Fonk

I was thinking about setting one of my bikes up w/ a standard crankset (53/39), but may want to swap it out with a compact (50/34) now and then for different types of riding, terrain, etc. So my question is - is the difference between the 53 and 50 chainrings big enough that I'd have to worry about the chain possibly dropping over the large chainring if I don't bother lowering the derailleur after swapping the cranks? Or is the difference small enough that I don't have to worry about it?

Thanks.

joejack951

You will need to lower your front derailler to use the compact. If you did manage to get it to shift into the big ring ok, you'd probably drop your chain on every downshift still. The difference in outer diameter between a 53 and 50 is more than you think. I was surprised when I saw it on a bike that I installed a compact crank on.

Fonk

Yeah, I was afraid of that. Thanks for the reply. Assuming using the same cranks (like both FSA Mega Exo, or both Shimano Hollowtech, etc.), there at least shouldn't be much of a need to mess w/ the limit screws though, right? Pretty much just lower/raise, and I'd be set?

joejack951

You shouldn't need to tweak the limit screws but you might have to anyway (tolerances can add up causing assemblies that should be identical to not install quite the same). You will also need to undo the cable pinch bolt and remove some cable slack that will result from lowering the derailler.