+1 for the Rans Screamer. We have had ours now for 8 years and have used it for day rides and extended touring pulling a BOB trailer. Our team, plus the loaded bike (water bottles and panniers) would be more about 400 lbs. We run a 20x1.35 Schwalbe Marathon Plus on the front and the same tire, 26x1.5 on the rear. Biggest challenge we faced was transporting it to and from rides. Settled on a Draftmaster which works great. Have hauled the bike from Canada to Florida and back 5 times with no issues.
Mike