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australia:offroad

going off-road / 4WD

Introduction

  • going off-road is very popular in Australia however it does require the right gear, preparation and technical training
  • buying “automatic” electronic features may allow you to get further off-road but unless you also have spent time learning the technical side of off-road driving, they are likely to just leave you getting stuck in more remote places!
  • If you hope to take full advantage of your vehicle’s angles, then you’re going to want to protect the bodywork. Off-road bumpers offer protection from bumps and scrapes while giving you the ability to mount accessories like winches, lights, and tire carriers. Rock sliders mount to the frame under your doors, protecting your vehicle’s body.
  • recovery gear such as a winch, shackles, a snatch strap, and recovery boards should be considered essential;
  • roof racks need to be a much higher rating if you plan to load them for off-road use
  • the cardinal rule for off-roading is never go alone - you will eventually get stuck and need help from another vehicle
  • it then also means having a two way radio to enable a spotter or a recovery vehicle to communicate with the driver is pretty much a necessity.

Determining factors in choice of vehicle

ruggedness and power

  • 4WDs with truck chassis are generally built more ruggedly and are better suited to most serious off-road work and towing but do need an engine with higher power specs and will have poorer fuel economy
  • roof rack rating is important off-road
  • the ability to get to and maintain momentum is important
    • momentum = mass x velocity
    • the ability to get to a given velocity is determined by:
      • power of vehicle to overcome the mass of the vehicle as acceleration = force / mass
      • force here is determined by the power from the engine less the effects of gravity (eg. going uphill against gravity)
        • high torque at low RPM is important for such off-road work
        • if you have a heavy vehicle then large tyres, twin lockers and a turbo V8 can get you up very slippery tracks where other vehicles may struggle
      • traction

capacity

  • shorter wheel base offers better angles but less passenger and cargo capacity
  • tare weight = weight of an empty standard vehicle with all of its fluids (oils, coolants) but with only 10 litres of fuel in the tank
  • kerb weight = same as Tare Mass, but with a full tank of fuel and without any accessories fitted (bull bars, tow bars, roof racks etc).
  • Gross Vehicle Mass (GVM) or Weight (GVW) = maximum your vehicle can weigh when fully loaded as specified by the manufacturer
  • Payload = maximum load (including accessories, passengers, etc) your vehicle can carry as specified by the manufacturer = GVW - Kerb weight
    • a Toyota Landcruiser 200 has a payload of only 600kg!
  • Gross Vehicle Axle Mass or Weight = maximum load that your vehicle's front and rear axles can carry as specified by the manufacturer
  • Gross Combination Mass (GCM) or Weight (GCW) = maximum weight allowed for your vehicle and trailer combined, as specified by the tow vehicle's manufacturer

adequate traction

  • inadequate traction is the cause of perhaps 90% of failures off-road
  • vehicle drive chain design can be critical to gaining traction
    • ability to lock both front and rear diffs
    • “AWD” vehicles generally are not able to lock both front and rear diffs and may send most of the engine's torque to the spinning wheel that has lost traction instead of sending it to the other wheel which has traction
  • the 1st upgrade you need to do is get a good set of all-terrain tires
  • appropriately adjusting tire pressure for the surface is critical
    • Lowering the air pressure of your tires increases traction because it allows more of your tire surface to grab onto whatever you're driving over and will also reduce risk of punctures
  • the heavier the vehicle, the greater the traction is needed

adequate clearance

  • a vehicle with very short front and rear overhangs will inherently have superior approach and departure angles to one with longer overhangs
  • a short wheelbase, will inherently achieve a better breakover angle than a vehicle with a longer wheelbase
  • lifting a vehicle up to gain improved clearance or angles by increasing the size of the tire will increase the height of obstacles it can roll over, but will reduce your effective gear ratio while adding unsprung weight which generally will just result in a poorer ride, worse handling, poorer braking, higher centre of gravity and rollover risk, and worse fuel economy without much benefit.
    • If you fit larger tires, you will need to change your differential gears in order to return performance, fuel economy, and control and you’ll need to fit taller suspension in order to clear them.
  • parameters to consider:
    • ground clearance
      • perhaps the least important of these parameters as you can usually drive your wheel over the highest point, but it still may be a factor
      • AWDs can sometimes have higher ground clearance than 4WD trucks with solid axles
      • clearance is important when driving through deep wheel ruts and it is here that the centre diffs of 4WDs may be the limiting factor
    • approach angle
      • the angle between your front tires and the lowest point on your vehicle in front of them
    • breakover angle or rampover angle
      • the angle from the bottom of either your front or rear tires to where the opposite tire meets the lowest point on your vehicle
      • this is related to the wheelbase - the shorter the wheelbase the better the angle
      • If you don't understand the break-over angle of your car, you can wind up balancing on a rock with all your wheels off the ground.
    • departure angle
      • the angle from the bottom of your rear tire to the lowest point behind it

low gear for steep obstacles

  • the ability to switch to a very low gearing is critical in delivering control to safely ascend and descend steep tracks

articulation

  • this is the ability for one wheel to be at a much different height distance from the vehicle body compared to the other wheel when one wheel is at a different height ground
  • in reality, this is only important for extreme 4WDers as most 4WDs usage can be performed if the driver is careful and controlled in their approaches.

