 However, in 2015, a paper in Journal of the Royal Society Interface claimed that "The drag-reduction performance of the two boxfish species studied was relatively low compared with more generalized body shapes of fish".Other parts of the design include the fact that the rear wheels are partially fitted with plastic and that it's considered as a lightweight vehicle.Mercedes-Benz reported a drag coefficient of 0.19; for comparison, the production vehicle with the lowest ever Cd value was the GM EV1, at 0.195.