Hi-Center line tires
Hi; I have ridden Ragbrai on a Mtb as do many other people. I think Knobbies are best for off-road and if you do a lot of street riding you have already gotten a lot of good advice about changing them out. For my Mtb I prefer a thinner tire (like 1.25) with what I call a high center, i.e. unseparated ridge line (wow what a description). The single unbroken line runs smooth on the road and the narrower tire rolls fast. I have used slicks which were sold to me as "City Slickers" for street riding in NYC. Good tires, smooth and they really grab the road even in rain. But that came with a price - friction. While they are good tires I always thought they required at least 1 gear lower and were harder to pedal. Find what works best for you.