There are other aspects of the car's design such as keeping the flow of air attached to the body far to the back of the car as possible to minimize pressure drag (the Bernoulli relationship). A design with less drag means higher efficiency and an increased maximum speed, given the same powertrain.
Other aspects of the car's design include maintaining airflow attachment to the body as far back as possible to minimize pressure drag (the Bernoulli principle). A streamlined design with less drag results in higher efficiency and a greater maximum speed, given the same powertrain.