There are only four reasons to ride a bike on the sidewalk in San Francisco: 1. You're uncomfortable riding a bike in San Francisco; 2. You're drunk; 3. You're a kid; 4. You're chaperoning a kid. The first two reasons aren't good. But the last two aren't bad. And there's no better place, day-in and day-out to pedal along with the wee ones than the flat, forgiving terrain of the Ocean Beach promenade.