Just had a revelation!
 

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.

R u bored :?: :D
I was bored enough to confirm your calcs. lol
well done 8)

Don't worry Northy, I thought it was interesting too.

Not so much for the techie side, but it sounded very much like one of the rambling maths problems I end up doing on long journeys to keep my brain awake.
That one would probably last me most of the way to Scotland...

... I'm crap at mental arithmatic. :oops:

I thought all that was totally obvious? :-dd :lol:


.

That's cunning that is. :lol:

I knew the speedo was corrected, never occurred to me that the odo was too :oops:

Ooh, good photo! Thanks Mr Squid! Cunningly taken from teh side with the undamaged mirror too :)

why does your spedo drive come from the rear wheel?

'cos northy has a GSXR front end :)