Why BWM gave the R1100S a fuel tank the size of a Methodist's Bladder is beyond me. I picked up the 'Drilling' mod from the BMW Club site. Drill a 5mm hole towards the top of the gold coloured cup in the fuel aperture (removing it first). It means you can actually fill the tank to its full capacity without creating an air-pocket towards the top of the tank. Now getting an extra 20/25 miles before the yellow fuel light. Since I swapped the dodgey rear shock,.. the seats now comfy too, .... so 'Blue88's in high cotton.
Geoff