Do tires affect fuel economy?

You wouldn’t normally think that tires have any effect on fuel consumption. They are, however, responsible for a third of the fuel consumption of any vehicle. With the prices of petrol reaching new heights, pollution becoming a greater concern and fuel efficiency being the top priority for most drivers, we simply cannot afford to overlook their role.

To understand the role of tires in managing fuel consumption, we need to understand the 5 forces that are acting on any vehicle when it moves on the ground. First is inertia, which is the tendency of a vehicle to resist a change in its velocity. Second is gravity, which is the weight of the vehicle and is simply inescapable. The third force is aerodynamic resistance. Cars are already being designed to minimize its effects as much as possible. The internal force of friction between the various moving parts of the car like the engine and the driveshaft is the fourth force. This gets countered by the engine oils and lubricants used throughout the parts of the vehicle. But for the most part, fuel is consumed to overcome all these resistances.  

The fifth and the most difficult to understand force of them all, is rolling resistance. Rolling resistance is the result of the tire changing its shape under the load of the car and the many forces acting on it, as it moves on the ground. These forces distort the shape of the tire. Tires being viscoelastic, regain their shape as they move out of contact with the road surface. The energy used in distorting the tire comes from burning fuel. But when the tire regains its shape, some of the energy ends up getting wasted in heating the tires.

While this distortion is necessary for providing grip on the road surface, rolling resistance’s effect in increasing fuel consumption cannot be ignored. How do we then control rolling resistance? Tires with lower weight will tend to have lower rolling resistance. But mostly this is achieved by narrowing the width of the tire and increasing the height of the sidewall, leading to lesser grip. At the same time, a lower sidewall height leads to a more rigid tire and thereby a lesser amount of rolling resistance but also decreases comfort. The width of the tire also contributes towards aerodynamic resistance, so much so that a decrease in 1 cm of tire width can lead to 1.5% lower aerodynamic resistance. The tread pattern, tire wear and the compound used in the construction of the tire, determine how effectively the rolling resistance is distributed.

Tire pressure is another obvious factor. Too low tire pressure leads to worse grip. A deficit of 0.3 bar of pressure translates to an astonishing 6% higher rolling resistance. The road surface itself affects rolling resistance, as one study claims that asphalt generates 24% greater rolling resistance than concrete. You yourself can remember the time your car struggled to find grip on sand and we don’t even have to start talking about wet roads.

Tires do have a large effect on fuel economy. But they have a really important role to play. They need to be safe, grippy, long lasting and provide sufficient cushioning. They also have to be affordable to buy and last a long time. There are tires that are specifically designed to have a low rolling resistance that claims as much as 6% decrease in fuel consumption. But many qualities that decrease rolling resistance end up compromising on the other needs. These tires may also be a little more expensive than standard ones.

Of course, there are other factors that go into determining your car’s thirst for fuel. We haven’t even touched upon those angles and driving styles. But when it comes to buying tires, we have to be aware of the balancing act between comfort, grip, cost, usable life and fuel economy. At the very least, buy tires that are specific to the needs of you and your vehicle and keep an eye out for their condition.