related linksMSN Autos - Autoshow/Geneva/2012
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Rinspeed seems very practical. If you'll only need the battery, leave the engine at home. If you're going farther, attach the engine. (More weight & more rolling resistance.)
One concern: Is the steering less responsive? 2 rear axles tend to keep the vehicle moving straight ahead. One pair of rear wheels could be made steerable, automatically adjust to however the front wheels are steered -- at added expense.