What can you do about hard tires?
 

Mine are rock hard on my 123 but they are still in excellent shape with no leaks, with almost full tread. So I hate to spend the money to replace them. But in the Missouri summertime the clay bakes as hard as rock and I get a lot of wheel spin.

I was thinking about using a belt sander of grinder to rough them up. Would that work? When they harden, it is usually on the surface, or all they way through?

Look under this thread. http://www.onlycubcadets.net/forum/s...=soften&page=2 Wild bill give an excellent tutorial on how to do it.

Yep follow Bill's formula and advice and you will have some nice soft tires again :).
Consider filling your tires with fluid too, to add weight at the ground with the tire.