You don't have to be a smart ass.
I made my comment because of yours:
doing a google search I have found that 1 kmh is equal to .6213 mph.
It's as if you said, "I spent 30 seconds on Google and found out that 1 kmh is equal to .6213. You couldn't have tried to research this problem at all."

In response to your current question, of
Why don't you just multiply you km value by 6213/1000? it seems easy to me. maybe I am missing something.
Yes, you are missing something. Did you read my first post?

I can do it the other way where it's 6.21.....Then if the speed is over 65 MPH, it rolls over due to a word sized variable.
Did you ever try to do 98 X 256 X 6.213 on an 18F4550?