Most or all motorcycle speedometers are off a little. I found out this weekend mine is off about 2 mph. 10 mph would be a lot but if yours is a little optomistic and your bf’s is a little pessimistic that could add up to 10 mph. Try finding a road that has one of those signs that clocks your speed. Around here they’re usually in construction zones. That’s how I happened to notice that my speedo was off. I always assumed it was anyway but it’s nice to know by how much.