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"  1. Mild Buildup   Vehicle: Newer 4WDs like the Nissan Xterra have a smooth-riding independent front suspension. They can tackle easy trails with minimal modifications and still maintain on-pavement road manners. Engine: Don&amp;#039;t void the warranty. Reusable air filters improve filtration and breathing. When combined with an exhaust system that installs behind the catalytic converter, these safe upgrades can yield up to 10 hp. Suspension: Maintain stock height to preserve the factory handling and stability. Aftermarket off-road shocks can offer better control over rough terrain. The tradeoff? A firmer ride on the street. Tires/Differentials: Large tires hurt fuel economy and off-the-line thrust. Instead, mount a stock-size mud tire. Choose a limited-slip differential for the rear axle to get better grip on pavement and off.  Protection/Recovery: Aluminum skidplates underneath help protect drivetrain components. A tow hook or clevis shackle bolted securely to the frame is essential for snatch-strap or winch recovery. The Right Stuff: Goodyear&amp;#039;s aggressive new Wrangler MT/R mud tire has a Kevlar sidewall to reduce punctures and a rim protector to guard against wheel damage in all terrain. The MT/R comes in 30 sizes.  2. Moderate Buildup   Vehicle: Trucks with a live-axle front suspension, like 1973-1991 Chevy Suburbans or comparable K-Series pickups, make tough platforms. These vehicles can be bought and built inexpensively.  Engine: Worn-out V8? Swap in a factory crate motor for reliability and increased power. Powerful motors can break parts. So plan to upgrade the drivetrain if you add serious horsepower. Suspension: A modest 2- to 4-inch taller suspension system and longer shocks create room for larger tires, increase axle articulation and boost capability. But systems with more lift typically ride rougher. Tires/Differentials: Taller and wider 33- to 35-inch tires raise ground clearance over obstacles and improve flotation. Add a selectable locking differential in the rear axle for maximum traction at both rear wheels. Protection/Recovery: A winch can extricate your truck from the worst-case-scenario stuck. Electric winches are expensive but worthy investments--especially when four-wheelers travel alone.  The Right Stuff: Warn&amp;#039;s PowerPlant Dual Force HP is two tools in one: a 9500-pound, single-line pull winch and an air compressor to inflate tires on the trail or run impact tools. Auxiliary air tanks are available.  3. Extreme Buildup   Vehicle: A classic two-door Jeep CJ or Wrangler is a perfect blank canvas to build a hardcore 4x4. Jeep parts are plentiful, and there&amp;#039;s a deep knowledge base for what works--and what doesn&amp;#039;t.  Engine: A V8 or diesel conversion delivers the torque to turn large tires. Upgrade to larger heavy-duty-truck-spec axles, transmissions and transfer cases, which are often needed to handle the stress. Suspension: Expensive coil-link systems can provide incredible suspension flex for serious rock crawling. They offer excellent ride quality on the road too. Tires/Differentials: To clear boulders, opt for tires size 37 inches and up. Suspension articulation helps maintain traction. But the toughest trails require a locking differential--in both axles--for true 4WD. Protection/Recovery: Minimal bodywork means less potential damage on the trail. If the Jeep has no hardtop, consider a full roll cage to protect in case of rollover. A winch is de rigueur in this class of vehicle.  The Right Stuff: Coilover shocks like Bilstein&amp;#039;s 9100 provide the potential for long wheel travel. The shock valving can be specified for any terrain--from slow rock crawling to high-speed desert runs. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/cars/motorcycles/a4273/4317334/>