Or, just borrow someone's portable GPS (LOTS of folks have them these days) and have it save your maximum MPH. Then you can check the GPS, Honda and V-Rod. I've seen several Honda's that are high (never low) on the speedo.
You can also (with a stopwatch) check your speed easily using mile markers. At 60 MPH it will take EXACTLY 1 minute to travel a mile. If it takes LESS than a minute, you are going OVER 60. If it takes MORE than a minute, you're going under 60. Simple algebra will tell you how far off you are.
(For the V-rod, at 120 MPH it will take exactly 30 seconds to cover that same mile... but you get the point.)