In summary, the component of wheel resistance resulting from the tyre is the sum of flexion resistance , frictional resistance , and fan resistance . This sum is also called Rolling Resistance.
FRroll = FRflex + FRfrict + FRfan

This forms a useful summary because in practice the single components of flexing and frictional resistance cannot be separated.
As a result of a nearly linear characteristic of the rolling resistance force over the wheel load, an index relative to the load can be defined, the dimensionless co-efficient of rolling resistance :