Document ID: chunk:federal_register_of_legislation:F2021C00477:body:0:p52
Version: federal_register_of_legislation:F2021C00477
Segment Type: other
Provision Reference: 
Character Range: 136902–140065

(9.81 m/s2)

h                                height of centre of gravity specified by the manufacturer and agreed by the Technical Service conducting the approval test

k                                coefficient of adhesion between tyre and road

kf                               k - factor of one front axle

kH                               k - value determined on the high-adhesion surface

ki                               k - value determined on axle i for a vehicle with a category 3 anti-lock system

kL                               k - value determined on the low-adhesion surface

klock                            value of adhesion for 100 per cent slip

kM                               k - factor of the power-driven vehicle

kpeak                            maximum value of the curve "adhesion versus slip"

kr                               k - factor of one rear axle

P                                mass of individual vehicle (kg)

R                                ratio of kpeak to klock

t                                time interval (s)

tm                               mean value of  t

tmin                             minimum value of  t

z                                braking rate

zAL                              braking rate z of the vehicle with the anti-lock system operative

zm                               mean braking rate

zmax                             maximum value of  z

zMALS                            zAL of the power-driven vehicle on a "split surface"

Annex 6

Appendix 2

Utilization of adhesion
1. Method of measurement
1.1. Determination of the coefficient of adhesion (k)
1.1.1. The coefficient of adhesion (k) shall be determined as the quotient of the maximum braking forces without locking the wheels and the corresponding dynamic load on the axle being brakes.
1.1.2. The brakes shall be applied on only one axle of the vehicle under test, at an initial speed of 50 km/h. The braking forces shall be distributed between the wheels of the axle to reach maximum performance. The anti-lock system shall be disconnected, or inoperative, between 40 km/h and 20 km/h.
1.1.3. A number of tests at increments of line pressure shall be carried out to determine the maximum braking rate of the vehicle (zmax). During each test, a constant input force shall be maintained and the braking rate will be determined by reference to the time taken (t) for the speed to reduce from 40 km/h to 20 km/h using the formula:
 zmax is the maximum value of z; t is in seconds.
1.1.3.1. Wheel lock may occur below 20 km/h.
1.1.3.2. Starting from the minimum measured value of t, called tmin , then select three values of t comprised within tmin and 1.05 tmin and calculate their arithmetical mean value tm ,
then calculate:
 If it is demonstrated that for practical reasons the three values defined above cannot be obtained, then the minimum time tmin may be utilized. However, the requirements of paragraph 1.3. shall still apply.
1.1.4. The braking forces shall be calculated from the measured braking rate and the rolling resistance of the unbraked axle which is equal to 0.015 and 0.010 of the static axle load for