As SF lies between the bay and the ocean, the fog and clouds are blocked by the mountains and its nice and warm on the Eastern bay side and rather foggy and cold on the ocean side. Some people even speak of "micro-climate areas" in SF because the weather varies a lot between different different parts of the city.
We biked from downtown SF over to Golden Gate Bridge to Sausalito and visited one of the villages which gave us a nice view on the bay. We rode back and also visited the Golden Gate Park which is a huge park in SF (maybe 2 miles by 5 miles). By then, we were done. Our total distance was only about 15 miles, but since SF is a lot of up- and downhil, so we were even too tired to return the bikes where we borrowed them (6$ extra charge...). But I can only recommend biking SF! It's safe, you get to see a lot more and you don't have to bother with traffic.
