It's going to be a percentage that the speedo is off, not a constant MPH. So I would recommend using a pace car at say 50mph or 70mph. Let them give you a thumbs up at a pre determined speed so you can see what the bike is doing. Turn the difference into a percentage and you'll be able to calculate any speed on the bike.
I hope this makes sence. It's easier to do then to explain. Bike speedo's are off anyway so a chart would have to be make/model and year specific.
If you need any help let me know.
Be sure to use a pace car not pace bike. Chances are that bikes speedo (although it may be stock) is off by as much as 14%.
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Do you really have to start a thread every time you go on a ride and see a guy with no helmet on?
Does it affect you that much that some random guy 1500 miles away went and paid his own money for a 1000?
Do we really have to fight over who uses the back brake or not?
Do you have to argue over stupid pointless shit on the Internet?