Revised presentation on a research project intended primarily to evaluate regenerative braking energy and CO2 emission differences between a 2-wheel dynamometer, a 4-wheel dynamometer and empirically determined rear-axle braking forces applied the same test conditions on a 2-wheel dynamometer. The expectation is that the two-wheel dyno tests will produce the highest regenerative braking energy and lowest CO2 emissions since it places 100% of the braking load on the rear axle.