Cyclists know that their energy is valuable and needs to be used with scarcity. But all the energy a cyclist put on the pedals does not end-up equally.

Weight is a thine enemy… in climbs.

A typical rider will spend most of its energy (85%) to lift him up in mountains. The remaining part (~15%) dissipates in frictions. Because of this, weight has always been a major concern for most cyclists.

Energy loss split in a steep climb (7%)

Frictions account for 100% of power losses on flat roads

But the story is radically different when it comes to flat roads. In this case gravity do not play any role. 100% of the energy is lost in frictions (more than 90% through aerodynamic friction losses and 10% through rolling friction losses).

Energy loss split in a flat road

When we look closely we can see that the transition between gravity and friction as a function of slope is not blunt, but rather smooth. Even with a 4% grade road, 1/3 of the energy is lost in friction!

Energy consumption split as a function of road slope.

Two magic parameters : CdA & Crr

The frictions can be summarized with two coefficient, which are utmost important to know : CdA (Coefficient of Drag) & Crr (Coefficient of rolling resistance). Those parameters determine the amplitude of respectively aero & rolling frictions forces. They are just simply as important as weight.

To summarize :
Weight : parameter determining the gravity force amplitude
CdA : parameter determining the aero friction force amplitude
Crr: parameter determining the rolling friction force amplitude

Knowing precisely these 3 parameters on top of the capability to produce power (FTP) directly determines the speed of the rider.

Example of the calculation of a rider speed based on the 4 key parameters FTP, Crr, CdA & weight.

Now if you have read this page carefully one concern should immediate pop-up in you mind : “how do I assess frictions?”. Well… hum let’s have a look at Aeroscale capability!