Why You Should Always Know Your Tires' Rolling Resistance

If there's one component on any vehicle which influences its handling characteristics more than anything, it's the tires. Tires are, in ideal situations, the only parts of a car that touch the ground, bearing the full weight and all the physics associated with driving. A tire must accelerate, stop, and turn predictably and reliably for a vehicle to feel consistent, and a large chunk of this rests in the tire's rolling resistance. So what is rolling resistance, and why is it so important to how a vehicle handles?

The short definition is that a vehicle's rolling resistance is determined by how easy it is to keep the wheels turning. A car with low rolling resistance requires less energy to maintain a constant speed versus a car with high rolling resistance, thus it'll be more fuel efficient. For instance, tires with 30 percent lower rolling resistance will lower fuel consumption by as much as 3% to 5%. There are various ways to manipulate rolling resistance, such as choosing the correct tire pressure for your application.

High and low rolling resistance each feature numerous benefits and drawbacks. Namely, tires with higher rolling resistance generally boast higher grip levels, since there's more adhesive force contacting the road at any given time. This proves particularly vital in specialized applications like drag racing, which usually run far lower tire pressures to maximize the tire's contact patch. Let's take a look at some other factors influencing rolling resistance and what you need to know to lower yours.

Rolling resistance directly ties in with numerous factors, the first and most obvious being the tire itself. Typical automotive tires are designed to adhere to a road surface, utilizing elements like tread pattern, air pressure, rubber composition, and tire width to influence grip levels. For instance, a softer, wider tire provides more grip than a harder, narrower tire, which is why F1 tires are so smooth, and so different to normal passenger car tires.

But no matter what cars they're fitted to, all tires obey the laws of physics, which means that they must contend with the friction generated with the road surface trying to slow them down. Hence, the more material sticking to the road, the greater the rolling resistance, and so wider tires feature greater rolling resistance than narrow ones. That's one reason why racing bicycles use wafer-thin tires, they're easier to pedal because they have less friction resisting the rider.

Other factors are just as important, though not as easily understood, like the internal components of a car's wheel hub and its running gear. A wheel hub is the physical link between the car's wheel and the axle. It utilizes several low-friction components to help minimize rolling resistance, such as smooth roller bearings on which the assembly rotates. 

Similarly, axle shafts run to a car's differential or transaxle, further fighting against the car if not properly maintained. There may also be a driveshaft, transfer case, and so on, all cumulatively providing some form of mechanical resistance when there's no power going to the wheels. Therefore, making sure that all bearings are in good shape helps minimize a vehicle's rolling resistance.

As stated previously, one primary benefit of lowering roll resistance is improved fuel efficiency. This is because it takes less work for the engine to rotate tires with less friction applied. Think of how easily a tire is rotated in the air with no friction, as opposed to being on the ground. This is achieved through two primary methods, a narrower tire and higher tire pressures. 

With greater air pressure, a tire is less resistant to the weight pressing it down, so it deforms less readily, and thus has less rubber on the road. However, it's better to use low pressures in specific circumstances, and it's sometimes better to air down your tires when off-roading. Another benefit to high resistance is improved braking performance — with more rubber on the road, there's more tire available to bite and stop the car.

Because it's a trade-off between grip and efficiency, major tire manufacturers create different tires to suit different vehicle types. The most fuel efficient cars you can buy today typically feature tires with lower rolling resistance to help improve economy, sometimes drastically so, with some all-season tires featuring a third less rolling resistance than other types. 

However, prioritizing a tire based on this factor alone is potentially hazardous because they typically have less grip in adverse conditions and worse maneuvering characteristics. Ultimately, there must be some rolling resistance to help redirect a vehicle, otherwise all cars would simply continue in a straight line. So the less resistance, the less responsive it'll be in the turns. As such, choosing the tire best-suited to your ride is vital to its overall handling characteristics.