Four Wheel Driving
By Michael Ecord

Driving off-road can be fun and exciting.  Avoid unnecessary problems by familiarizing yourself with your vehicle and the characteristics / personality of the machine.  It is important to know the capabilities and limitations of the 4x4.  Vehicle clearance, along with traction and depth limitations effect where and how a trail will be traversed.

 

Vehicle Clearance; Become familiar with the low points on your vehicle and their location in relation to tire position.  Common low points are differentials, spring & shock mounts, lower control arms, steps, exhaust, & spare tires.

 

Traction: Both the tires and the 4 wheel drive system effect traction.  Tire type and air pressure directly relate to traction.  Generally, the more rubber in contact with the trail, the better the traction.  This will be discussed further under trail types.  Many of the stock four wheel drive systems have limited slip or open differentials.  This does not allow equal transfer of power to all four tires.  Typically the right rear and left front tire are powered.

 

Depth Limitations: At some point you will be in a position to make a water crossing.  It is important to know the height of the air intake for the engine.  Also, the differentials, transmission, and transfer case have breather ports to allow the transfer of air during rapid heating and cooling of the unit.  Often there is rubber tubing extending the height of the breathers.  The height of the gas tank fill and vent tube is another location to remember. 

 

Driving Techniques

Terrain directly effects driving technique.  Hard ground, sand, and mud all require different styles. Be aware of what is in front of you.  If there is a blind spot or a difficult section on the trail, stop, get out and check it out before proceeding. Plan the route (line), taking care to remember about the low points on the vehicle.  Use a spotter to help guide through the difficult spots.  Also, it is important to remember which tires are powered and try to keep those on the ground.  On vehicles with solid (live) front axles, disconnecting the front sway bar can help by increasing the vehicles front-end articulation. Another way to increase traction on most dry terrains is to air down.  Airing down is the act of decreasing tire pressure to increase the footprint size of the tire.  A typical rule of thumb is not remove more pressure then necessary to deflate the tire enough to reduce sidewall height by 25%.  This usually means a tire pressure around 10-15 psi. Do not decrease pressure below 8 psi. Except in extreme cases.  It takes at least 6 psi. to mount a tire on the rim.    

When traveling in groups there are several additional items to remember. Look out for your fellow four-wheelers.  Do not follow to close. Allow the vehicle in front to clear an obstacle before proceeding, e.g. give enough room for the vehicle to back down the hill to try again.  Never loose sight of the vehicle behind, they may need to be spotted through a difficult section or aided in recovery.  

Rocky terrain: Ground clearance is very important.  Low gears, 1st-3rd are usually preferred. In dry conditions all terrain tires work very good, placing more tread on the ground then the same sized, more aggressive, mud terrains.  Large obstacles like steps and ledges can be approached from an angle, allowing one wheel at a time to mount the obstacle. Brakes should be used as seldom as possible and then only lightly.  Appling the brakes hard cause the suspension to compress, reducing clearance.  The slower the vehicle crawls over the rocks equals more control that can be maintained and less risk of damage.

Sand; Don’t do anything suddenly.   Try to stay in existing tracks.  Make wide turns and start and stop slowly. This is done to keep from building a wake of sand in front of the tires. It definitely helps to air down for driving in the sand.  All terrain tires will tend to rise on top of the sand while mud terrains will like to dig in. If the vehicle becomes bogged down, try to back out on your own tracks rather then punching the accelerator.  The later has the tendency to dig you in DEEP.

Hills should always be approached head on.  Never attempt to drive sideways on a slope.  This applies when ascending or descending.  There is a much greater risk to rolling the vehicle on a sideways approach as compared to the head on approach.

Ascents: Each ascent is different.  Gearing should be selected based on the severity of the slope. If the ascent is steep, climb the hill in low range. On a hard surface with ample traction, 1st gear in 4WL should supply all the torque necessary to clear the ascent.  If the surface is soft or there is a lot of loose gravel, 2nd or 3rd gear in the low range may be preferred to keep momentum up through the climb.  Caution, to much momentum can cause loss of control or damage to the vehicle.  Never attempt to turn around on an incline, let the vehicle roll back down the hill and start again.

Descents: Steep descents should be taken in 1st gear 4WL. Use the engine compression as a brake to slow the vehicle’s downhill progression. It is better to be in to low of a gear then to have an out of control vehicle (run away).  To reduce the chance of sliding, resist the temptation to apply the brakes hard on the descent.  If it is necessary to brake to keep the vehicle from running away, feather the brakes.  Vehicles with automatic transmissions will have to use their brakes as momentum increases. If the rear of the vehicle start to slide around on sandy or muddy slopes try to accelerate through the slide.  

Mud:  There are many different types of mud, from the bottomless slop to slimy clay.  Each type requires different technique and equipment.  What ever the type of mud, tires with large lugs are needed so the tire can clean itself.  Otherwise, the tires become slicks and most of the traction is lost. Aired down wide tires work best to float over the bottomless goo.  In mud that has a firm substrate, narrow tires that penetrate the mud offer the best traction.  Rocking the steering wheel back and forth helps the front wheels find traction.  Mud can hide holes and obstacles that will swallow a vehicle or chew up a tire.  Driving in the mud is very unpredictable

Water Crossings:  Be aware of the vehicles depth limitation.  Scout the water crossing for hidden obstacles and water depth.  Proceed at a slow pace, 2nd gear in four wheel low.  If the water crossing is over bumper height, maintain enough speed to push a 2”-4” bow wake in front of the vehicle.  If traction is lost during the crossing, slow the vehicle down. Avoid using the clutch on a standard transmission to keep water from getting between the flywheel and clutch plate. If the vehicle stalls because of water entering in through the air intake, do not attempt to restart the motor until it can be verified that there is no water in the cylinders.   Also, place recovery gear in an easy to reach spot just in case it is needed.

Ravines / Cracks; When crossing a ravine it is quite common to have two tires without traction.   Try to pick a line that will drop the drivers side front tire into the area first.  This way pressure is maintained on the driver’s side front and passengers side rear tires, which are the power tires in stock vehicles. 

More to come later….