I have a 1996 R1100R that I recently purchased with 17,000 miles on it. Took it to the nearest BMW service shop and had them do a combined 16/24k maintenance that included replacing all fluids, all filters, the plugs, the ribbed V-belt. They synced the TB and tuned and adjusted everything and anything possible. Conti Road Attacks are new with about 1k miles on them, wheels are balanced and true. Brakes in great shape with lots of life left on pads. I've been using 91-93 octane gas. And finally the bike has the stock OEM windscreen.
In theory the bike should be running in top form now, the specs say I should get an average of 45mpg. When I first got it I went through three tanks of gas and averaged low 30's per gallon, Fuelly.com shows people getting no less than 35mpg and as much as 50mpg. With the bike back and tuned I've done two tanks and averaged 25mpg per tank.
Any ideas as to why such low numbers? I commute on the bike so it gets mixed highway and city riding and I'm not a racer, nor do I gun it or rev it high. I plan to take it back to the shop but I'd like to be as informed as possible beforehand so if they try to blow it off I can respond to them.