Four Wheel Driving

4WD systems:

• the original 4WD system:
  • basically rear-wheel driven with the front wheels engaged by levers or switches
  • don't have centre diffs or fluid couplings, so cannot be driven on bitumen in 4WD without high risk of transmission damage
  • eg. most utes, Nissan Patrol, Holden Frontera & Jackaroo, Jeep Wrangler & Cherokee, Suzuki Vitara
• full-time 4WD:
  • front & rear axles drive all the time
  • because these have centre diffs, they can be driven in 4WD high range (low range also on Land Rovers) on high friction surfaces without transmission damage risk
  •  eg. Toyota wagons, Land Rovers, Range Rovers
• all wheel drive:
  • Subaru
• automatic or selectable 4WD systems:
  • various forms include automatic, torque proportioning, & selectable

4WD vehicle - basic off road requirements:

• adequate fuel tank (eg. 90L)
• ground clearance
• approach & depart angles
• sufficient wheel travel in the independent wheel suspension to keep all 4 wheels on the ground when traversing uneven ground =>?live wheels
• firm suspension to cope with loads and repeated bumps
• power to tow loads, etc
• torque at low engine speeds eg 2800-3000rpm
• high air intake if river crossing
• 12V access in rear for fridge, etc

4WD Accessories:

• lights:
  • most 4WD lights are inadequate for bush driving at night
  • consider replacing with after-market inserts to give better beam spread, whiter light & improved distance
  • don't fit brighter globes in moulded plastic headlight units as these will melt
  • consider auxiliary lights to replace the next to useless under-bumper fog lights, but may need to be wired to high-beam circuit
• bull bars:
  • ensure specs are adequate to protect from animal strike as many are just for show
  • ensure strong enough to mount winch, lights, aerials
• winch:
  • is a great insurance if you are travelling alone
  • power winch is a lot easier to use than a manual one
  • read manuals to avoid damage to driveline when driving on-road
  • if electric, may need additional battery capacity
• interior:
  • cargo barrier:
    • essential to prevent potentially lethal missiles if rear is packed
• fuel capacity:
  • only Toyota & Nissan make 4WD wagons with adequate fuel tank capacity
  • consider fitting a single larger tank rather than auxiliary pump as transfer pumps are unreliable
• suspension:
  • heavily loaded vehicles may impact on standard suspensions
  • bar work & winch up front may require heavier front springs
• tyres:
  • standard tyres on new 4WDs are usually inadequate for bush driving
  • in general, any tyres with 70-profile or 75-profile shape are too lightly built
• traction aids:
  •  all new 4WD wagons come with limited slip diffs (LSD's) or traction control as standard & for most people that is all they will need, (esp. if have Nissan Patrol or Prado diesel) however, serious off-roading you may need more (esp. if Toyota Land Rover):
    • stronger LSD
    • self-locking rear diffs (eg. Detroit NoSpin)
    • driver-controlled diff locks (eg. ARB's Air Locker)
• towing:
  • automatic transmissions may need an oil cooler fitted to prevent over-heating
•  

4W Driving:

• ensure you have appropriate topological maps +/- GPS
• travel at appropriate speed for terrain:
  • too fast will cause:
    • shock absorbers to over heat if driving over corrugations
    • upset the passengers
    • miss seeing and thus avoiding obstacles or pot holes
  • you cannot memorise in 3D every obstacle in a path so if unsure have someone guide you past them
• steep grades:
  • in general travel down the grade in same gear it required to get up it
    • ideally use engine-braking to retard speed downhill, but this is only possible on heavy-duty 4WDs that have deep-reduction gearing, most wagons, particularly automatics, lack sufficient engine braking
    • if you keep momentum low & the track isn't too slippery, light braking won't cause wheel-lock, if it does, get off the brakes quickly, then reapply lightly again
    • if you have ABS, the brake application needs to be heavier to make ABS work properly on all four wheels
  • if front wheels cannot be locked at same speed as rear wheels in low range then this can result in vehicle moving sideways!
  • make sure you do not end up sideways esp. when going downhill as this risks rolling over
• beaches:
  • you are more likely to kill or be killed driving on beaches than any other off-road surface
    • roll over
    • head on collision or running over people due to poor visibility (sun on sand creates disorientation) or distractions
  • the best sand vehicles are light
  • wet sand near the waveline may be hard but an odd soft patch can send you off-course without warning into the sea
  • know your tides, never drive along waveline on a rising tide
  • sand tyre pressures:
    • tyres deflated to half normal pressure are safe at only 40kph or so & even then won't respond to braking or steering as accurately
    • doing spectacular sand-splitting donuts as seen on TV ads risks blowout or tyre coming off the rim
    • finding the correct pressure is largely trial & error for a particular vehicle with a particular load, but most put lower limit at 16psi
    • never drive on roads at these pressures!
  • sand bogs:
    • tow using a web snatch - an elastic webbing robe that whips the car out of the bog
      • shovel out smooth ramps in front of each tyre first
    • if alone, then need to "roadbuild" with the vehicle jack using rocks, timber, shrubbery or sand and a winch is very helpful here
• rivers:
  • always wade through the river first if you cannot clearly see the bottom as obstacles such as logs/rocks or deep potholes may cause problems
  • only attempt wading across if:
    • max. depth in metres x speed of current in m/sec is < 1, else you risk floating or drowning down the river
    • no crocodiles, etc
  • in general, cars should avoid water deeper than half the height of its wheels if you value your car!
  • engine requires constant flow of air to keep running:
    • ensure air intake is high enough
    • avoid stopping car as this risks stalling
  • ensure air conditioner is turned off so that radiator fan stops to prevent it getting distorted in water and damaging the radiator
  • if stalled in middle of deep river or caught in a rising tide at beach, first priority is getting everyone to safety!!

