2007 VTX1800 F (4.8 gal flangeless tank)
My typical is start looking for fuel stop at about 155-160 miles (low fuel light comes on anytime between 150 and 165), highest mileage I ever had at fuel up was 183 miles during a group highway ride.
As frnkcat does, I always calc my mileage. It gives me a constant way to keep tabs on how my bike is running, watching for unexpected changes. My normal is 39 mpg for city/commute riding, 37 for interstate riding (I'm a bit "speedy"), and usually 42+ for highway riding.
2007 VTX 1800 F Spec 3 - Mustang Seats, Cobra Angled Slashcuts, House of Kolor Blueberry Pearl paint and custom tank badge, lots of chrome, lots of sanding and polishing on the aluminum!
other stuff - HID headlight, airbox decapped plus K&N, ground fix, PAIR/desmog, tail light area minimalized, horn relocation, fwd controls extension, switch spiders removed, reflectors removed, Barnett clutch kit, Cobra FI2000R