[Diesel_Dave]

Ok, now I understand what you're saying. There may be something to that. Turbodiesels tend to have much higher low-end torque than gassers. Therefore they can be geared so that you can pull a heavy load with low speed and high torque, rather than having to run the rpms up. Therefore the diesel can be more efficienct than a gasser under heavy load, but the rolling resistance is the same.