I am a design engineer working in a factory manufacturing test-rigs in India. At present, I am developing a dyno for automobile service stations (guarages). The Dyno has rollers, on which the wheels of vehicle rest. An eddy current brake is coupled to the rollers to simulate load on the vehicle. An electronic controller controlling the brake simulates Aerodynamic drag as a function of the speed.
Simulating Aerodynamic drag (described above) is clear to me. However I am not clear about rolling friction. I think weight of the vehicle and the rider (mechanic) will create desired rolling friction load. But some of my colleagues say that we have to simulate rolling friction through the brake, because rotating rollers will not create rolling friction. I am confused. Can anybody guide me on this?
I can push my 5,700# Lincoln Towncar by myself once it starts to move on smooth level ground. Human power is not great horsepower-wise. But if I put my hand out the window at 55 MPH, I can feel considerable force. Multiply the force on the hand times the frontal area of the vehicle, and you can see that rolling force is negligible in comparison. I could be totally mistaken though. Perhaps if you took a spring scale and measured how much force is involved once the car is moving and just add that?
My understanding is that roll is a linear function of vehicle weight and tire RRC (Rolling Resistance Coefficient). I did the math for my 3100 lb (~1400 kg) Subaru and it came out to somewhere in the 3-6 hp range at 60 mph. Rolling a tire on a circular roller instead of a flat road WILL change the RRC, but I doubt it would be significant enough to need a correction, as it's very likely within the measurement resolution of the dyno itself.