Besides shape, weight is one of the prime obstacles to good fuel economy. It takes more power – and, hence, more fuel – to start up a heavy vehicle than a light one and to keep it at speed. Perhaps you’ve noticed the difference in mileage between driving an empty car and one loaded with passengers and cargo. Even the difference of 100 pounds can affect fuel economy.
As a result, manufacturers focus on weight reduction with each succeeding model, despite a corresponding increase in vehicle content (i.e., added and evolved safety systems, audio systems, comfort and convenience equipment).
In order to maintain low curb weights and reduce them wherever possible, Subaru uses technologies in its vehicle bodies and mechanical features that allow lower weight with increased strength. Greater proportions of high tensile strength steel are employed in all Subaru bodies, and strong, lightweight metals are used in components throughout the model lineup.
In addition, lightweight unit-body structures are the foundation for Impreza, Legacy, Outback, and Forester models. These same models have window glass of reduced thickness.
Measures taken under the hood reduce weight, too. All Subaru engines have aluminum-alloy blocks and cylinder heads and all Subaru transmissions have aluminum-alloy cases. Not only does this construction reduce overall weight, it helps to improve the front/rear balance of the vehicle for improved handling. The engines’ pistons have a lightweight design, and the intake manifolds are made of resin, which also contributes to weight reduction.
The 2012 Impreza pushes the envelope farther with optimized lightweight aluminum-alloy wheels and aluminum-alloy rear brake calipers.
Notice that we’ve only lightly touched upon engines and transmissions. We’ll have more to say about them in the Winter 2012 issue, in which we’ll present additional ways in which Subaru vehicles are built to achieve good fuel economy. In Part Two, we’ll look at vehicle design and how components and systems are engineered to function efficiently.