My Mum and I have been asking ourselves this question for a while (ever since I started riding), and since there is such a wealth of intelligence amongst the members here, I thought I might be able to find the answer for once! Mum rides a 2003 Kawasaki VN800 Vulcan Classic I ride 1998 Suzuki Across 250 We both fill our tanks at the same time, at the same place, and reset our Trip Computers back to zero. We travel to exactly the same place, usually me riding in front, at pretty much the same speed, and stop at exactly the same servo... Our Fuel usuage is almost identical (give or take 1-2 km's/L difference)... My bike uses LESS fuel than Mum's 800..... The problem? Mum's bike ALWAYS travels at least 5 km's further than mine (over a 100 km trip)! :?