I have a Caad9 5 with 105. This chain is brand new. I went for my first post snow ride of the year on Saturday and snapped the chain twice. Once climbing and once on the flat.

It was lubed, in both cases I was not changing gear. I weigh around 200 right now and my legs while not savage, are mostly tree trunks. This is not power related in my books.

Either I have a derailleur issue or the seemingly straight cassette has an issue. I own a quality chain tool that I never leave home with. Chain breakage never strands me.

I bought the bike used and I put a new derailleur/chain on it. This is not the first time the chain has blown up. It took the derailleur with it last time. Should I be looking at the cassette? Looks straight, but we know looks are deceiving.