The deafening engines that send motocross bikes shooting off jumps and tearing up hillsides have earned the cycles a bad reputation. But a German entrepreneur wants to rehabilitate the sport -- with an all-but-silent new engine.

The Quantya is an electric motocross bike. Its silent motor might help redeem the sport's deafening bad-boy image. At first glance, the Quantya motocross bike doesn't leave a particularly tame impression. It looks like the usual cross-country motorbike, a vehicle for daredevils, the kind of riders who plow down muddy tracks and off high jumps with no regard for the natural world around them. And then, of course there's the noise: the motor's guttural RrrrraaaangtangtatatAAANG. Hardly any recreational sport has won so little acceptance in polite society.

Yet the Quantya is different. It can take on rough terrain just as well -- and no less destructively to the ground it covers-- as traditional motocross bikes, but with a difference. The Quantya does it silently, moving almost as noiselessly a bicycle. What's the secret? The bike's power source is electricity, not gas.