A common challenge to the packaging advantages of in-wheel motors is the trade-off required by moving the drivetrain mass from the sprung to unsprung. A commonly cited rule of thumb suggests that an increase in the unsprung mass/sprung mass ratio would result in vehicles with poorer ride quality. Protean's Andrew Vallance says that perceived problems with unsprung mass are blown out of proportion. He says research by Lotus Engineering suggests that top-of-the-segment performance can be achieved with simple techniques, such as changes to bushings and top mounts. "The Lotus work used objective, subjective and numerical analyses to investigate the effects of increased unsprung mass on a vehicle," he says.
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