If there's one thing we've learned, when you get the chance to drive a Tonka Toy, do it--and that's exactly what we did when the people at Unimog offered us a drive opportunity in a 2005 U500. Looking more like a behemoth reptilian insect with its flat face, tallish posture, and almost unbelievable strength and capability, the Unimog is the ultimate in heavy-duty gearing with command seating positions. Equipped with what essentially amounts to 40-inch tires and two 4x4 low-range ratios (one designated "working" gears; the other "crawler" gears), the Unimog can creep at 0.09 mph with a crawl ratio of over 3000:1. That means a crawling speed of 150 yards an hour--not idling; that's at a 2000 rpm engine speed (close to wide-open throttle for a diesel). But the Unimog's tremendous crawling abilities are only part of what makes this vehicle such a standout player on the road. Mixing both old-world and high-tech solutions in a single vehicle, the

Unimog has a long military history behind it, but is now used throughout the world for road maintenance, snowblowing, street sweeping, construction, and firefighting, and a few are even used as daily drivers. But at over $100,000 (before you add any of the thousands of options), it's no wonder Unimog only sells about 300 of the units per year to various municipalities and construction companies around the world, and fewer than 50 per year in the U.S.

The truck begins with a heavy-duty turbocharged, intercooled Mercedes-Benz 6.4-liter I-6 that puts out 700 pound-feet of torque, all of which sits directly underneath the three-seat cab. Without a hood to block the view, visibility is amazing, allowing for an easy line of sight in front of each tire. The heavy-duty transmission offers eight forward gears and six reverse, and uses a unique electronic-manual clutch that acts as a type of switch, allowing for quick gearshifts, as well as the ability to feather the clutch like a conventional spring-loaded unit. The act of selecting gears is done with a toggle switch on the gearshift lever, allowing up- or downshifts with a simple touch (even multiple gears), with all the readout information on the dash. If you do something it doesn't like (like going from first to fifth), a loud clicking sound lets you know you have to try again.

The U500's four-wheel drive is a permanent, full-time all-wheel-drive system with two separate gears for low range. Suffice it to say that the gear multiplication is spectacular and makes the crawling capability of this truck one of the best in the world. With working and crawler gears (the former identified with a donkey icon; the latter with a rabbit--we're not sure why), the amount of available torque to crawl over rocks and boulders is stunning, as we found out at a local off-highway vehicle park where we navigated a test course reserved for highly modified 4x4 buggies and custom trucks. Front and rear live axles have geared hubs (like the Hummer H1), and a central tire inflation system is available as an option, allowing the driver to both raise and lower tire pressures from the cab, with all psi information for each tire indicated on a dash display. We found the combination of big torque, big weight, and a huge footprint almost unstoppable when trying ridiculously steep hillclimbs. The only thing that prevented us from conquering the steepest motorcycle hill around was a large patch of soft dust that broke our traction from the front wheels and had us sliding toward a deep rut.