Rolling Resistance Crr / RRC for specific Tires

[dcb]

second the remove the half shafts suggestion, figure out how to accelerate it (push it with another car and a tire?) and do some coastdowns without the axles. Then put it back together and do coastdowns with the axles and the difference is the transaxle/driveline.

[bwilson4web]

Actually, I had used this as my starting place with:

Evalutaion of 2004 Toyota Prius Hybrid Electric Drive System, R. H. Staunton, C. W. Ayers, L. D. Marlino, J. N. Chiasson, T. A. Burress, May 2006, ORNL/TM-2006/423, UT-Battelle

But roll-down tests would be impractical.

If I do this, I will put the front on jack-stands and some mechanism to keep the tires rotating at the same speed . . . some kind of hillbilly dyno. But I won't be putting 3,000 lbs of rolling, unpowered metal on the street.

Bob Wilson

[Bill in Houston]

For rolling resistance I thought you could push it at a constant speed, and measure the force required, and then another speed, and measure the force required, and get a line from that. So remove the halfshafts, and push it 2 mph (measure the force), and push it 5 mph (measure the force). Even if the short test stretch of has a slope, you can back out the effect of that by using the same stretch each time you test. You use a low speed to keep aero effects out of it. You're smart enough to do big piles of math, but you are also smart enough to know that nothing beats actual data.

[bwilson4web]

Actually I had thought about a 5th wheel or trailer setup to measure tire rolling resistance. I saw a photo where the test tire was on a towed trailer with force sensors. My thinking is the trailer with 4-lug and 5-lug configuration would allow testing of 14", 15" and 17" wheels and hauling the unit to GreenDriveExpo. Then we could survey any tires that anyone wants to 'loan' for testing.

The other thought is to rig up a 4-wheel, multi-zone, IR thermal setup so we could measure temperature distributions across each tire tread, three are all that are needed. Then offer it as a free, dynamic alignment check with EZ-shim or metal tab shims available at cost to support 4-wheel alignment. In the meanwhile, collecting the ratio of tire temperatures to road and air temperatures would give a good, 1st order metric of relative rolling resistance. Same idea as before, offer it at GreenDriveExpo.

I like the second approach because no tire changing is involved which will speed up data collection. Best of all, the owner gets useful information that they can follow-up with if they want to optimize their alignment. Everybody wins.

As for the transaxle testing, I'm really interested in the relative transaxle oil effects and the study cited earlier has loss curves that show an exponential curve. I should be able to use the viscosity formula to make a parametric set to understand what is the likely effect, the magnitude. Then do a couple of point-measurements to apply to the curves and voila, a practical transaxle friction/viscosity loss model.

As for the measurements, I really want to avoid hill rolling in this case as I think I can get better data with known drive and load forces.

Bob Wilson