Five Things to Know About Fuel Economy and Rolling Resistance

Quick Links: 1. What is Rolling Resistance? | 2. Why Does Rolling Resistance Require So Much Energy? | 3. What Factors Influence Lower Rolling Resistance?| 4. Can Fleets Address Rolling Resistance Without Purchasing All New Tires? | 5. How Do Balanced Tires Impact Fuel Economy?

In today’s fast-paced world, fleet owners must be aware of the many factors that contribute to the success of an effective, cost-efficient fleet. Fuel economy, defined by the rate of fuel consumption by a vehicle in travel, plays an increasingly prevalent role in driving the long-term success of a demanding fleet.

Particularly for larger, national fleets where trips extend beyond state lines – but still applicable for smaller fleets that strive for longevity and require regular use – it’s imperative that fleet owners have a good understanding of the impact that any factor can have on fuel economy.

Let’s take a look at some important facts regarding fuel economy, rolling resistance, and modern industry approaches to guaranteeing operationally efficient fleets.

1. WHAT IS ROLLING RESISTANCE?

The concept of rolling resistance extends far beyond a commercial use definition, in fact, rolling resistance is experienced in bicycles, automobiles, and any other use in which a wheel, or tire, travels across a solid surface.

You can think of rolling resistance as the rolling friction or drag that resists the motion of your vehicle, or truck’s, tires to roll at a given speed.  We tend to think of tire movement as a fairly cohesive, limited movement. However, the movement of tires, and the way in which they react to changing surfaces, is actually quite complex. As tires roll, they continuously change shape to allow the portion of the tire that is touching the surface to flatten. When this section of the tire flattens, it creates a deformed shape at the tire footprint– this is the adaptability that allows your vehicle to continue moving at a consistent speed.

Like all forms of movement, however, rolling resistance requires energy – lots of it – all to assist with the tire’s need to change from a defined to relaxed state, and back again. Let’s explore the energy required in the process of rolling resistance.

2. WHY DOES ROLLING RESISTANCE REQUIRE SO MUCH ENERGY?

A great way to think about the relationship between tire rolling resistance and energy consumption can be considered with a classic example of riding a bike. Think back to a time when you rode a bike that suffered from one or two tires that were under-inflated, or perhaps even flat. As you pedal on a bike with an underinflated tire, you are forced to pedal harder and faster, pushing back against a force that you can’t see – but you can certainly feel in your muscles the next day!

The force in action is one called “hysteresis”, or the amount of energy that is lost when the tire meets the road surface. In the example with underinflated tires, hysteresis plays a greater role, as the tires are forced to work harder to change shape. In this situation, the bicyclist is forced to provide more mechanical energy, as energy is a required component of rolling resistance.

While we can directly feel the impact of underinflation of energy use as a bicyclist, it’s often harder to identify when you’re driving a car or truck. For both of these vehicle types, understanding energy consumption for rolling resistance is even more important. While we can feel when we’re getting tired of pedaling, and we can easily control the output of energy and effort, it can be a challenge to tell when wheels on trucks and cars are struggling due to the friction of increased rolling resistance.

While trucks are designed to allocate energy expenditure across all mechanisms, nearly 30% of the energy that makes it to the tires is given up by friction, or hysteresis. If your fleet is suffering from excessive fuel consumption that you think could be due to more than mileage, you might just find your answer in the correlation between tire rolling resistance and energy, or fuel, consumption.

3. WHAT FACTORS INFLUENCE LOWER ROLLING RESISTANCE?

The first solution is, of course, to ensure that all tires are properly inflated prior to beginning your truck’s next journey. Not only is adequate inflation key to maximizing the time that your trip will take, but it will also provide more longevity from each tire.

While pretty much everyone has justified riding a bike that could use a little more air in the tires, there is significantly less wiggle room for commercial vehicles that travel across busy highways and roads that don’t accommodate for pulling over. If you need further motivation to keep your tires inflated, a 0.5-1% increase in fuel consumption is the result of vehicles that run on tires which are underinflated by 10 psi.

Next, the design of the tire itself can play a pivotal part in decreasing tire rolling resistance. Certain types of rubber equate to less hysteresis, meaning smaller amounts of energy are required to change the tire’s shape. A few materials have been tested and proven to reduce rolling resistance, including silica: which enables the truck to experience decreased rolling resistance without losing required traction.

For many fleets, purchasing brand new tires, however, is not a viable expenditure in the near future. In these cases, a common question arises: how can we achieve a better fuel economy without sacrificing what we love about our existing tires, and how do we find a middle ground?  Next, we’ll review a few other options that can achieve the goal of lower rolling resistance with the current tires in your fleet.

