There are many things that affect fuel economy in a 4WD with regards to tyres. One of the more common questions is whether changing tread pattern affects fuel economy.
If you don't know how to work out your fuel economy properly, have a look at this; How to work out your 4WD's fuel economy.
Changing your tread pattern to one that is more aggressive will almost always result in more fuel being consumed, although there are lots of variables to consider.
OEM or factory tyres
You'll notice that all brand new 4WD's come with the same style of tyre. It's non aggressive, smooth and is known as a road terrain tyre. Ever wondered why they supply these, given they are the worst tyres off road? It's pretty simple; they are quiet, smooth, comfortable, handle well on bitumen and .... they are the most fuel efficient.
How do tyres affect fuel economy?
Tyres create friction as they rotate, through the flex between the tyre itself and the road. The more that the tyre deflects the higher the rolling resistance, and thus the higher fuel consumption. Ever noticed when you let your tyres down in a 4WD the engine feels like it has to work harder?
That's because it does; you literally have to make the engine work harder to overcome the additional rolling resistance. Its the same on a beach; your rolling resistance is hugely increased because of the sand.
Rolling resistance increases (and as a result so will your fuel consumption) through the following changes:
- Increased tyre weight(which it will when you go from passenger tyres to light truck, increase width or height)
- Increased diameter of your tyre
- Decrease in tyre pressures
- Increase in weight on the tyre
- Decrease in tyre aspect ratio
- Poor wheel alignment
The other major factor to consider is Aerodynamics. If you imagine air rushing over a smooth tyre, at 100km/h compared to air rushing over a chunky tyre, like the various mud terrain tyres on the market, its pathway is disrupted further, and results in the engine having to work harder to keep the tyres turning.
Likewise, when you install a rooftop tent, or a big bull bar, the air is going to find it harder to get past your 4WD, especially at higher speeds.
There is a lot money spent on designing tyres that maximise traction but have good aerodynamics, along with various other requirements. However, like everything, its always a compromise; you want fantastic traction, it comes about by having an aggressive tyre, which in turn goes against good aerodynamics.
Thinking about changing your tyre tread pattern?
There's nothing wrong with changing your tread pattern. The tyres you run should reflect the way in which you use your 4WD. However, it'd be great if everyone knew what to expect when changing their tyre tread pattern. I've had people tell me that their fuel economy has gone up by 2 litres per hundred kilometres, just from going from a normal road terrain tyre to all terrain. That's a pretty hefty change in your fuel bill; perhaps you'd reconsider the change if you really knew what it was going to do.
In essence then, the more aggressive your tyres, the more fuel they are going to use. That said, millions of dollars are being poured into research and development of 4WD tyres that are not only amazing off road, but reduce your fuel consumption. Bear in mind that the amount of fuel you use is not directly comparable from vehicle to vehicle. An engine with more power is likely to see less of a difference in fuel consumption as the engine won't have to struggle much more.
Don't believe everything you hear
I tend to take peoples fuel economy figures with a grain of salt, because a large percentage don't know how to work it out, or don't work it out accurately. Tyre sizes vary from manufacturer to manufacturer, so unless you are factoring in speedometer error, filling the tank full each time and calculating it correctly, you are wasting your time. That, and tyre pressures should vary considerably from vehicle to vehicle, and that plays a big role in fuel economy.
What else affects your 4WD's fuel economy?
Dirty filters and sensors
If you air or fuel filters are dirty, you will get worse fuel economy. Likewise, any sensors such as oxygen and mass air flow will make the vehicle use more fuel if they are dirty or faulty.
In almost every case, accessories that bolt onto the outside of your 4WD will decrease your fuel economy. Bull bars, rear bars, roof racks, awnings, antennas and anything else you add hinders airflow over the vehicle when you are driving, and results in more fuel being consumed.
As above, anything you add to your 4WD also increases the weight of the 4WD. When you pick up a 20kg bag of salt, its harder to move around. The same principle applies to your 4WD; anything you add to it requires the engine to work harder to push it along.
Your right boot
The way you drive plays a massive impact on how much fuel you use. If you find yourself braking hard, and accelerating quickly, you have room for improvement. The gentler you drive, the less fuel you will use.
Something that people don't consider is the quicker you go, the more fuel you use. If you sit at 95km/h, you will use much less fuel than 100km/h, and likewise the difference from 100 - 110km/h can easily be 2 litres per hundred km. This is obviously vehicle dependant, but its something you should consider; arriving half an hour later to save yourself a few bucks is sometimes worth it!
Again, the more weight your vehicle has to move, the more fuel it is going to use. Tow a trailer and your fuel consumption will go up.
Is it worth it?
That's a question only you can answer. To me, traction is more important than a bit of extra fuel, so I run BFG KM2 tyres. What do you think? What tyres do you run?