A method for shifting from a first gear ratio to a second gear ratio in a vehicle is provided. The method includes defining a variable shift schedule comprising at least two gear ratio change parameters. The gear ratio parameters are defined by a pair of engine variables relating to vehicle performance. The method also includes measuring the pair of engine variables to obtain values indicative of vehicle performance for the first gear ratio. The method further includes comparing the values to the two gear ratio change parameters to detect a variable shift condition known to require changing of the first gear ratio. The method also includes shifting from the first gear ratio to the second gear ratio when the variable shift condition is detected.