Hewland gear ratio formulae/ MPH calculations

Hi Guys,



Can someone give me the formula for calculating the MPH for each gear pairing in my Mk9 gearbox? I have a Swift DB1 FF Honda using Hoosier tires.



Also if anyone knows a book or has an excerpt from a book that explains the difference in speed and torque by changing the tooth count up or down on the drive and driven gears.



Does anyone know the circumference of the above tire?



I really want to get a handle on this topic.



Thanks,



Hartley