GearCalc

GearCalc is a program that calculates theoretical maximum speeds in each gear and speed per 1000 RPM (revolutions per minute), given the maximum RPM of the engine (redline), the gear ratios, tyre size and the differential ratio.
It also produces a chart of RPM values for every 10 Km/h increment in metric mode or every 5 MPH increment and gear up to the redline. Finally, it also calculates the rev drop at each gear change.
Entry of tyre size can be in the 185/70x14 style, which will then automatically calculate the diameter and circumference, or if the tyre is not marked in this style of sizing, actual measurement of diameter or circumference (the most accurate method) can be entered.
The user should be aware that the maximum speeds calculated here do not take into account wind resistance. Often, a vehicle will not achieve the calculated maximum speed in top gear as there is insufficient power to overcome wind resistance.
GearCalc can assist with choosing an appropriate gear set to maximise performance. The program includes a lot of gear ratio presets for cars such as Honda Civic or Mazda Miata.