I have 19.5" on my 93 Airstream I have put 80,000 on the coach myself with 2 sets of tires 1 set still in use I have air/hydraulic braking and disk brakes all around the back brakes changed this winter at the 98,000 mile mark. My ride is good and I have changed the shocks to Bilstien about 30,000 miles ago. My coach weighs in at 21,000 loaded checked on the scales. So if I had 22.5's on her how much further would I go ? I know the weight might affect the MPG and I do not think it would roll out any better. This is a Spartan Chassis so I think they probably spec'd out the tires. I have to agree that sometimes the body looks a little big for the feet. All those miles and places and good brake and tire results I think I have truly saved a good deal of money over the last 21 years.
