A few years ago on our way to the NY rally, Snert and I checked this out. He has the larger front wheel on his bike. I was leading and doing 5 mph over the posted limit. His speedo indicated the posted limit. This was on 45/55 mph roads. There is no speedo adjustment to correct this. The general consensus over the years has been that our speedos are off around 8-10 mph at any speed over 40....
So doing 5-10 over puts you in the ballpark.
I'm running an 18/41 sprocket combo btw, and it works for me. I have yet to see a 115 mph road around here.
