What are typical values for Free Rolling Drag coefficient?

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brian
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What are typical values for Free Rolling Drag coefficient?

Post by brian »

Q: Anyone aware of any testing for COF for a free rolling vehicle on pavement or grass, wet or dry??
A: See SAE 980368 The measured Rolling Resistance of vehicle for Accident Reconstruction by Cliff & Bowler
The numbers they cite are low but it is another source for consideration. Also, in collisions, one or more of the wheels may be locked or have additional rolling resistance due to collision related damage to the structure and/or drivetrain.
From the paper:
ABSTRACT
  • Knowledge about vehicle rolling resistance is required to calculate speed loss of accident vehicles during portions of their pre-impact and post-impact trajectory when they are not braking or sliding directly sideways. The accuracy of assumed rolling resistance values is most important in accidents with long post-impact roll out distances. Very little hard data are currently available and the accident reconstructionist must usually make estimates of drivetrain losses and normal and damaged tire rolling resistance to determine overall vehicle rolling resistance.
    In the first part of this study, the rolling resistances of various vehicles with different drive configurations are determined, based on accurate measurements made with a 5th wheel. In the second part, sensitivity analyses are done with PC-Crash2, a computer simulation program, to determine what effect the error in assumed rolling resistance has on speed calculations for various types of post-impact trajectories.
CONCLUSIONS
  • 1. Brake factors of 0.007 to 0.015 (of normal load) were obtained at 2 m/s for free-rolling wheels of the vehicles tested. These values increased to the 0.017 to 0.024 range at 12 m/s. This range does not include the Ford Ranger drag because the Ranger's drag was higher in neutral than in fourth gear (overdrive).
    2. Manual transmission vehicle drive wheel brake factors ranged from 0.035 to 0.064 in 5th gear to 0.097 to 0.364 in 1st gear.
    3. Automatic transmission vehicle drive wheel brake factors ranged from 0.034 to 0.082 in 3rd gear to 0.144 to 0.284 in 1st gear, at 12 m/s. However, below the speed at which the torque converter disengaged and the engine stopped rotating these brake factors dropped to values close to those of free rolling wheels.
    4. Flat tire brake factors of 0.12 to 0.21 were obtained.
    5. Accidents involving at least some post-impact spin, and for which measurements of post-impact tire marks have been taken, can often be reconstructed with a trajectory simulation program without detailed knowledge of brake factors.
    6. Accidents involving post-impact rollout only cannot be reconstructed with a trajectory simulation program without detailed knowledge of brake factors, unless vehicle damage is also taken into account.
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Re: What are typical values for Free Rolling Drag coefficient?

Post by MSI »

here's another publication on the topic:
White, K., Merala, R., Desautels, D., and Ellis-Caleo, T., "Rollout Deceleration of Modern Passenger Vehicles," SAE Technical Paper 2012-01-0616, 2012

Abstract:
  • Vehicle post-impact travel distances are often available to the accident reconstructionist. Energy dissipated after impact can be significant, and it is often necessary to account for this energy. The deceleration and energy dissipation experienced by a vehicle after a collision is dependent on many variables including tire rolling resistance, engine and drive-train resistance and aerodynamic drag. New technologies that significantly modify the traditional drive train, low rolling resistance tires, and new aerodynamic body designs affect vehicle deceleration, but associated data is not widely available. Roll-out tests were performed in which speed, acceleration and position measurements were made. Vehicles tested were equipped with hybrid (gasoline-electric) and standard engines, CVT (continuously variable transmission), manual and automatic transmissions, and two wheel and four-wheel drive. Results are presented to characterize the effect of vehicle speed, gear, and ignition status (engine on or off). The different measurement methodologies employed are compared for accuracy, repeatability and ease of use. A review of published vehicle decelerations is presented and compared to the data collected in the current series of tests. The applicability of this new deceleration data to a range of vehicles similar to those tested is discussed.
CONCLUSIONS
  • 1. The average rolling deceleration of the vehicles tested in neutral was 0.018 g.
    2. The average rolling deceleration of the vehicles tested with the engine off was 0.018 g.
    3. The average rolling deceleration of the standard automatic transmission vehicles tested in drive decreased with decreasing speed from an average of 0.035 g at 30 mph to 0.011 g just prior to rest (with an overall average of 0.028 g).
    4. The rolling decelerations of the hybrid Honda Civics were similar in neutral and with the engine off, but the hybrid experienced greater deceleration in drive.
    5. The rolling deceleration in drive, of the Nissan Altima with continuously variable transmission, was significantly higher than the tested vehicles with automatic transmissions.
    6. The rolling deceleration of the all wheel drive and two wheel drive Toyota Sienna minivans were similar in drive, neutral and with the engine off, but different in the lower gears.
    7. Vehicle rolling deceleration was higher in lower gears, decreased rapidly with decreasing speed, and differed by vehicle.
    8. The results found in this study may be of use in accident reconstruction applications for these or similar vehicles.
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Re: What are typical values for Free Rolling Drag coefficient?

Post by MSI »

June 13, 2012: Please see topic Rolling Resistance of Vehicle in Park and various gears for additional information
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Re: What are typical values for Free Rolling Drag coefficient?

