In my sig there's a whole section dealing with my problems with 27" wheels. They don't make good rims in that size anymore (though you might find a used one that's strong) - I don't know how heavy you are but I'd say if you're north of 260 you may want to start looking into replacing them with 700c (borrow a 700c wheel from your lbs and see if the brakes will reach (extra travel in the arm)).