In my experience, thursday nights tend to be a fiercely contested social timeslot. Whether you're a college student that starts your weekends a day early, or participate in the typical Silicon Valley practice of "work-from-home-fridays", Thursdays always seem to be a good day to start unwinding and focusing on the "life" portion of that critical work/life balance.
One of my favorite ways to ease into that chill zone is with a nice bike ride, and big beer, so the Stammtisch Ride from Rapha to Biergarten is a perfect fit. It kicks off every Thursday at 6pm from the Rapha Cycle Club in the Marina, rolls through some of the most scenic roads and trails you can cover on 2 skinny tires, and finishes off around 8pm with a big beer and burgers/brats at Biergarten in Hayes Valley.
Though the route changes on a weekly basis, it always includes a healthy smattering of exploration and adventure. You'll be happiest on a road or cyclocross bike, equipped with some larger tires. Not to say that it couldn't be done on 23mm slicks (and there are always many that do!) but I'm of the opinion that you should always use the best tool for the job. For me, that usually entails riding my Hunter Bicycles cyclocross bike and 35mm knobby tires.