Not even going to bother reading all of the (likely valid) replies before I jump in: If you’re a buck-O-five, 32 is fine, if you’re a buck-and-a-half, 34 or 35 should work, if you’re two bills like me, 38 is better and 44 is niiiiice.
Oh, and those numbers are based on my experience with Iowa (township/county/sub-region) specific gravel, YMMV on Iowa B-road, on any change between rural gravel and “Amish/horse-hoof friendly” gravel vs counties without any Amish population.