1. variations in tyre pressure and road surface
Coast-down conditions issues arising from of TUG-TNO correction algorithms project
variations in tyre pressure and road surface

2. Correction algorithms for variations in the WLTP testing
Coast-down conditions
Correction algorithms for variations in the WLTP testing
Correcting of the test results for the execution of the test
variations in test conditions and test parameters
Chassis dynamometer test correction algorithms: (TUG)
State-of-Charge of the battery
deviations of the WLTC velocity trace
total WLTC cycle distance ….
Road load (coast-down) test correction algorithms: (TNO)
rotational inertia of wheels and tyres
ambient conditions (temperature and relative humidity)
…..
preliminary
results

3. Coast-down conditions
Two open issues regarding road-load tests large effects without a simple correction method
large variation seen, but no systematic approach yet:
tyre pressure variations among, and during, the coast-down tests
after preconditioning tyre pressure is higher (~8%)
small pressure drop during low velocity testing
the variation in tyre pressure is large: 15%
 similar magnitude effect on rolling resistance (“f0”)
road-surface effect of rolling resistance
testing at three circuits leave a large systematic effect after corrected for all other effects
up to 24% variation in rolling resistance

4. Coast-down conditions
Tyre pressures varies 15% after pre-conditioning limited control over actual tyre pressure
modelling and correcting for the pressure variation is difficult
due to the many influences and processes involved
 measure pressure during the testing

5. Coast-down conditions
Road surface affects rolling resistance Mean Profile Depth, in combination with tyre profile
variations between different test tracks yield up to 24% measured variation in rolling resistance
track 2:
stones and smooth
track 1:
tarmac and rough

6. Recommendations Correct to standard tyre pressure:
Coast-down conditions
Recommendations
Correct to standard tyre pressure:
e.g., fixed value at set pressure + 8%:
Cold tyre: 2.30 bar, after preconditioning: 2.48 bar (+8%)
if pressure is: 2.40 bar  reduce measured f0 by 3.2%
if pressure is: 2.55 bar  increase measured f0 by 2.8%
Correct for road surface variations (Mean Profile Depth):
Develop a standard test:
e.g. pulling a freely rotating wheel with 350 kg at constant velocity
Apply the Mean Profile Depth (MPD) formula:
e.g.: RRCtest = RRCtyre *MPD [0/00]