Rolling friction of the vehicle.

[sankapal]

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?

Regards,
Sankapal

Regards,
Sankapal

[flapdoodle]

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?

[samandw]

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.

[samandw]

Found this excellent resource:
http://en.wikipedia.org/wiki/Rolling_resistance

[DRW]

Change the diameter of the rollers to adjust rolling resistance. Smaller rollers have more resistance.

Here's some technical info, although it was done for bicycle exercise equipment and lower power levels.
>Kreitler rollers
Address:http://www.kreitler.com/wattage.php?section=wattage

[bowtieguy]

my father-in-law once told me a story about a synthetic lube salesman...

he said the guy offered to pay for a full powertrain fluid exchange(from dino to his synthetic, stem to stern) for a tractor trailor. he would set up a test...

drive the truck(w/ stock dino oils) to 55mph, then shut the truck off, and finally measure the distance to a stop. next, do the same AFTER changing all the fluids to his synthetics.

he offered to switch the fluids back if the truck didn't roll a greater distance w/ his products.

i don't remember the brand and nor the results, unfortunately!