Most of the results of OTA’s analyses of mid-size autos apply similarly, on a percentage basis, to other auto size classes—such as subcompacts—and to light trucks. There are, however, some interesting differences. For example, the aerodynamics of different vehicle classes are subject to different constraints.
Subcompacts are unlikely to attain as low a drag coefficient as mid-size vehicles because their short lengths inhibit optimum shapes for minimum drag. Pickup trucks, with their open rectangular bed and higher ride height have relatively poor drag coefficients, and four-wheel-drive pickups are even worse, because of their large tires and higher ground clearance.
And compact vans and utility vehicles have short noses, relatively high ground clearance, and box-type designs that restrict drag coefficients to relatively high values. Although each vehicle type can be made more aerodynamic, it is unlikely that light-truck drag values will decline quite so much as automobile drag values can.
Types of vehicles
Another important difference is market-based—historically, introduction of new technologies on light-duty trucks has typically lagged by five to seven years behind their introduction in cars. Although this lag time might change, it is likely that some lag will continue to persist.
Differences in the functions of the different vehicle classes will affect fuel economy potential, as well. For example, the load-carrying function of many light trucks demands high torque at low speed, and may demand trailer-towing capability. The latter requirement, in particular, will constrain the type of performance tradeoffs that might be very attractive for passenger cars using electric or hybrid-electric powertrains.
Whereas OTA expects the business-as-usual fleet of automobiles to improve in fuel economy by about 24 percent between 1995 and 2015, the fuel economy of the light truck fleet is expected to increase a bit less than 20 percent. Prices will scale with size: for example, for hybrids, subcompact prices will increase by about 80 percent of the mid-size car’s price increment, compact vans by about 110 percent, and standard pickups by about 140 percent, reflecting the different power requirements of the various vehicle classes.