Assessing used 4WD's:

• this is notoriously difficult and probably should be avoided unless it is clear it has not been used off-road much, but some things to check for include:
  • determine what sought of life the vehicle has had:
    • front differential housing & underbody splash tray:
      • scratches & gouges show that it has done some off-road work
    • lubricant condition in front & rear diffs - any milkiness suggests water has entered housing, probably through a combination of a blown axle seal & the odd river crossing
    • noisy drivelines
    • shock absorbers:
      • an oil mist on them indicates blown seals
      • blistered or bubbling paint indicates shock has been very hot at some stage such as fast driving over outback corrugations which causes the shock's oil to break down & not work as well as it should
    • if suspension upgrade:
      • vehicle more likely to have been driven in rough conditions
      • firmer suspension also places greater loads on the mounting points & may result in fatigue-cracking, thus carefully check for metal cracks where the cabin is bolted onto the chassis.
    • if body is rubber-mounted to chassis (eg. Range Rovers), any looseness will cause the vehicle to feel sloppy
    • centre diff is critical to the driveline:
      • scalloping on outer edges of tyres as they tear themselves to bits on the road due to faulty (esp. Land Rover Freelanders)
    • any plates welded onto chassis rails are probably rust repairs or gussets added due to chassis cracking
    • service record
      • diesel engines:
        • must not skip oil changes
        • injectors need servicing every 100,000km or so

4WDs in Australia:

• truck-chassis 4WD "tanks":
  • tend to have 4-5L engines either V6 or V8, thus very poor fuel economy ~20L/100km
  • avg price $55000-70000 2001
  • Toyota LandCruiser:
    • 1st imported in 1957 to transport construction workers on the Snowy Mtn Scheme
  • Nissan Patrol
  • luxury vehicles ($85000-$120,000 2001):
    • Range Rover
    • Mercedes M-class
  • whilst still in the top 10 4WD best sellers in 2001, are a dwindling 22% market share of 4WDs
• mid-size 4WD wagons:
  • 6 cylinder 4WD as a good compromise between off-road & on-road driveability, but heavy on fuel consumption
  • by 2001, have 45% of 4WD market share with average price ~$50000-$60000
  • Jeep Cherokee - best blend of performance, handling, interior & off-road capabilities
  • Mitsubishi Pajero - almost as good as Jeep; 7 seats;
  • Nissan Pathfinder - slow, poor ground clearance, not roomy, old design but good build quality
  • LandRover Discovery - reliance on electronic traction & hill descent control impairs off-road
• light "cross-over" 4WD wagons:
  • good on-road driveability with good fuel consumption, but still capable off-road although lack low-range gears
  • 4 cyl or small (3-3.5L) V6
  • average price $35000-45000 2001
  • Subaru's Forester (1997) - low range gears
  • Mazda Tribute & Ford Escape (2001) - centre diff lock;
  • Nissan's X-Trail (2001) - excellent on-road; very roomy; new interior styling
  • luxury vehicles:
    • BMW X5 ($82,000)
• compact 4WD wagons:
  • generally 4 cylinder vehicles, mainly for on-road driving, with limited off-road capabilities
  • Suzuki Vitara launched in 1988, was an early sign of things to come, with an avalanche of models appearing by the late 1990's, primarily used for city driving, stimulated by the launch of Toyota's fuel efficient RAV4 in 1994, but accelerated in sales in 1997
  • Honda's CRV (1997) - front-wheel drive which kicks in rear wheel drive when senses wheels lost traction. Poor off-road;
  • by 2001, had gained a steady 33% market share in 4WD market
• all-wheel drive station wagons:
  • mainly for on-road driving, with limited off-road capabilities
  • Subaru Liberty launched in mid-1980's
  • Subaru Outback launched in 1996, transformed the soft-roader formula, setting the standard for "crossover" vehicles
  • luxury:
    • Subaru Outback H6
    • Volvo Cross Country