What Is Rolling Resistance In Tires?
Rolling resistance in tires is the energy required to keep a tire rolling at a constant speed over a surface. It affects fuel efficiency and vehicle performance. Hysteresis, the tire’s deformation and recovery as it contacts the road, is the primary cause of rolling resistance. Rolling resistance combines forces like vehicle weight, road friction, and air drag, opposing forward motion​​​​​​​​.
Factors that Contribute to Rolling Resistance In Tires
Several factors influence a tire’s rolling resistance:​​​​​​​​​​
- Wheel Radius and Speed: Wheel radius and the vehicle’s forward speed influence rolling resistance. A smaller wheel radius can increase resistance due to more frequent deformation cycles per distance traveled.
- Tire Material: Different fillers and polymers improve traction and reduce hysteresis. Replacing carbon black with silica–silane reduces rolling resistance. Exotic materials like nano-clay and specific solvents can also lower resistance in high-performance tires​​.
- Tire Dimensions: The flex of sidewalls and tire contact area affect resistance. Wider tires under the same pressure flex less in the sidewalls, leading to lower rolling resistance but potentially higher air resistance​​.
- Tire Inflation: Proper inflation is critical. Under-inflated tires increase sidewall flexing and resistance, leading to overheating and potentially hazardous conditions. Over-inflation can cause the tire to lose traction and increase overall rolling resistance​​.
- Tread Thickness and Shape: Thicker, deeper, more contoured tread increases rolling resistance. Tires with minimal tread depth, exhibit lower rolling resistance​​.
- Temperature Effects: Rolling resistance decreases as temperature increases within a certain range. A temperature rise from 30°C to 70°C can reduce rolling resistance by 20-25%. This change is often leveraged in racing to increase tire friction rather than to decrease rolling resistance
Benefits of Low-Rolling Resistance Tires
Low-rolling-resistance tires are designed to improve vehicle fuel economy. They offer a potential fuel savings impact of up to 10% for drivers, although the average savings is around 3%. These tires require less energy to maintain forward motion at speed, leading to increased fuel efficiency​​​​​​​​​​.
Drawbacks to Low-Rolling Resistance Tires
While low-rolling resistance tires offer benefits like improved fuel efficiency, they also have drawbacks. The design elements that reduce resistance might compromise other tire aspects, such as tread depth.
Low rolling resistance tires have reduced tread depth which means they have a shorter tread life compared to other tires. This could also affect the tire’s overall performance in various driving conditions.
Rolling Resistance Coefficient (RRC)
The rolling resistance coefficient (RRC) measures the force needed to overcome a tire’s deformation while rolling. Expressed in kg/t, it depends on factors like tire construction, materials, air pressure, vehicle speed, and road conditions. RRC remains constant at low vehicle speeds but slightly increases as speed rises.
Is It Possible to Avoid Rolling Resistance?
While it is not possible to completely avoid rolling resistance, you can minimize it to some extent. Rolling resistance arises from fundamental physics principles, like friction and deformation, essential to tire operation. However, it can be minimized through technological advancements in tire design, materials, and maintenance practices like proper inflation.
Are Low-Rolling Resistance Tires Worth It?
Low-rolling resistance tires are worth considering for their fuel efficiency benefits. They reduce the energy needed for a vehicle to move, leading to fuel savings. However, the worthiness depends on individual priorities, like performance preferences and driving conditions. If tread depth and lifespan are not your priority, you should definitely consider tires with low rolling resistance.
Do Wider Tires Have More Rolling Resistance than Narrower Tires?
Wider tires typically have lower rolling resistance than narrower ones at the same pressure, as they flex less in the sidewalls. However, they may have higher air resistance. The overall impact on vehicle efficiency depends on a balance between rolling and air resistance, along with other factors like vehicle weight and tire tread.
Does Tire Diameter Affect Rolling Resistance?
Tire diameter does affect rolling resistance, but the effect is generally minor, especially on hard surfaces and within a limited range of diameters. Larger diameter tires may have slightly lower rolling resistance due to a decreased deformation frequency per distance traveled.
However, the overall impact of diameter on rolling resistance is less significant compared to other factors such as tire material, tread pattern, and inflation pressure.