We recently got the following query from reader Felipe about electric vehicles (EVs) and we thought the answer would be of interest to many readers who are considering purchasing or leasing one of the upcoming crop of plug-in vehicles:

Hi, do you have any info for EV performance in hill terrain (paved roads). I believe all MPG testing is done on flat roads, and where i live most of the roads are high slope streets, so an underpowered engine is less efficient than a big one.

Felipe's assumption about mileage testing on flat ground is essentially correct. The standard drive cycles used in various countries all simulate acceleration, braking and steady-state driving on a flat surface. It's also true that running a smaller engine at its upper limit can result in lower efficiency than using a larger engine working at the sweet spot of its operating range. Read on after the jump to learn about the effects on EVs.

Compared to internal combustion engines, electric motors do offer a number of advantages, but these come with some disadvantages. One big advantage: electric motors stay near peak efficiency over a broader range, so working it harder is somewhat less of an issue. However, basic physics still comes into play. Driving uphill still requires more energy than driving on a level road and will drain the battery faster, cutting the range. That's why the Chevrolet Volt has a mountain mode that starts the range extender when the battery is at about 45 percent rather than the usual 30 percent.

On the other hand, what goes up, must eventually come down and this is where electric vehicles have a huge advantage because a big chunk of the energy lost during climbing can be recovered through regenerative braking when descending. Of course, since some of the energy is lost to friction, aerodynamic drag and electrical resistance, the car can't recover all of the extra energy but the overall impact will likely be less than it would for an internal combustion vehicle.

Regardless of where you drive, real world EV range is going to vary from posted results anyway as a result of using the climate control, headlights or window defoggers. We won't know for sure until we get to spend some time with EVs in hilly or mountainous terrain what the real impact will be on range, but it will certainly be reduced. Anyone considering a battery electric vehicles in these areas should keep in mind the range limitations and how far they have to drive before signing on the dotted line.

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