4. CAN FLEET ADDRESS ROLLING RESISTANCE WITHOUT PURCHASING ALL NEW TIRES?

At IMI, we hear this question quite often from fleets that we work with. In many fleets, particularly those that are owned by larger companies with hundreds, or thousands, of vehicles, it can cause quite a headache to consider the transition to a brand new type of tire.

In addition to the logistical nightmare, did you know that the last one-fifth of a tire’s tread actually uses 6.5% less fuel than new tread? Rather than replacing tires prematurely, we can increase savings by extending the life span of our tires – a huge factor in boosting fuel economy.

Fortunately, there are other, equally effective solutions in the industry that will provide assistance in decreasing resistance. In addition to ensuring proper tire inflation, correct wheel alignment can also influence rolling resistance. When axles are improperly aligned, the wheels end up turning inward or outward as the vehicle moves forward, preventing the truck from traveling in a straight line. The angle created by the misaligned wheel in relation to the road beneath requires more force or energy, to keep the truck moving forward at a steady rate. Therefore, wheel alignment directly impacts the rate of fuel consumption.

If your tires are inflated, and the axles are properly aligned, the next factor to evaluate is tire balance.

5. HOW DO BALANCED TIRES IMPACT FUEL ECONOMY?

At the start of a trip, drivers should ensure that all tires on the vehicle are equally equipped for the trip ahead. However, anyone in the commercial trucking industry knows that not all trips are created equal, and not all tires are created equal, either.

Throughout a truck’s journey, the tread may wear unevenly due to continuously changing road conditions, driver speed, load weight and more can all impact tread wear. If you’re a truck driver, you’ve likely experienced the vibration that can occur due to unbalanced tires, and if you’re a fleet owner, you’re likely aware that uncomfortable rides for your drivers contribute to increased driver fatigue.

When it comes to fuel economy, however, we can think of the value of wheel balancing as an initiative designed to evenly allocate energy expenditure. Suppose, for example, we place two oranges with the same exact weight on opposing sides of a weighing scale. The scale should remain an even, unmoving piece of equipment: steadily holding the two oranges in place. If one weighs less than the other, however, it slowly tilts in favor of the heavier one – and if the goal is balance, it often takes a few tries to add and detract from each side before you find the perfect balance.

Trucks are designed to also reflect the goal of balance: if one tire on the left wears down unevenly, the vehicle has to extend more energy to correct the imbalance and contain the momentum. If you think about the effort required to find perfect balance on a weighing scale, consider the effort and energy required by a truck to maintain a semblance of balance across a long journey.

For fleets, adaptively balanced tires get up to 1 – 3% in fuel savings: an amount that equates to quite a lot of savings when you factor in the number of trucks within a larger fleet. Balanced tires may also last up to 40% longer than unbalanced tires, meaning you extend your tire’s longevity at the same exact time that you’re extending your fuel expenditures.

OTHER TIPS FOR FUEL SAVINGS IN COMMERCIAL FLEETS

In addition to a consideration for lowering rolling resistance, there are other steps that fleets can take to improve fuel economy. Here are a few tips with proven impact:

• Speed: Increasing speed by 1 mph results in a 1 mpg reduction of fuel economy
• Aerodynamics: Aerodynamic drag, or wind resistance, means energy loss at highway speeds
• Truck Load: For every 10,000 lb increase in truck load, fuel economy drops by approximately 5%
• Maintenance: Regular care and maintenance result in increased tire life and mileage before removal.
• Environmental Factors: Temperature and terrain directly impact fuel economy

If the mission is to improve your fleet’s fuel economy, it’s imperative to analyze all contributors: including operational, environmental, and design-related factors, to identify improvements that will positively impact your fleet’s rate of fuel consumption.

At IMI, we work with many fleets who have thoroughly tested all internal and external factors, and they often find that targeting tire rolling resistance was the mission that made the difference in the end.

Whether lowering rolling resistance is the solution your fleet currently needs, or perhaps you need to address one of the other factors first, it’s never too early to start saving your company valuable time, savings from fuel efficiency.

LEARN MORE ABOUT FUEL ECONOMY AND TIRE BALANCING SOLUTIONS 

We were so passionate about resolving common fleet issues pertaining to rolling resistance and fuel economy that we engineered an entire product around the concept.

EQUAL FLEXX is a scientifically-validated adaptive balancing solution that reduces wheel-end vibration and saves valuable energy for every truck within your fleet. For fleets who are looking for an adaptive wheel balancing solution that delays the purchase of entirely new tires, EQUAL FLEXX is a preferred solution.

We are more than our solutions, however. We are a team of experts in the commercial trucking industry who are always happy to answer your questions, provide recommendations, and discuss what’s new in the industry pertaining to improving fuel economy.

For more information on our recommendations or solutions, call us today at 855-535-7121, or fill out our online contact form here.