Ground Clearance. If you intend driving on deeply rutted tracks then the first thing you will need is more ground clearance. There are 3 ways of doing this.
- Suspension Lift. This lifts the body and the chassis of your vehicle. If you have a solid axle (also called a “live axle” i.e. not independent suspension) the height of the axle and diff will not change. A suspension lift is the minimum recommendation for difficult rated trips. In Victoria you are legally allowed a 50 mm suspension lift. (see Legalities below).
- Larger Tyres. are the only way to get solid axle diffs and bottom shock absorber mounts, higher off the ground. Check your vehicle Speedo against a GPS Speedo. It is not uncommon to find your Speedo is more accurate after fitting larger tyres. In Victoria, 25 mm increase in tyre radius (50 mm in diameter) is legal. (See also Rim Sizes below).
- Body Lift. This is normally only fitted to vehicles that don’t need to meet legal requirements as a suspension lift is more effective and will lift the vehicle to the legal limit. A body lift involves fitting a spacer between the chassis and the body which only lifts the body. It does not lift the chassis.
Suspension Lift vs Larger Tyres. (If you are only going to do one or the other.)
While larger tyres are the only way to lift your diff higher off the ground, you are limited to 25 mm and the same clearance can often be achieved by good wheel placement over obstacles. Larger tyres may also affect your fuel consumption. A suspension lift gives you 50 mm of extra clearance which is more likely to reduce panel damage. For difficult rated tracks the best solution is to do both which gives you 75 mm of extra clearance which is more likely to have an effect.
Legalities. In Victoria you are legally allowed to lift your vehicle 75 mm. This can be made up of no more than a 50 mm suspension lift plus 25 mm on the tyre radius. Unfortunately, these laws are not universal throughout Australia and while Queensland has come into line with New South Wales and Victoria, you should check the current situation of other states before travelling over the border.
Disadvantages of Lifting Your Vehicle. Check whether your vehicle will still fit in your garage, especially if you’re planning to fit a roof rack at a later stage. Lifting a vehicle will raise the centre of gravity, making the vehicle slightly less stable. Larger tyres will increase the unsprung mass which will affect the ride and fuel consumption – being heavier it is also harder to do a wheel change and the larger diameter tyre may not fit in your spare wheel carrier. If you are driving hard rated tracks then generally the disadvantages are outweighed by the advantages. Many of the disadvantages can also be overcome by adapting your driving style (this is not a sports car), better shock absorbers and the way you pack your 4WD.
Tyres. Tyres used on 4WDs should have a Light Truck rating with LT as part of the tyre specification code. These have a stronger side wall and are less prone to being damaged.
There are 3 basic types of tyre:
- Highway Tyres. These are fine for sand driving or on easy tracks only if it is dry but are not suitable for any other off-road driving.
- All-Terrain Tyres. A good all-round tyre suitable for off-road and highway driving.
- Mud Terrain Tyres. While their chunky tread can give more grip in mud and on rocks, generally there is no need for these tyres, which on the highway can be noisy and wear out more quickly. Surprisingly, they work fine in sand although you may need to let out more air than you would with an AT.
If any of the above tyres are not performing well in any off-road situation then let out more air. As the tyre tread wears out you may also find that you need to run lower pressures off-road.
Since we are discussing fitting larger tyres, we should also discuss rim size and material before you buy new tyres.
Rim Sizes. Modern styling suggests that 19 inch rims are better than 16 inch rims but in four-wheel driving this is not the case. We are looking for as large a sidewall as possible to allow for more tyre flex and less likelihood of damaging the rim. There are other issues to consider such as comfort, road noise and wet and dry handling. Your choice of tyre type and brand will probably make more difference to these issues than will the choice of rim size. If your vehicle comes fitted with 18 inch rims or larger and a different badge series has 16 inch rims, check to see if those rims will clear your braking system. You can also buy aftermarket steel rims to suit most 4WDs
Rim Material – Steel or Aluminium. There are pros and cons for both and the most suitable will depend on your personal situation. Aluminium rims are lighter and will contribute to better fuel consumption and ride but if they are badly damaged against a rock, that is probably the end of them. If you are planning a lot of outback travelling then steel rims may be more suitable
Shock Absorbers. If you are planning long-distance travel on corrugated roads then be aware that standard shock absorbers can overheat and fail in these conditions. Consider fitting remote canister shock absorbers or even adjustable shock absorbers. These can be very expensive but a good set will transform the ride in your vehicle over rough roads and also on the highway.
Winch. If you are travelling on hard rated tracks, then needing to do a vehicle recovery becomes more likely. If you are travelling in a group there may be other solutions but there are times when a winch is the best answer. If travelling by yourself, especially in remote areas, then a winch becomes a necessity and could even be rated as safety equipment.
Bull Bar. If you fit a winch then you will also need to fit a ball bar (or a smaller version of a bull bar) in order to mount the winch. (Not all Bull Bars are designed to take a winch.) Bull Bars usually give you a better approach angle than the original bumper bar (which is usually removed) and are useful for mounting antennas and driving lights if you want to fit them.
Cross Axle Diffs Locks. Maximum traction is obtained when all 4 wheels are rotating smoothly. While Traction Control (TC) can make all 4 wheels rotate, it is a reactive system so the wheels have to be spinning first before TC will operate. Cross Axle Diff Locks give a constant drive to the 2 wheels on that axle and so are much more effective, especially in sand when driven gently. If you are only going to fit one locker, fit it to the rear axle even if you already have a Limited Slip Diff in that axle. A Diff Lock on the front axle is a helpful accessory but you will use it less often as it affects the steering to a point where the vehicle might not turn at all, even with the steering wheel fully rotated. An increasing number of 4WDs are being manufactured with a Rear Cross Axle Diff Lock as standard equipment.
Snorkel. A snorkel has 2 functions: 1) reduce the amount of dust going into your air filter, 2) reduce the possibility of water going into your engine during a river crossing. This last one is particularly important for diesel engines which are very high compression and will not tolerate the smallest amount of non-compressible water in the piston cylinder. Be aware that some snorkels are only rated as dust proof. Some air filter boxes are fitted with a one-way valve to let water flow out – others just have a drain hole. The problem with just a drain hole is that water can also come in. You will need to plug this hole before doing a water crossing.
Diff. Breathers. These are air pipes which allow the air pressure to equalize in your front and rear differentials and are also fitted to the gearbox. They stop water being sucked into the diffs and gearbox through the bearings when the hot or even warm steel is dipped into a cool river crossing and the air inside cools and contracts. Some 4WDs come with them fitted as standard equipment but if your vehicle doesn’t have them or they are not vented high up in the vehicle, you need to fit them before doing a deep river crossing.
UHF Radio. If you are traveling in a convoy (such as a 4WD Group trip) then you will need a UHF radio.