Rolling resistance is a very important force in the set of forces you need to overcome when riding a bike.
You need to overcome gravity when going uphill, but you also gain gravitational potential energy, which you will use fully when going downhill. In a 2020 article on bicycle aerodynamics published in the Journal of Wind Engineering and Industrial Aerodynamics, Malizia and Blocken pointed out that when riding a bicycle at speeds of more than 40 km/h on a flat road, about 90% of the resistance you overcome is air resistance, which is why road cyclists are fascinated by all things related to air. In addition, the friction between the tire and the road (or rolling resistance) is the main force you need to overcome before you can start riding and ride faster.
Below we'll tell you what rolling resistance is, how to measure it, and what factors affect it. While rolling resistance is usually considered a road bike issue, we'll also explain why it's important for mountain bike and gravel riders, too. We'll also introduce the three best road tires we found in our own testing that have low rolling resistance.
What is rolling resistance?
According to tire manufacturer Schwalbe, rolling resistance is the energy lost as a tire rolls. This energy loss comes from several sources, chief among them being energy lost through deformation of the tire. There is also friction between the tire and the road, which is why riding on smoother tarmac is much easier than on gravel or off-road.
Deformation, or relative movement of the tire, results in heat and sound generation, as well as energy loss in the system. In cycling, tire width, diameter, and tire pressure all affect tire deformation. Other factors, such as tire flexibility and the rubber compound used in the tread, also play a role.
Replacing some of the carbon black in the tire compound with silica can reduce energy losses from relative movement, thereby reducing rolling resistance, which is why high-performance tires often include silica. Graphene is said to have a similar effect, and Vittoria has added graphene to its high-performance tires.
If you compete in time trials or races, you may be willing to sacrifice tire life and puncture protection for more speed. Competition tires often have thinner treads and sidewalls, and may not even include puncture protection. On the other hand, if you ride on rough roads, or simply hate having to patch punctures mid-ride, you might be willing to accept the added rolling resistance for an extra layer of puncture protection for better puncture protection, grip, and increased tire life.
Why is rolling resistance important?
Rolling resistance is one of the most obvious forces that slow you down, and it's also one of the easiest to address. Aside from air resistance, rolling resistance accounts for a large portion of the resistance you experience while riding, and even exceeds it at lower riding speeds.
Almost every cyclist wants to ride faster, farther, or with less effort, and reducing rolling resistance is one of the simplest and cheapest ways to achieve that goal. As Schwalbe points out, "Cyclists have very limited physical energy, and they want to use that energy as efficiently as possible."
Choosing a tire with lower rolling resistance is relatively inexpensive, but it can also optimize your existing riding conditions and routes, which are free to you.
How to test rolling resistance?
The tire to be tested is mounted on a test wheel and inflated to a predetermined pressure. The tire is placed in contact with a test roller, which applies pressure to the wheel from above, simulating the deformation of the tire by the rider's weight.
The system determines the rolling resistance of the tire by measuring the excess power or torque required to keep it spinning at a specified speed. Multiple repeated measurements are usually performed to ensure accuracy and repeatability, and there is usually a warm-up period before the measurement to ensure that the system and tire are balanced. The rolling resistance of bicycle tires is usually expressed in Watts, a unit familiar to riders and enthusiasts, although there are other units for expressing the measured value. For example, the rolling resistance coefficient or Crr is the force required to overcome the rolling resistance divided by the wheel load, usually expressed in N/kg.
Comparison of rolling resistance between clincher, tubeless and tubular tires
One factor that affects the rolling resistance of a bicycle tire is the friction between the inner tube and the outer tube, which occurs when the tire deforms under load. One review specifically tests the rolling resistance of a tire and other factors. They tested the rolling resistance of 10 different TPU, latex and butyl inner tubes with a 25mm Continental GP5000 STR outer tube, and also compared them with tubeless tires.
The conclusion was that the rolling resistance increased by 0.2-3.8W when using an inner tube over tubeless tires. Latex inner tubes had the least impact on rolling resistance, and most TPU inner tubes performed better than butyl inner tubes. The final conclusion was that tubeless tires are the most efficient, and if you want to use inner tubes, use the non-tubeless version of the GP5000 clincher tire, which is faster, lighter and cheaper.
Tubular tires are actually the same as clincher tires, but tubular tires are more expensive, and their rolling resistance may be comparable to that of clincher tires with latex inner tubes.
Cotton tires also help reduce rolling resistance. The type and amount of glue used and the length of time the glue dries will affect the results, so it is impossible to draw any clear conclusions from the comparison test.
In general, the difference in rolling resistance between tubeless tires and latex or TPU innertubes is small, so you can choose according to your preference. In addition, tubeless tires provide additional protection against punctures, and the presence of self-sealing fluid allows you to ride home even if you get a puncture in most cases.
How does rolling resistance vary with tire width?
We tested two different widths of the Pirelli P Zero Race TLR (26mm and 30mm) to see if the wider tire is faster. The answer is: it depends.
On indoor rollers, when both tires are run at the same pressure, the 30mm tire requires less power to maintain the same speed. This is because the wider tire deforms less at the same pressure due to its wider and shorter contact patch. When the actual tire pressure is adjusted to the same level as required, the narrower one is more efficient. In theory, if you can perfectly adjust the tire pressure of each width to maintain the same contact patch, the rolling resistance should be the same.
But in actual riding, on good roads, wide tires are no slower than narrow tires, and on rough roads that require compliance and grip, wide tires are faster, where they provide more cushioning compliance and a larger cornering surface area. This is why many elite gravel riders choose ultra-wide tires to participate in high-difficulty off-road races such as Unbound.
So you should choose the tire size based on the terrain you ride and your riding goals.
Is rolling resistance important for manufacture mountain bikes and gravel bikes?
The short answer is: yes, but not as much as on a road bike. For many mountain and gravel riders, rolling resistance may not be the first priority. A lighter or thinner tire with less rolling resistance may be more prone to punctures, which is not worth the compromise for endurance racing or difficult trails.
One area where mountain bikers may be willing to sacrifice some grip for lower rolling resistance is in XC racing, where fast passing is an advantage, of course, the route cannot be too difficult, and the same is true for gravel.
So for most mountain and gravel riding, grip and puncture resistance are more important than low rolling resistance.
It's worth noting that the difference in rolling resistance between most of the tires tested was minimal. There are many other factors that can affect the efficiency of a tire on a bike, including the wheel pressure you use, the internal width of the rim, and the combined weight of you and your bike.
The bottom line is that there is a trade-off between rolling resistance and other factors like aerodynamic drag, durability, and grip, and you need to make that trade-off when deciding which tire to use and in what conditions and at what pressure.
