It might seem to some drivers that all tyres are just tyres, but there are many different types, even for the same vehicle and wheel size. There are also several main differences between regular tyres and 4×4 tyres. There are also different types of 4×4 tyres.
What most people call 4×4 tyres are actually 4×4 off-road tyres. But there’s also 4×4 all-terrain and 4×4 on-road tyres.
First, we’ll cover off-road tyres and look at the differences between them and regular tyres.
These are tyres which are designed to retain grip on mud, dirt, grass and snow. If you look at them, you’ll notice that the tread on these tyres is deep, with larger gaps in-between the tread pattern. This allows the tyres to retain friction with the ground in these adverse conditions.
With a road tyre on a muddy surface, its shallow tread would quickly become clogged with mud, leading to a loss of friction. Friction is crucial for grip. Without friction with the road surface/ground, the tyre would simply spin. On muddy terrain, as the tyre spins it will dig the vehicle’s wheel into a hole; meaning that the task becomes even harder.
On an off-road tyre; the much deeper tread-depth is much harder to clog-up. And even when these gaps in the tread pattern are full of dirt and mud; there’s enough rubber in contact with the ground to retain enough friction to move the vehicle. In fact, with off-road tyres in general; much more rubber is in contact with the ground at all times than with a regular tyre.
Of course, with more rubber in contact with the ground and much more friction being created this also has two major flaws:
1) When on a normal road surface they will become worn much faster than a tyre designed for road use. Off-road tyres driving on a normal road surface are creating much more friction than is actually needed to propel the vehicle forwards.
2) They actually create so much friction that it slows the vehicle down considerably, leading to excess fuel consumption as well. The greater the friction between the vehicle and the road; the harder the engine will need to work to move the vehicle at the same speed.
Despite what manufacturers of off-road 4×4 tyres may promise; these are the trade-offs of using off-road tyres. They are not as good as road tyres on a normal tarmac surface. No matter how good the tyres are; the laws of physics still apply. But they are far superior to road tyres on the correct surface.
If you’ve ever witnessed a vehicle driving on a normal road surface with off-road tyres you will notice a loud, persistent whining. This is the sound of the rubber in contact with the road, and what you’re actually hearing is the rubber being worn away by the road surface. Yet on the correct surface they are silent. In general, when tyres are doing the job they’re designed to do; they will not wear as quickly as during incorrect use.
Next we’ll talk about the difference between 4×4 tyres and normal tyres in general.
The drive train on a 4×4 vehicle is different to that of a normal vehicle. The power comes from the engine, through the gearbox and into a transfer box. From here it travels down a prop-shaft to a differential unit. Commonly referred to as a “diff”. From this differential unit; the power is then distributed to the wheels via drive-shafts. There are two differential units on a 4×4, a front and rear diff.
Essentially this means that all wheels are working rather than having two passive wheels. They are all sharing the task of moving the vehicle. This is why it’s harder to get stuck when going off-road in a 4×4 vehicle as opposed to a front or rear-wheel drive vehicle. They are sharing the load in a way that many vehicles do not, so it’s a good idea to fit tyres recommended for use on your vehicle. Fitting tyres meant for a 2-wheel drive car can cause problems with wearing and grip.
Fitting the exact tyre recommended by your manufacturer is good practice anyway and it’s a good habit to get into. People often like to modify their vehicle to make it their own; but they don’t have the benefit of the insight that has come with spending millions of dollars on testing. Rarely is it the case that fitting the incorrect tyres to the car will actually improve the performance. It’s more likely that they will become worn.
Now let’s talk some more about the main different types of 4×4 tyres we’ve yet to mention.
4×4 All-terrain tyres.
These are designed for both on-road and off-road use. While they may not be as good as either on-road or off-road tyres at their specific task; they are a more ideal balance between the two. They will not really excel at either task, but they can be driven off-road reasonably well and they can be driven on-road without the excessive wear and fuel consumption of off-road tyres. But they will become worn more quickly than on-road tyres.
4×4 On-road tyres.
These are road tyres specifically designed for 4×4 use. In the case of a larger 4×4 such as; a Landrover Discovery; they will typically feature slightly larger tread-depths than on a front-wheel or rear-wheel drive car, because the manufacturers presume that the vehicle will be used off-road at some point. On these large 4x4s the standard on-road tyres are more typically what we refer to as all-terrain tyres on other vehicles.
On a 4×4 saloon or hatchback car, the on-road tyres will look much the same as on any other car, though they may have tread patterns more suitable for the occasional off-road use. They will also often be a uniform size, whereas 2-wheel drive wheels can sometimes differ in size between front and rear wheels.
So there we have it. The main difference between 4×4 tyres and regular tyres is that a 4×4 is usually designed to go off-road, and the tyres (even the standard type) are as well. Off-road 4×4 tyres are totally unsuitable for on-road use. If you live in a rural area that requires off-road tyres, but you also do a lot of driving on tarmac; it would be a good idea to invest in all-terrain tyres instead. It’s a rare occurrence that you may require the extra capability that off-road tyres will offer over that of all-terrain tyres. So, it may make more sense to go for all-terrain tyres except in the very worst conditions.
ABOUT THE AUTHOR
Sophie Smith is a trainee engineer from Brisbane, Australia.