I don't have thunder calves...I tryed them on around the store, size 28.0, and I like the fit of the boot...When I got back to my apartment and was walking around for a while in them, it seemed as if they were suffocating my calves. I'm sure they need to be broken in a little bit, but they shouldnt be THAT tight. Would bumping up a size make a differnce. a 28.5 is the same shell as the 28.0...What do you guys think?