ease of repairs while on the tracks

  • this also requires spare parts to be carried, tools, jacks, and knowledge of how to detect damage and repair it
  • a CV joint cage is likely to be damaged due to the shock loading when a spinning wheel lifts off the ground and then lands hard (eg. bouncing or hopping up a rocky incline) as this puts massive amounts of pressure on the driveline, and CV joints are usually the weakest link.
  • The CV joint (Constant Velocity joint) is more vulnerable:
    • if the car has been lifted as the angle is greater
    • on full steering lock under power
    • wheels are spinning for more than 3 seconds and not moving forward
  • the boot of the CV joint may also get punctured by a stick which allows the grease to escape and the CV joint will run dry and self-destruct
  • fortunately the CV joint can generally be replaced on the track with the right know-how and tools (and a spare!)

extras you may need to buy

is it a purpose built off-road only vehicle or a work vehicle as well?

  • you need to decide if you need the rear for your work or whether you can afford to always have that vehicle kitted out for off-road use and camping
  • try to keep it simple and avoid over purchasing accessories which will only empty your pocket and weight your car down and cost you in fuel
    • do you really need all that cooking ware?
    • are you really going to go to extreme tracks or just going on easy gravel tracks camping?
      • maybe you don't need mud tyres, bull bars, winches, roof racks, suspension mods, etc

tyres and suspension upgrades

  • all-terrain tyres (although mud tyres are fine on sand)
  • improved suspension to manage the weight of bull bar, winches, etc
    • balancing weight distribution from front to back and left to right is an important consideration

tools and repair kits

  • air pump for tyres
  • spare tyre
  • general repair tools
  • if you are going to extreme tracks or remote places then:
    • engine oil
    • diff oil
    • transmission oil
    • coolant
    • brake fluid
    • spare parts such as fan belts, CV joint or whatever the weakness is for your vehicle

towing gear

  • brake system such as Redarc electronic control

vehicle protection if going to extreme tracks

  • Off-road bumpers
  • Rock sliders mount to the frame under your doors, protecting your vehicle’s body.

river crossing options

  • air intake snorkel

auxiliary battery system

recovery gear

  • winch eg Runva
  • winch ring to allow a double line pull when you are really stuck in a mud hole but you might need the help of a 3rd line from a recovery vehicle's winch
  • shackles
  • a snatch strap
  • tree trunk protector
  • strap dampers
  • recovery boards
  • shovel
  • ?chain saw for fallen trees on tracks

camping gear

  • car fridge
  • cooking
  • awning eg. ARB
  • swag or roof tent
  • off-road rated roof rack
  • camp fire gear
  • chairs
  • drinking water
  • etc

technical aspects

load balancing your vehicle

  • most vehicles have a payload of 500-1000kg including driver, passenger, accessories
  • it it important to balance the weight distribution on each axle
  • keep heavy gear as low as possible to lower centre of gravity
  • roof racks need to be managed with care to avoid exceeding weight limits for off-road use
  • consider permanent heavy gear such as auxiliary battery and fridge in the rear passenger side to counterbalance the weight of the driver
  • if possible place spare tyres and extra water between the axles rather than to the rear to reduce risk of front wheels lifting up in ascents

highways

  • on dry highways, ensure you are not in 4WD mode (and particularly with locked diffs!) as this will create stress on your drive chain and bind it up
    • if you accidentally find you have forgotten to disengage 4WD mode, then slow down and drive for a bit with at least one side of the car on softer roadside to release some of the bound up state, then disengage 4WD mode
  • ensure your tires are pumped up again to highway pressures

gravel roads

  • lower tire psi a little (perhaps 30-35psi) to give more control and a nicer ride over corrugations
  • travel at the best speed for the conditions and no more than 80kph
    • going faster may cause damage due to vibrations causing screws to fall out or stress to vehicle not to mention risk of accidents at unexpected curves or animals
  • use AWD or 4WD (and lock your wheel hubs) to give the safest drive especially around bends where rollovers are a high risk if only in 2WD

green laning

  • relatively low risk driving on off-road tracks but may risk damaging the environment or the tracks if they are used mainly for horse riding
  • approach ditches or obstacles to cross at an angle not front on to avoid more than one tire losing traction at a time

