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A Guide to Fitting Bigger Tyres on Your 4WD

A Guide to Fitting Bigger Tyres on Your 4WD

Monday, February 4, 2019

A Guide to Fitting Bigger Tyres on Your 4WD
One of the first things that many 4WD enthusiasts do after buying a new vehicle is install bigger tyres. There’s a couple of reasons why folks do this but the primary reason is to increase the vehicles ground clearance. There’s a common misconception that a lift kit will also increase your clearance, but they only lift the chassis and body of the vehicle. The only way to get better ground clearance is by installer bigger tyres, but 4WD owners need to be careful to ensure they remain within the legal modifications limit within their state.
As installing bigger tyres is such a hot topic, today we’ll be providing you with a guide to fitting bigger tyres on your 4WD.
Why bigger tyres?
The two primary reasons why 4WD enthusiasts fit bigger tyres is to increase the vehicles ground clearance and provide better traction through a greater surface area. Some 4WD owners also like the way the vehicle looks with bigger tyres, but that’s just personal preferences.

  • Increased ground clearance

It’s important to remember that installing bigger tyres only has a small increase in ground clearance. Tyres that are 50mm bigger in diameter will only increase your ground clearance by 25mm (or the increase in radius), which isn’t really much is it?

  • Better traction

The larger the tyre, the more surface area is in contact with the ground which provides better traction and flotation. 4WDs with bigger tyres perform better in sand and mud simply because more tyre is touching the surface and there’s less chance of getting bogged.
What about the type of vehicle?
The type of vehicle you buy is a big factor to how much ground clearance comes as factory. For example, if you compare a 1990’s Hilux with a 2010’s Hilux, the difference in ground clearance is significant. Older vehicles with solid axles have far greater ground clearance than newer vehicles, so the type of vehicle is a vital consideration if ground clearance is important to you.
What are the legal limits?
In Australia, each state has different laws relating to 4WD modifications which must be followed or you can face serious consequences. If you ignore the legal limits and install bigger tyres, you won’t just get a fine or a yellow sticker, you could possibly go to jail and be burdened with huge medical costs if you have an accident and your insurance company won’t cover you.
In Western Australia for example, you can increase the size of your tyres by a maximum of 50mm in diameter which only offers a 25mm increase in ground clearance. If you want to increase your ground clearance any further, the only way is to get engineers approval. If you’re interested in discovering the legal modifications limit in your state, simply click here.
What are the drawbacks to bigger tyres?
As with any 4WD modification, there are always drawbacks which must be considered. Installing larger tyres has several disadvantages which are outlined in the following:

  • Speedometer/odometer inaccuracy

Larger tyres will have a significant impact on your speedometer and odometer. If you increase the size of your tyres by 50mm, then you can expect your speedometer/odometer to be out by roughly 10% (which is the legal limit). This varies from vehicle to vehicle, but it’s something which should be noted.

  • Less torque and power

Larger tyres means that your RPM will be less but your engine needs to work harder. Again, each 4WD is different but expect to see a noticeable difference in torque and power which you can check via an EGT (Exhaust Gas Temperature) gauge.

  • Reduction in braking capacity

Arguably the biggest reason why there are legal limits to fitting bigger tyres is the reduction in braking capacity. Your braking capacity is reduced in proportion to the increase in tyre size, however if you stick to the legal limits then you should be fine.

  • Reduction in fuel economy

Since your engine needs to work harder to rotate larger tyres, you will see a reduction in fuel economy. When trying to work out your fuel consumption, make sure you factor the speedometer/odometer inaccuracy as well. Most vehicles can expect to use an extra litre or two per hundred kilometres.
What are the alternatives to bigger tyres?
At the end of the day, 4WD enthusiasts install bigger tyres because it makes their vehicle more capable. Despite this, there are other ways to do this such as installing lockers or changing your tread pattern. Lockers make most 4WDs far more capable and muddies offer considerably better traction than all terrain. When deciding what modifications to make, it’s vital that you consider your individual requirements such as the type of terrain you drive and how often you off-road.
While installing bigger tyres increases ground clearance and offers better traction, some 4WD owners fall into the trap of making endless modifications to off-set the drawbacks of using bigger tyres. If you’re in doubt about increasing the size of your tyres, it’s best to speak with experienced professionals who can talk you through the process and what you can expect.
For any further information, speak with the 4WD specialists at TJM Australia by phoning their staff on 07 3865 9999.