Probably a dumb question. Have a FSA 54t outer ring. Ideally don’t want to go with a 42t inner chainring. Will a 39t work with the larger outer ring?
I have a 55 outer and 39 inner, it “works”… The front derailleur needs to be adjusted slightly depending on where I am at on the cassette… might not be good on a road bike but on a tri bike it isn’t bad because you can adjust the front derailleur pretty easily with the bar end shift. I just installed it though so I have only ridden about 100 miles or so with this setup so far.
Yes, and it works a bit better with a SRAM chain. The Shimano chain design works much better with the Shimano pickup ramps and pins as they are beveled on the edges. You adjust the F-Der just as the other post said - many folks like to set the limit screw to over shift a bit, but then you can risk tossing the chain out.
As noted, it “works” but, depending on your front derailleur, it may not be in spec. Shimano FDs specify no more than a 14-tooth difference between big and small rings, and 54-39 is one too many. That said, I ran a FSA compact crank (50/34) with a Shimano FD with no problem for years. Now Shimano even sells their own 50/34 compact crank with some suspicious words about their 16-tooth delta being “special” and okay with their FDs. Not sure about Campy or SRAM, but if you have Shimano you’ll be okay.
Probably a dumb question. Have a FSA 54t outer ring. Ideally don’t want to go with a 42t inner chainring. Will a 39t work with the larger outer ring?
That’s what I currently have on the crankset I use on both my road bike and TT bike. It works just fine. The only thing you might notice, and this is only apparent on bikes that have short chainstays (like both my Soloist and P2K) is that when in the 39 and some of the smaller cogs, the chain will “tickle” the teeth of the 54T ring. No big deal…I think of that as just a reminder to shift to the big ring 
No issues - I have an FSA Chrono that came as a 54 / 42 and I went to a 39. It is set up on a Guru Chrono w/ Dura FD and chain. Been working great for over a year.
Probably a dumb question. Have a FSA 54t outer ring. Ideally don’t want to go with a 42t inner chainring. Will a 39t work with the larger outer ring?
Yes, I am riding 57/39 (edit: and I have ridden as much as a 63/39 without much problem).
Probably a dumb question. Have a FSA 54t outer ring. Ideally don’t want to go with a 42t inner chainring. Will a 39t work with the larger outer ring?
Yes, I am riding 57/39 (edit: and I have ridden as much as a 63/39 without much problem).
Sorry to bring this topic back from the dead: I just got a 60/39 (only because I couldn’t locally find a bigger inner chainring)… this bike is purely for use on my trainer anyway, but just wanted to know what Front Derailer was used for the 63/39, and if there are any things that I should watch out for when doing a 60/39 combo?
EDIT: The 60T is not “mine is bigger than yours”… I keep it on the trainer for those low cadence (30-40) work… (my roadbike has the standard 53/39)
I still need the small chainring for those recovery pedaling times…
Where do you guys get the really big chainrings? 58, 60 etc.
Big inners too.
Does anyone make stuff for 10 speed that has ramps and pins?
I’ve run that setup with pretty good success. On my bike (Scott Plasma) without any tension on the chain,
such as in a bike stand, it will hardly shift from inner to outer. On the road it was a non-issue 90% of the time
and I would occasionally get a balky shift. You will need to play with your FD up a little bit to adjust it for bigger
circumference of the 54.
Any minor gear grinding it worth it for the top end speed on a hilly course…
.