Detailed Explanation of Rolling Resistance
Rolling resistance is drag on your bike’s forward momentum. It has three causes: casing deformation, ground deformation, and suspension losses. CushCore reduces energy loss in all three categories.
Tire casing deformation happens when the tire flattens out under the rider’s weight. As the wheel rolls, the tire is continuously deforming where the tire first touches the ground and reforming where it looses contact with the ground. Deforming the tire saps a little energy from forward momentum; reforming gives a little back in the form of a “push” due to the tire’s elasticity. However, it’s a net loss, and the asymmetry of energy consumption and return is called hysteresis. Tires with flexible, supple casings require less energy to deform and re-form — which explains why handmade road racing tires with delicate silk or cotton casings generally have the lowest rolling resistance. It also partially explains why tires with stiff casings, like downhill racing tires, are such a chore to pedal.
CushCore allows riders to run tires with fast-rolling, supple casings without compromising lateral stability or impact protection.
Ground deformation means the riding surface (as opposed to the tire) deforms and siphons energy from the system. When tires sink into soft ground, they have to push through a wake of soil at the front of the tire. Most mountain bikers are familiar with ground deformation losses as the frustrating feeling of pedaling through loose sand.
CushCore allows low tire pressures to be used without risk of flat tires or stability problems. Lower pressure results in a larger contact patch, which aids flotation on soft soils and reduces the energy lost to ground deformation.
Common understanding of friction and casing deformation losses suggests that skinny tires at very high pressures would produce the lowest rolling resistance. This is in fact true for perfectly smooth surfaces (like an indoor velodrome), but the situation changes in the real world where every riding surface has bumps, cracks, and obstacles. “Suspension losses” describes the energy lost to shock and vibration from riding over these obstacles.
A report in Bicycle Quarterly by Jan Heine demonstrated that wider road bike tires produced lower rolling resistance than equivalent skinny tires. The differences were much larger than expected: the fastest tire in the test rolled 20% faster than the slowest tire in the test. A 20% drag reduction is about ten times the advantage offered by high-tech aerodynamic wheels.
In a subsequent test, Heine compared rolling resistance on smooth asphalt to grooved asphalt (“rumble strips”). The bike rolling on smooth pavement required an average of 183 watts to maintain 16 mph. The same bike rolling on the rumble strips required 473 watts, more than two-and-a-half times the power, to maintain the same speed. In further testing, Heine was able to improve rough road performance by using (1) wider tires, (2) lower tire pressures, (3) tires with supple casing, and (4) adding suspension elements to the bicycle (such as a RockShox suspension fork).
Suspension Losses in Mountain Biking
The research above shows that even relatively small bumps have a significant effect on rolling resistance. This effect is magnified with trail obstacles such as rocks and roots.
When a bicycle wheel strikes a bump, it transmits a force to the wheel in line between the point of impact on the tire and the wheel hub. This force has a vertical component that pushes the bicycle upward, and a horizontal component that pushes the bike backward. This backward “push” is a form of rolling resistance.
For example: a bike and rider roll into a 75mm (3″) tall bump. This relatively humble obstacle subjects the bike and rider to a punishing 709 Newton impact force. That’s about the same as a 72 kg (159 lb) weight, a considerable portion of which goes directly into slowing down the bike.
Force required for a wheel to overcome a bump:
The horizontal component of impact force is opposite the direction of travel.
Effective suspension (both tire and wheel suspension) would be a great advantage in this example. Suspension not only makes the ride more comfortable, it helps preserve forward momentum by isolating the mass (bike and rider) from the impact force (rock). It’s faster and more comfortable at the same time.
CushCore’s tire suspension characteristics are proven to be superior to other tire inflation systems. These suspension advantages translated into reduced suspension losses and less rolling resistance on rough terrain.