Lots of variables as others have mentioned, but I'll share my experiment from this past weekend. Mine's a 2016 XC with a Madstad 18" windscreen, a 15T primary sprocket, Givi V46 top box and crash bars. Averaging about 80mph near sea level, which is a buzzy 7,000rpm or so with the 15T gear, my fuel light came on with 2 bars showing around 125 miles. It was down to the first bar by 140 miles, and I then babied it to a fuel station at 55 mph, arriving there with 150 miles showing. The tank held 4.2 gallons at that point, so I calculated it probably could've gone 170 miles before being empty, but I'd never trust it past 150 under those conditions. I averaged around 37 mpg on the outbound leg of the journey and 39 on the return. Total elevation change might've been 500 feet. In stock trim it got noticeably better mileage, but I never fully confirmed tank range then.