Take a ~1996 Lemond titanium frame, carbon fork, 27mm tires (actual measurement), drop bars, and you wouldn't really call it a gravel grinder, but I did take it on a group ride on the Old Croton Aqueduct Trail in Westchester County, New York. I had the narrowest tires of everyone, and one guy asked me how I dared. I had loaned out another bike with 32mm tires, so this was all I had. I had to stop a couple of times when the trail was very rough, but overall, it wasn't so bad, and I had fun.