I am considering the set up of my next vehicle, I would like some input regarding the pros and cons of the option of 18" wheels vs 20" wheels. I expect to do some rough-roading, logging tracks, etc. in the Rockies where I live. But I will also expect a couple of major cross-country trips (3,000 to 5,000 mile loops) primarily on Interstate routes. What is the difference, realistically, in how wheel size affects the usage? Thanks.