The rim width of the rear wheel on the Yamaha FZ series motorcycles can vary depending on the specific model and year. However, in general, the rear wheel rim width for Yamaha FZ bikes is typically around 3.50 inches. It's worth noting that different FZ models may have slight variations in rim width, so it's always a good idea to consult the owner's manual or contact a Yamaha dealer for precise information about your particular FZ model.