The Chimera comes stock with two gun-blue PYC121 half-link chains: a 50 half-link pedal chain, and a 73 or 74 half-link drive chain (depending on chain tension needs during assembly). This pair of replacements includes the 50 half-link pedal chain suited for the stock 34t sprocket, and an 80 half-link drive chain. That will allow you to size your drive chain any way you like for bigger or smaller rear cogs. Be sure to snag one of our Park Tool Ct3.3 Chain Breakers to install.