Bicycles are still the primary form of transport for millions of Chinese people, although the proliferation of cars and smog make biking in the cities a chore. Large cities like Beijing, Chengdu, Xi'an, Shanghai, and Guilin have well-defined bike lanes, often separated from other traffic. Travel by bike is common in the countryside around places like Guilin, for locals and tourists alike. Locals don't use gears much—take your cue from them and just roll along at a leisurely pace. Note that bikes have to give way to motorized vehicles at intersections. If a flat tire or sudden brake failure strikes, seek out the nearest street-side mechanic (they're everywhere), easily identified by their bike parts and pumps.
In major cities, some lower-end hotels and hostels rent bikes. Street-side bike rental stations are also proliferating. Otherwise, inquire at bike shops, hotels, or even corner shops.