If you love off-roading, there is no doubt that you would have come across some form of rock crawling or a rock crawler. Rock crawling, is the exercise of driving your vehicle, whether stock or modified, over the biggest, or steepest rocks and rocky terrain you can find. Whether for competition, or pleasure, a rock crawling vehicle, requires very specific equipment to be able to execute the task, and usually in general overlanding, you often come across rocky sections or terrain that you have to cross. So let’s take a look at what is important, and required on a rock crawling rig.
Slow and steady is the name of the game when it comes to crawling over rocky terrain, hence the ‘crawling’ in the name, and as such, your gearing is of utmost importance. In fact, often just upping the gear ratios, to provide for a lower first and second gear when low-range is engaged in the transfer case, is enough to already make your 4wd vehicle quite capable on the rocks.
The other, as important factor in rock crawling, is traction. So important, that without grip, you ain’t going nowhere. Traction is provided by the contact and grip of the tires, on the terrain. With a hard surface like rocks, the rubber compound of the tires need to be sticky in order to provide grip. The other major contributing factor of the traction and grip, is the size or surface area of the contact that the tires have with the terrain, so size matters.
So not only are larger tires important, but also extra thick sidewalls, as it is important to deflate the tires as much as possible, so they fold over rocks to grip them and also give so as to prevent sharp rocks from puncturing them.
In order to deflate the tires as much as possible, you need some form of beadlock, that holds the tire beads onto the wheels so they don’t fall off or separate. So the preferred wheel is a true beadlock which has has locking rings, that bolt onto the wheels and keep the beads fixed. Another option is either to use internal beadlocks on normal wheels, or to have someone custom fit locking rings to normal wheels.
The usual preferred choice for a rock crawling rig, is something with solid axles, as they often allow more articulation, strength and clearance at a lower cost. The axles will be taking quite a fair amount of abuse, so the stronger, the better, and although, generally stronger also means heavier, when it comes to a rock crawler, heavy axles are beneficial, as they mean more unsprung weight, under the suspension, lowering the vehicles center of gravity, and allowing for steeper angles without falling over.
Steering also proves to become a challenge with such large tires, having to be turned out of ruts, at slow speed without any momentum helping, so a stronger upgraded steering setup is required and helps. Either a hydraulic steering setup (which is illegal on road without a mechanical joint) or a hybrid hydro-assist steering setup, where it still maintain the mechanical steering linkage, with the added help of hydraulic pressure.
Although technology materials have improved considerably, allowing for stronger and more capable independent suspension axles, these are still very new, unusual and expensive to reasonably consider for the usual rock crawler.
Solid axles are connected to the frame by either a control arm suspension with coil springs or coilovers, a leaf-spring suspension setup or most preferred a link type suspension system offer some of the greatest articulation and versatility.
As much articulation as possible is the goal, as this helps keeps tires on the ground for traction purposes, but without lifting the vehicle which will raise it’s center of gravity and cause it to rollover more easily.
Independent suspension has improved by leaps and bounds the past few years, even in the rock crawling arena, however, the high costs of making an independent suspension system durable and tough, are somewhat prohibitive for anyone other than competitive rock crawlers.
The Center Of Gravity (COG) of your vehicle, is the average location of mass or weight of the vehicle. The higher up the center of gravity of your vehicle, the easier it tips over on steep angles, either sideways or incline and decline angles. This provides for a common problem in off-roading, which I like to call, the Lift Paradox.
The lift paradox occurs, when you want to increase the clearance under your vehicle, including the brake over, approach and departure angles, which is usually done by lifting the suspension or adding bigger tires. The larger tires also often requires a suspension lift to clear them or so they can clear the body panels. Now, although this all provides more clearance underneath prevent getting hung up on obstacles, it raises the center of gravity of the vehicle, bring down it’s tipping or rollover point. The one action contradicts the other in terms of off-road ability, so the contradicting wants for an off-roader, is a low center of gravity, with high clearance underneath.
When raising suspension, widening the track will help bring the COG lower again. For every inch of lift, we recommend adding two inches of width. Just remember that going too wide may prevent passing certain tighter trails.
Torque is the main factor to consider when it comes to a rock crawlers engine, as slow speed torque that pulls the weight of the vehicle over or up a big rock. This is the reason why either big-block V8 petrol engines, or diesel engines are preferred. However, the correct gearing in the transfer case and the axles can also compensate for smaller petrol engines.