Now this is an interesting discussion.
I also have a portable GPS. I haven't checked speed with it, but now I'm going to make it a point to do so.
I too have passed those police radar checks, but they have never matched my indicated speed. They have always shown less than what I'm indicating - sometimes more than 5mph less. As a result, I have been wondering if my speedo is accurate... One thing I was thinking is that perhaps because the profile of the bike is so small, that it can't get an accurate reading. Anyone have any thoughts on this?
I'll try to post my GPS results here too, to add to the data....
Kenny