Did my first two tours on knobbies. The first tour included 22 miles of dirt road, but street tires would have been fine as it was very smooth and hard packed. Second one was Pacific Coast. No need for knobbies, I just didn't want to spring for new tires. On the last tour I had Schwalbe Marathons, and they've spoiled me. No more knobbies unless I need them for off road. Next tour (4 more days!) will be on Marathon Pluses.