Here is another puzzle.
About a month ago, I replaced my back tire with a slightly smaller one.
I was surprise that the speedometer was totally inaccurate. (I expected a small difference, but not 20 kms at 90 and going all wrong after that).
As I didn't ride the bike for the last 3 weeks, last night I went to the shed to start it. The battery was on a battery tender as I found earlier that the charge was only 12.5 volts. (I was planning to replace the alternator). No problems at all, the bike started fine
This morning was another story.....
Even if the battery was still on a battery tender, it was flat and wouldn't turn the starter.
I installed a spare battery and the bike started on the first push of the starter button.
During the ride (450k), I notice that my speedometer was accurate within 10km at all ranges and up to 150 as it was before (comparing speed with the GPS).
It seems that the low battery voltage was affecting the accuracy of the speedo.
Here is another interesting fact:
This spare battery has not been used for over a year, but was always plugged to a cheap solar panel ($15). It was fully charged!
This is a very cheap battery tender good for the long winter months.
CF