So a couple of months ago i put a 16 tooth front sprocket on my FZ1s so i took a satnav on the tank pad to check out the speed correction.
I found the bike to be over reading as expected , the speedo read 44 to satnav 40 ,speedo 55 to satnav 50 and so on, so there is a 10% over read, easy to calculate when riding.
I got the speedo to read 142 and the satnav recorded 128 max speed of trip.(on a closed airfield of course)
On my Hilux pickup the sat nav reads slightly less than the speedo for cross reference,50 on the speedo and 48 on the sat nav so that 4% is my safety factor on riding at speed limits.
SO as written about the sprocket change making a 5.4% over read and the inbuilt 5% over read on the bike speedo i know where i am.
And as for the 16 tooth mod well, i takes away the need to change down to over take ( in most cases anyway) and makes for a smoother ride.
I have recorder 130 miles on the milo and the fuel is flashing ,so have to check what is left in the tank as i want 150 miles to the tank or if not then the 17tooth is going back on.
Four of us are riding to Mugello end of May, going through Switzerland , my mates gsxr 750 needs to stop at 150 miles so should be ok.