Dyno Dynamics: some math

How torque and horsepower are derived from measurements recorded on a Dyno Dynamics:

Calculated torque (Nm) = Tractive Effort (N) * Roller radius (m)
Roller speed (RPM)= (Vehicle speed (km/h) * 1000) / 60 / Roller circumference (m)

Torque at wheels (Nm) = Calculated torque (Nm) / (Engine speed/Roller speed)
Power at wheels (PS) = Torque at wheels (Nm) * Engine speed (RPM) / 7020

Example:
Roller diameter: 0.217m
Roller circumference: 0.681726m
Vehicle speed: 130 km/h
RPM: 5417
Tractive Effort: 7866 N

Calculated torque = 7866 * (0.217/2) = 853.461 Nm
Roller speed = 130 * 1000 / 60 / 0.681726 = 3178.207 RPM
Torque at wheels = 853.461 / (5417/3178.207) = 500.734 Nm
Power at wheels = 500.734 * 5417 / 7020 = 386.4 PS