rdavid makes one very good point, and I'll repeat it here in my own words: It is almost always about the tires. What I've learned from riding early rigid-framed Harleys and driving lotsa different stuff - logging trucks, Jeeps, Harleys etc. - on bush roads hereabouts is that tire construction and pressures are absolutely crucial to handling characteristics. Forget what it says on the sidewall: That is for full-load smooth highway high-speed driving in very hot weather. Anything else requires lower pressure, and depending on conditions, what will work best is probably a lower pressure than you'd think.
Radials in 33/12x15 sounds okay. I have 235/85R16's on mine, and when I'm empty on a rough road I'll run between 30 and 40 psi in 'em. With a full load they'll get twice that. I don't have tire failures because, as hard as I make them work, I watch them carefully under weigh. If they get too hot I'll bump the pressure. If they ride too rough I drop it. If it's both, I'm driving too fast for conditions. Once I started sinking into soft sand and I dropped the pressures to 9 psi. No, I did not leave them there after I drove out. On a logging truck I ran I could change pressures in the drive tires as I drove, from the cab.
