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Building Rock Crawling Off Road Trucks - RocK LogicSimple Rockcrawling Upgrades From the July, 2008 issue of 4Wheel & Off-Road By Fred Williams Photography by Fred Williams
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Rock Rule #1 Wear your s... Rock Rule #1 Wear your seatbelt. Mud can get sucked into engines and stop them dead while holding tight to your frame-rails. Sand can sneak by seals and churn away in your bearings, not to mention filling your carpet with millions of sharp granules. But rocks can ravage your undercarriage, destroy your rocker panels, wedge your tires tight until your U-joints self-destruct, hold you firm by either differential, and still tip you over or upside-down when you least expect it. The funny thing is all those challenges make rockcrawling so much fun. It's a challenge to pick the line with the fewest number of granite gremlins trying to grab an axle and impede your progress. Then there is the trick of knowing when to throttle or bump your way up an obstacle and when to drop it into granny low and let the gearing and traction pull you forward. Rockcrawling takes all types of skill, but building for the rocks doesn't need to be so challenging. Rockcrawling can seem intimidating to the rookie rock wheeler, but don't be scared and don't think you need to have the latest, craziest rock buggy to even attempt a boulder-strewn trail. In fact, four-wheelers were rockcrawling decades before the first rock buggy was ever built out of tube and coilover shocks. Of course every rockcrawling trail requires a different type of truck to truly dominate since wheelbase, power, gearing, and tire size can all come into play. That is what is so much fun about it. Every combination can have a good or bad day on the trail depending on how well the driver knows his vehicle and what it will do. However, there are some popular upgrades that make sense when hitting the boulders. Read on.  Even though a suspension that...  Even though a suspension that keeps all four tires on the ground is important, so is a set of locking differentials that keeps all four wheels turning. Automatic or selectable lockers both work great in the rocks, and when you're climbing a boulder and one wheel reaches for the sky, you'll be glad that locker is sending power to the wheel with traction to keep you bouldering forward.  One of the most important...  One of the most important upgrades to your rockcrawler isn't even an upgrade at all. It's a change in your state of mind. We're not talking booze, but rather your outlook on body damage. It's not easy, but when you realize that every scratch, dent, or mangled fender is a record of your rockcrawling trips, you'll be a more relaxed wheeler. A good set of rock sliders can keep you from getting hung up on thin body sheetmetal, but covering your whole rig in 1/8-inch plate would be excessive and heavy.  What's under the hood of your...  What's under the hood of your rock ride is important, but not in the way you might expect. A high-powered V-8 can be fun, but a reliable, reasonably powered, and torquey engine with an aspiration system that runs at extreme angles is way more useful in the rocks. Adding an engine cage to protect the engine should you go belly-side up isn't a bad idea if you are getting into more extreme wheeling, though many old Jeeps have been wheeling fine without one for decades.  For years the rockcrawling...  For years the rockcrawling trend was dead-set on having the most flexible suspension possible. Over time we've learned that you can go too far with articulation, but having a truck that can keep most, if not all, of its tires on the ground will help keep the truck moving. Every suspension design conceivable has been thrown at the rocks-from airbags to coil springs-but you would be amazed at how well a good old set of leaf springs will do. Keeping them long and flexy and mounting them above the axle helps articulation and ground clearance. On the other hand, going below the axle aids in controlling axlewrap from your low differential gears and grippy tires.  Even if you don't get into...  Even if you don't get into the insane cliff-climbing trails you should still have a solid rollcage in your 4x4. For optimum safety, we'd like to see the seats mounted to tubes that are tied in at the bottom of the rollcage. Then mount the cage through the body and down to the framerails because sometimes you flop over and sometimes you keep barrel rolling down the side of the hill. Make sure the tubing is at least 11/2 inches with 0.120-wall thickness for the lightest weight rigs, and thicker and larger as vehicle weight increases.  In the tire realm, the rule...  In the tire realm, the rule of thumb is big, aggressive, and sticky. But big tires require stronger steering with hydraulic ram assist or full hydraulic. Aggressive tires like mud terrains can be loud if your rockcrawler is also your daily driver, and sticky tires are usually only available for off-road rockcrawling competitors. We feel the longer the wheelbase, the larger the tire you want to run, as this helps on the break-over angle, which keeps the belly from hanging up. A short Jeep works great on 35s and a long fullsize would be happier on 39s or up to 47s.  Sometimes the best way to...  Sometimes the best way to build for the rocks is to get rid of anything that hangs you up and adds excessive weight. Stock bumpers reducing approach angle? Cut them off. Rear quarter-panels catching on rocks? Dig out the Sawzall. Doors inhibiting your visibility? Leave them at home.  Recovery gear should be handy...  Recovery gear should be handy when rockcrawling even though most of the time you just need a short little tug to climb up or off some rock. Winches are extremely handy since a snatch strap is hard to use if your buddy's truck can't get up the rocks to assist you. Many rockcrawlers have switched to the winch rope instead of cable since it is lighter.  When the boulders start reaching...  When the boulders start reaching up for your truck's vital drivetrain components, it's good to have some skidplates. We'd love to see everything sealed up tight like this Jeep/buggy where the skidplates are covered with UHMW (Ultra High Molecular Weight) Polyethylene, an abrasion-resistant thermoplastic polymer that has excellent sliding characteristics. But even a simple skidplate under the oil pan, transmission, and transfer case is better than nothing at all and allows easy access and heat dissipation.  Rather than sitting at home...  Rather than sitting at home worrying that your axleshafts aren't strong enough, why not go wheeling and see how they do? We like showing you super heat-treated chromoly axleshafts and U-joints made out of triple titanium alloy, and if you drive like a maniac and wedge giant tires into deep crevices with the throttle matted, then you probably need them. If you're just getting started, don't stress over it. Make sure your steering box is bolted tight to the frame before and after every wheeling trip, check all the tie-rod ends, and keep all the driveshaft bolts tight.  Transmissions will forever...  Transmissions will forever be a point of discussion amongst off-roaders. Some will swear by their manual trans with granny low First Gear, where others will choose the two-pedal automatic with ease of shifting to let you concentrate on the trail ahead. The fact is that both work great and choosing whichever is most comfortable for you is the best bet. Automatics are the most popular choice we see on the trails these days, but they need to have a good cooler since the torque converter will be working hard when crawling up large obstacles.  Axle differential housings...  Axle differential housings are the majority of the noisemakers and anchors on a rocky trail. The smaller Dana 44s and Toyota axles are appealing, as are aftermarket axles such as Dynatrac's ProRock housing, which is notched for maximum clearance. The legendary portal axles found under Unimog and Volvo off-road trucks are finding their way into many rockcrawlers with their amazing diff clearance, and newcomer Portal-Tek is coming to market with fresh new portals. We've seen every homebuilt method under the sun to gain a few extra inches of diff clearance such as this heavily modified 14-bolt housing.
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