Rolling resistance is an extremely important power when riding a carbon bicycle. When riding uphill,the cyclists need to overcome gravity with great effort, and in the process, they also gain gravitational potential energy, which can be fully released when going downhill. When cycling at speeds exceeding 40 kilometers per hour on flat roads, about 90% of the resistance overcome is air resistance. That's why road riders are extremely fascinated by all factors related to air. In addition to air resistance, the friction between the tire and the road, known as rolling resistance, is one of the main facts that riders need to overcome. Only defeating them,then we can start bicycling smoothly and ride faster.

Now,Bola is explaining in detail what rolling resistance is, how to measure rolling resistance, and the factors that affect rolling resistance. Although rolling resistance is often considered a key consideration for carbon road bikes, Bola will explain why it is equally important for carbon mountain bikes and gravel bicycles.

What is rolling resistance?

Rolling resistance refers to the energy lost during tire rolling. There are multiple sources of energy loss, among which the most significant is the energy lost due to tire deformation. There is also friction between tires and the road surface, which is why riding on smoother asphalt roads is much easier than riding on gravel or off-road roads.

The deformation or relative displacement of tires can lead to the generation of heat and sound, as well as the loss of system energy. In the field of carbon fiber bicycles, the width, diameter, and air pressure of tires all have an impact on tire deformation. Other aspects, such as tire flexibility and the rubber ratio used in the tread, also play a role. If you participate in a time trial or race, perhaps you are willing to sacrifice tire life and puncture protection to increase speed. The tread and sidewall of racing bike tires are usually thin and may not even include puncture protection layers. On the other hand, if you are riding on rough roads or simply dislike repairing a tire blowout halfway, you may be willing to accept increasing rolling resistance to obtain an additional anti puncture layer for better explosion protection, grip, and longer tire life.

Why is the rolling resistance so important?

Rolling resistance is one of the most obvious forces that slow down cycling speed, and it is also one of the easiest forces to solve. In addition to air resistance, rolling resistance accounts for a large part of the resistance encountered during cycling, and even exceeds air resistance at lower cycling speeds.
Almost every cyclist desires to ride faster, farther, or more effortlessly, and reducing rolling resistance is one of the simplest and most cost-effective ways to achieve this goal. Choosing to replace tires with low rolling resistance is relatively cheaper, but it can also optimize existing riding conditions and routes, which are free for you.

How to test rolling resistance?

The tire is installed on the test carbon bike wheel and inflated to the predetermined pressure. At this point, the tire is in contact with the test drum, applying pressure to the carbon bicycle wheel from above to simulate the weight of the rider, causing the tire to deform.
The system determines the rolling resistance of tires by measuring the excess power or torque required to maintain a specified speed of rotation. Usually, multiple repeated measurements are taken to ensure accuracy and repeatability. And there is usually a warm-up period before measurement to allow the system and tires to reach equilibrium. The rolling resistance of bicycle tires is usually expressed in watts (W), which is a well-known unit for drivers and enthusiasts. Of course, there are also other units to represent measurement values, such as rolling resistance coefficient or Crr, which is the power required to overcome rolling resistance divided by the cabon road bike wheel, usually expressed in N/kg.

The comparison of rolling resistance among clincher,tubeless,and tubular tire

One factor that affects the rolling resistance of bicycle tires is the friction between the inner and outer tires, which occurs when the tire deforms under load.
When using inner tubes, the rolling resistance will increase by 0.2-3.8W compared to using tubeless tires. Among them, latex inner tubes have the least impact on rolling resistance, and most TPU inner tubes have better performance than butyl inner tubes. The final conclusion is that tubeless tires have the highest riding efficiency
Tubular tires are actually similar to clincher tires, but they are more expensive and their rolling resistance may be comparable to clincher tires that use latex inner tubes.
Generally speaking, the difference in rolling resistance between tubeless tires and latex or TPU inner tubes is small, and you can choose according to your preferences. In addition, the tubeless tire provides additional puncture protection, and the presence of self replenishing fluid allows you to ride home even if the tire is punctured in most cases.

How does rolling resistance vary with tire width?

On indoor rollers, when two tires are running at the same pressure, a 30mm tire requires less power to maintain the same speed. This is because under the same pressure, wider tires have relatively less deformation due to their wider and shorter contact surfaces. When the actual tire pressure is adjusted to the same level as required, narrower tires have higher efficiency. In theory, if the tire pressure of each width can be perfectly adjusted to maintain the same contact area, then the rolling resistance should be the same.
But in actual cycling, on better road conditions, wide tires are not slower than narrow tires, and on rough roads that require compliance and grip, wide tires are faster. In such road conditions, wide tires can provide more cushioning compliance and larger turning surface area. That's why many elite gravel riders choose ultra wide tires to participate in high difficulty off-road races such as Unbound.
So, you should choose tire size based on the terrain and riding goals.

Is rolling resistance important for carbon mountain bikes and gravel bikes?

For mountain and gravel riders, rolling resistance is important but not as important as road bikes. Many times, tires with lower rolling resistance are prone to blowouts and are not worth compromising on endurance races or difficult tracks. In specific scenarios such as XC races, mountain riders may sacrifice some grip for lower rolling resistance, but the trail cannot be too difficult, similar to gravel cycling. Overall, for most mountain and gravel cycling, grip and puncture resistance are more important than low rolling resistance.