Basically all of this is true...... unless you have a diesel in which case having a larger wheel and tire (over all dimensions) will create a slight strain increase on the engine but will create a much lower operating RPM at a given speed and there for increase the over all fuel economy by a great deal in some cases... the reason I site Diesels directly is because they react alot more to a 300rpm difference then a gasoline motor in terms of fuel consumption.