A few weeks ago, we showed how rolling resistance and aerodynamics are affected by speed. Today, we look specifically at rolling resistance, discussing why lowering it is so important, and walking you through the math that shows why going faster increases rolling resistance.
The Watts Consumed By Rolling Resistance
Let’s review the equation that calculates the number of watts consumed by rolling resistance. By consumed, I mean the number of watts that are required to roll a wheel. When you pedal, you apply a number of watts to the pedals. For example, if you pedal with 200 watts and rolling resistance takes up 20 watts, this means only 180 watts of the energy you put into the pedals is used to move you forward. The 20 watts consumed by rolling resistance are lost as the kinetic energy is transformed to heat and sound. By lowering your rolling resistance, you will increase your speed since fewer watts are lost.
v = speed in m/s (i.e., “ground” speed)
m = total mass (kg) of rider + bike
g = 9.81 m/sec2
Crr = coefficient of rolling resistance
As a quick example let’s use the equation using the following numbers:
Crr = 0.0026
m = 81 kg
v = 10 mph or 4.4704 m/s
As you can see, 9.24W would be consumed by rolling resistance in this example. Remember this is only for one tire, so we need to double this value for total watt consumption due to rolling resistance.
You can also see that as velocity increases, so do the watts consumed by rolling resistance. This shows that the faster you go, the more watts are consumed by rolling resistance.
How Much Time Rolling Resistance Can Lose You
There are countless ways to come up with how much time a watt is worth. For our examples, we are going to consider that 1 watt is worth 5.28 seconds over a 40km distance. Knowing this, we can compare the time savings between two tires with different rolling-resistance values. The two tires we will compare are the Continental GP 5000 in a 25mm size at 100psi, and a Continental Gator Skin in a 25mm size at 100 psi. The Crr values for these tires were taken from bicyclerollingresistance.com
The tables below show the amount of time in minutes that is consumed due to rolling resistance at various rider speeds. You can see that as the rider speed increases, so does the amount of time lost.
Time Lost To Rolling Resistance For 25mm Continental GP 5000 @ 100psi
Time Lost To Rolling Resistance For 25mm Continental GatorSkin @ 100psi
The final table shows the difference between these two tires for various distances at different rider speeds. You can clearly see how important rolling resistance is.
Comparing Time Lost Due To Rolling Resistance for GP 5000 & GatorSkin
How Much Time Wider FLO Rims Save You
For the development of the new FLO All Sport and Gravel Wheel lines we were able to reduce the rolling resistance by widening the internal rim width of our wheels. The widening accounts for a change of 0.0004, which impacts your watts and time savings as shown in the table below. It’s important to note that these times savings are related to Crr alone. The table does not take into account added benefits of aerodynamic optimization.
Time Saved Using FLO All Sport & Gravel Wheels Due To Lower Rolling Resistance
Rolling resistance is incredibly important. The key factors to lowering rolling resistance are wheels, tires, and tire pressure. Our wheels are designed to be optimized for rolling resistance. We’re always happy to recommend tires, and each one of our wheel pages has a tire pressure chart to let you know your optimal tire pressure.
When you are able to optimize each element, the amount of time you save can make the difference between a win and a loss. If you have questions about optimizing your rolling resistance, feel free to reach out—we’ll be happy to offer our advice.