Originally Posted by
Princess_Allez
The drivetrain is all fairly new. It has ~1500 miles on it. It's all the factory stuff that came on my 2018 Specialized Allez Sprint.
So the takeaway here is that I can go 11-30 without changing chain or rear mech, but if I want to go 32 or 34, then it would require a new chain and mech?
The takeaway is that we don't know how the chain was sized originally because there are a few different ways to correctly size a chain. Since it is a KMC chain you can test it easily by installing the new cassette and wrapping the chain around the big front cog and big rear cog and see how much excess chain there is for your desired cassette. The rear mech is generally conservative so an 11-32 should work fine on a short cage mech and possibly even the 11-34.