With fenders what worth can a tire be on a Salsa Casseroll?
never,never,never give up
It says on their site, but that should be used as a general guideline. It's going to depend on the model of tire and how wide the rims are.
Salsa Cycles | Bikes | Casseroll (Frame Tech tab)
Generous Tire Clearance
Fit 700c x 38mm tires with fenders
Make sure you get 45 mm wide fenders if you want to run wider tires. I've got 35 mm fenders so that would limit me to narrower tires, which is OK because I usually run 28s.
I run 32 Passelas with Planet bike Cascadia fenders with a little room to spare