. 

Chain length is set on the large chainring and largest cog sprocket, so you should not have to shorten the chain (assuming your chain is correctly sized to begin with). You will be within the derailleur total capacity so it will take up the extra slack. 

If you do have too much slack in small ring and smallest sprocket, check the chain is sized properly.