Post by MSI »

June 14, 2012: Came across a couple of references on rolling resistance of pneumatic tires:

NHTSA Tire Fuel Efficiency Consumer Information Program Development: Phase 2 – Effects of Tire Rolling Resistance Levels on Traction, Treadwear, and Vehicle Fuel Economy
August 2009
  • This report summarizes the second phase of the project to develop a tire fuel efficiency consumer information program intended to examine possible correlations between tire rolling resistance levels and service variables such as vehicle fuel economy, wet and dry traction, and outdoor and indoor treadwear. Tires of 15 different models with known rolling resistances were installed on the same new passenger car to evaluate their effects of on vehicle fuel economy. A 10percent decrease in tire rolling resistance resulted in an approximately 1.1-percent increase in fuel economy for the vehicle. This result was within the range predicted by technical literature. Reducing the inflation pressure by 25 percent resulted in a small but statistically significant decrease of approximately 0.3 to 0.5 miles per gallon for four of the five fuel economy cycles, excluding the high-speed, high-acceleration US06 cycle. This value was smaller than many values predicted by technical literature, and possible explanations are being explored.
    Tires of 16 different models with known rolling resistances were subjected to dry and wet skid-trailer testing on asphalt and concrete skid pads. Both the peak (maximum) and slide (fully locked-tire) coefficients of friction were measured and indexed against the control tire. For the tires studied, there appeared to be no significant relationship between dry peak or slide numbers and rolling resistance. However, these tire models exhibited a strong and significant relationship between better rolling resistance and poorer wet slide numbers. The peak wet slide number displayed the same tendency, but the relationship was much weaker. This may be significant to consumers without anti-lock braking systems (ABS) on their vehicles since the wet slide value relates most closely to locked-wheel emergency stops. For newer vehicles with ABS or electronic stability control systems, which operate in the earlier and higher wet peak friction range, the tradeoff is less significant. For the subset of 5 tire models subjected to on-vehicle treadwear testing (UTQGS), no clear relationship was exhibited between tread wear rate and rolling resistance levels. For the subset of 6 tire models subjected to significant amounts of wear in the indoor treadwear tests, there was a trend toward faster wear for tires with lower rolling resistance. This report concludes with an analysis of the various options in the draft ISO 28580 rolling resistance test and their likelihood of inducing variability in the test results, as well as a discussion of data reporting format.
CONCLUSIONS
  • Based on five different fuel economy cycles, a 10 percent decrease in tire rolling resistance resulted in approximately 1.1 percent increase in fuel economy for the vehicle. This result was within the range predicted by technical literature. Reducing the inflation pressure by 25 percent resulted in a small but statistically significant decrease of approximately 0.3 to 0.5 miles per gallon for four of the five fuel economy cycles, excluding the high-speed, high-acceleration US06 cycle. This value was smaller than many values predicted by technical literature, and possible explanations are being explored.
    For the tires studied, there appeared to be no significant relationship between dry peak or slide numbers and rolling resistance. However, these tire models exhibited a strong and significant relationship between better rolling resistance and poorer wet slide numbers. The peak wet slide number displayed the same tendency, but the relationship was much weaker. This may be significant to consumers without anti-lock braking systems (ABS) on their vehicles since the wet slide value relates most closely to locked-wheel emergency stops. For newer vehicles with ABS or electronic stability control systems, which operate in the lower slip and higher range of wet
    peak friction, the tradeoff is expected to be less significant.
    For the subset of five tire models subjected to on-vehicle treadwear testing (UTQGS), no clear relationship was exhibited between tread wear rate and rolling resistance levels. For the subset of six tire models subjected to significant amounts of wear in the indoor treadwear tests, there was a trend toward faster wear for tires with lower rolling resistance.
A HANDBOOK FOR THE ROLLING RESISTANCE OF PNEUMATIC TIRES
Clark, S.K., Dodge, R.N. ~.
INDUSTRIAL DEVELOPMENT DIVISION, INSTITUTE OF SCIENCE AND TECHNOLOGY, THE UNIVERSITY OF' MICHIGAN ANN ARBOR 1979
PREFACE
  • This handbook is a reprint of a document prepared for the U.S. Department of Transportation, Transportation Systems Center, Cambridge, Massachusetts. Its purpose is to describe the, mechanics of tire rolling loss sufficiently so that those interested in understanding fuel consumption in vehicles may make comparative assessments of potential tires for given vehicle weights, tire inflation pressures, and tire construction features.
    Since tire construction 'details are subject to change, it should be understood that the data given here are probably more valuable in indicating trends than in giving exact numerical values for the rolling resistance of current production tires.
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Re: What are typical values for Free Rolling Drag coefficient?

Post by MSI »

Saw another article referenced on the INCR news forum.
Join NAPARS and have access to all the ARJ issues.

July/Aug 2016 ARJ page 31, PASSENGER CAR COASTDOWN RATES,
By Wade Bartlett, Bill Wright, and Andy Rich
Has some full scale tests, presentations of other test data and the following abstract & Conclusions:
coastdown paper abstract.png
coastdown paper abstract.png (93.77 KiB) Viewed 94 times
coastdown paper conclusions.png
coastdown paper conclusions.png (349.73 KiB) Viewed 94 times
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