Stop me if I'm talking rubbish
I've always thought my fuel economy was a bit rubbish... Well, fair enough, 180 jets do drink fuel (same size as what goes in a Firestorm with a K&N!) but it's more than most people report... Why?
Well, I think I've got it. Odo runs from the speedo, my speedo runs from the rear wheel not the front. The height of one side of a "perfect" 120/60 is 72mm, while the height of one side of a 160/60 is 96mm. So, the radius of my wheel+tyre is, in theory, 24mm bigger.
Total radius of the front, then, is 289mm, while the rear is 313. It won't really be that, that's just a mathematically perfect tyre without deformation, but it'll be somewhere in that ballpark.
So, the rolling circumference of the front is 1815mm. The circumference of the rear is 1966mm, an increase of 151mm or approximately 1/12.
So, my miles are 1/12 longer than yours! My average tank range of 120 miles to the flashing light is actually the same as about 130 for everyone else!
(also, the total on the clock is about 1/24th lower than it would normally be, as I've had the rear speedo conversion on for about half the bike's total miles.)
Funnily enough, the "error" caused by running on the rear wheel is almost the same as the error built into the speedo, making it more accurate now than when it left the factory.
Well. I thought it was interesting anyway
If you have a 120/70 front tyre (quick maths here) you fall exactly between the 2.