Well she was behind me for mosr of the trip so she might have done that!

So if your friend’s odometer reading is lower than yours for the same trip his odometer is more accurate than yours. [/quote]

Lynn's a girl's name in this country Larry ;);)

Fascinating to see those statistics.

And Nelly, your explanation seemed equally valid - as always! :lol:

If you do the math you can see that a trip of that distance can easily have a reading difference of 1 or 2 miles with just a difference of 2/10 of an inch in tire diameter. All other things being equal, i would think the difference in tire wear accounts for most of the difference (except for those wheelies she may have been popping!). Play with the numbers yourselves and see what a difference a 10th of an inch makes over 50 miles.

Mad Dog, i'll leave the maths to someone else, its not my strong point which is why i asked the question on here!

So after 20,000 indicated miles, her bike might only have actually done 19,000. Thats quite significant isnt it??

With tire wear and other mechanical events taken into account, that (5%) would not be so unusual and in fact may be a fairly good accuracy for all those miles. Rally cars, even for amatuers are equipped with much more accurate speed and odometers because of the inherent problems in normal civilian stuff. Just think how much difference low tire pressure would make (again, plug in the numbers). Even my mountain bike has adjustments for actual tire circumference instead of tire size as over a few thousand kilos there is a noticeable difference. Ask Lynn to keep the front wheel on the ground!

Thinking about this made me realize that just small deviations in tire molding would make the speedos differ between similar bikes, but I think Shazzam needs to do another erudite post on the matter!

It could explain why the fork seals keep going!

I know the terratrip things on rally cars be be set with the rolling radius of the tyres there are using.

That is why even amatuers check their tire pressure with digital gauges and do a look at their actual tire circumference. Small differences can mean missed check points even over small differences.
As for the fork seals, just put an 18 tooth front sprocket on.......great for mileage and saves forks and frames as well.....heh, heh

Excep that over longer distances it will average out between you because you will have both been through several sets of tyres from new to worn.

No need to go through complicated maths or averages to get a big difference between indicated and actual mileage. My speedo cable broke at 14,827 miles and now, some 3,000 miles later it's still reading 14,827 :lol::lol::lol: