This tool calculates the complete transmission/drivetrain ratio (engine RPM : wheel RPM) of every gear in a particular transmission setup and the engine speed at any road speed, many gearboxes and transmission components can be selected, or you can manually enter gear ratios of your choice.
Gear ratios are collected from many sources. They are correct as far as I know, please contact me if any are incorrect or if you think there are more that should be added to the predefined lists.