I made this mobile all terrain dog stairs for my 2 guys. My chocolate lab, Bear is 12.5yrs old with weakening rear hips. My Black lab/Mastiff Bo, is 10yrs old and weighs 140lbd. I had bought a $100 "extra wide" set of steps that was 14" wide. Well Bo fell off of them, and after that was afraid to climb them. I decided to go big. 3ft wide, 18" deep. 5.5" rise per step. Pneumatic tires for all Wisconsin weather. Used My old radio flyer wagon as inspiration for the handle. HDPE plastic for the steps wrapped in all season carpet. 5/8" axle provides all the strength it needs. 3/4" conduit does the rest.