I'm a little surprised how high the 'minimum' numbers in this thread are. I like wider tires too, but I'd say my minimum is 27mm since I've ridden lots of gravel roads in Colorado and now in California with trusty Parigi-Roubaix tires and always been happy with them. Maybe that's in part because I got used to riding a CX bike with 28mm tires on singletrack? Last week I was out exploring the area around my new home and found a farm road that suddenly turned into loose chunky golf ball gravel with washboard for a couple miles - I was on my go-fast road bike with 23mm tires and plowed through without incident even though it wasn't much fun, so maybe 23mm is my real minimum?