rock crawling

  • driving slowly (less than 5kph) over rocky usually mountainous tracks
  • lower your psi to give more traction, better control and less bouncing which is likely to cause loss of control, rollovers or damage to CV joints
  • pick your line and plan your path out
  • consider using a spotter on difficult areas
  • sidewalls of your tires are the weakest part, so you need to be careful where they come into contact with rocks to avoid puncturing them
  • when ruts are dry, it's usually best to stay out of them and to straddle them instead and wider tires help give more purchase
  • avoid straddling large rocks because there's always a chance they could damage the underside of your vehicle - the best option is usually to drive over the rock with your tire or you may need to build a ramp of some sort on each side to get you over it and the departure angle managed
  • if you're moving too fast:
    • the side-to-side rocking motion of your car as the tires move over rocks can build up and cause your vehicle to tip, particularly if it has a high centre of gravity
    • you won't have time to assess the size of obstacles and your angles
  • if you plan on doing more extreme tracks, you will run the risk of damage to CV joints, axles, panels and more, so using your 4WDs as toys could be a costly venture

mudding

  • driving through deep mud is tricky as:
    • there may be hidden objects
    • each type of mud consistency requires different approach speeds for a given vehicle
    • going too slow will end up with you being stuck and trying to gain traction may just result in spinning the wheels and making a deeper hole and thus you almost certainly need to be winched or towed out
    • going too fast will risk losing ability to negotiate objects and maintain control
    • specially designed mud terrain tires are the best, these have extra large lugs which keeps mud from getting stuck in between the lugs, allowing you to maintain traction
  • driving up very slippery clay tracks
    • big mud tyres with aggressive side wall grooves and at low air pressure help
    • twin diff lockers can be really useful
    • adequate speed for momentum

sand dunes and beaches

  • dropping tire psi increases the length of tire in contact with sand and improves forward traction and this outweighs the effect of widening the tire
  • wider tires may actually be worse in sand as they create more resistance as sand is pushed in front but in reality wide mud tires will work just find if they are deflated to around 14psi
  • knowing your off-roading angles is important
  • like any hill, you have to gain enough momentum to reach the top without stopping
    • if you start too slow, you'll have to either back down the dune or make a wide arc to turn around
    • turning around on any hill is extremely dangerous because you're at greater risk of rolling your car over and ending up upside down.
  • the wider the tire (eg. as on dune buggies), the less you will sink into whatever you're driving through - lower your tire pressures for sand driving
  • heavier vehicles especially towing vans are more likely to get stuck in soft sand and an option for recovery is for another vehicle to use a snatch strap which will allow the towing vehicle to get some speed up without itself getting bogged

river crossings

  • these are potentially very dangerous
    • vehicles can easily get swept down the river
    • the lighter the vehicle, the shallower the water needs to be to float the vehicle and sweep it down the river
    • this is further compounded if the river if infested with crocodiles as they often are in the tropics of Australia
    • hidden obstacles or deep holes are a major risk
  • where possible, walk the path first and assess current, depth, obstacles, presence of deep holes, exit route accessibility and a recovery strategy in case of failure
  • crossing rivers you need to be ready with a recovery strategy such as a snatch strap to apply as soon as possible as getting stuck in a river with soft sand will rapidly result in the water eroding around the wheels and digging the wheels in deeper
  • salt water crossings:
    • cross at low tide which may differ to the beach low tide
    • drive slowly to minimise water splash which will risk corrosion
    • when home, thoroughly wash under carriage with fresh water

example vehicles

vehicle power torque kerb mass max. payload approach departure breakover clearance turn circle
Subaru Outback 6cyl 3.6L petrol 2016 191kW @6000rpm 350Nm @4400rpm 1626kg 430kg 18.5deg 22.7deg 20deg 213mm 11m
Ford Ranger 4×4 XLT Double Cab PickUp 5cyl 3.2L diesel 20211) 147kW @3000rpm 500Nm @1750-2000rpm 2135kg 1065kg 29deg 21deg 25deg 237mm 12.7m
Isuzu D-Max 4×4 3L 4cyl turbo diesel2) 140kW @3600 rpm 450Nm @1600→2600rpm 2030kg 1070kg 30deg 24-28.9deg 23.9deg 235mm 12.5m
Toyota Prado 2.8L Turbo diesel3) 150kW @3400rpm 500Nm @1600-2800rpm 2285kg 700kg 30.4deg 23.5deg 21.1deg 219mm 11.6m
Toyota Landcruiser 4.5L Twin Turbo V8 diesel 200kW @3600rpm 650Nm @1600-2600rpm 2740kg 600kg 32deg 24deg 230mm 11.8m
australia/offroad.txt · Last modified: 2021/05/05 22:40 by gary1