"Gravel" covers a lot of conditions, but if it were for here, SK all the way-- as we don't have proper gravel. We have sand over clay, clay sometimes on it's own, and clay mixed with sand. If you have something like crushed limestone, either would work. And while SKs certainly don't roll on pavement like a high-pressure road tire, they do remarkably well for what they are. Go as wide as you can in the front. My frame will only clear a 38 between the chainstays, but fits a 43 in the fork with room to spare. That extra cushion in the front is well worth it.
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