I have a caliper, that's not going to help. The width of a tire when mounted and inflated is going to be different than what the manufacturers specifies as the "width" depending on what wheel it is mounted on. Trek says 29x1.8 as a safe rule of thumb, but I know for fact you can definitely go much wider than that. Every brand is going to be different, that's why I want to see exactly what other people are running. Trying to eliminate the hassle of return shipping and running back and forth from the LBS with tires that don't fit.