It's hard to get a handle on how many people engage in off-road motoring, but the industry sells about a half-million vehicles each year that are designed to keep going when the pavement stopped.

For years, the market was dominated by ATVs, three and four-wheeled vehicles that could climb racks of boulders and dig through sand dunes.

The latest craze is a category known as UTVs, or more commonly, side-by-sides. These have two seats, a steering wheel, and room for quite a bit of gear. There sort of like cars, if your car could negotiate a bog full of mud and climb over a small mountain.

The latest UTV's are emphasizing performance, and raw speed. Earlier models, adapted from farm vehicles, topped out at school zone speeds. But the new side-bys can scream across the dirt at up to 80 mph.

Our Wheel Thing guru Susan Carpenter is a fan of going off road, and she tells us all about why so many people agree with her, and the latest ways to go really fast without any pavement.