Commission Delegated Regulation (EU) 2015/68Show full title

1. Method of measurement for tractors

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 braked.

1.1.2. The brakes shall be applied only on 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 braking 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 (z_max). During each test, a constant input force shall be maintained and the braking rate shall be determined by reference to the time (t) taken for the speed to reduce from 40 km/h to 20 km/h using the formula:

z_max is the maximum value of z in m/s²,

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 t_min, then select three values of t comprised within t_min and 1,05 t_min and calculate their arithmetical mean value tm, then calculate

If it is demonstrated that for practical reasons the three values determined above cannot be obtained, then the minimum time t_min may be utilised. However, the requirements of point 1.3 still apply.

1.1.4. The braking forces shall be calculated from the measured braking rate and the rolling resistance of the un-braked axle(s) which is equal to 0,015 and 0,010 of the static axle load for a driven axle and a non-driven axle, respectively.

1.1.5. The dynamic load on the axle shall be calculated from the braking rate, static axle load, wheelbase and centre of gravity height.

1.1.6. The value of k shall be rounded to three decimal places.

1.1.7. Then, the test shall be repeated for the other axles(s) as defined in points 1.1.1 to 1.1.6 (for exemptions, see points 1.4 and 1.5).

1.1.8. For example, in the case of a two-axle rear-wheel drive vehicle, with the front axle being braked, the coefficient of adhesion (k) is given by:

1.1.9. One coefficient shall be determined for the front axle k_f and one for the rear axle k_r.

1.2. Determination of the adhesion utilised (ε)

1.2.1. The adhesion utilised (ε) is defined as the quotient of the maximum braking rate with the anti-lock braking system operative (z_AL) and the coefficient of adhesion k_M, i.e.

1.2.2. From an initial vehicle speed of 55 km/h, or v_max whichever is lower, the maximum value for the braking rate (z_AL) shall be measured with full cycling of the anti-lock braking system. This value for z_AL shall be based on the average value of three tests, as previously described in point 1.1.3, using the time taken for the speed to reduce from 45 km/h to 15 km/h, according to the following formula:

1.2.3. The coefficient of adhesion k_M shall be determined by weighting with the dynamic axle loads:

Where:

1.2.4. The value of ε shall be rounded to two decimal places.

1.2.5. In the case of a vehicle equipped with an anti-lock braking system of category 1 or 2, the value of z_AL is based on the whole vehicle, with the anti-lock braking system in operation, and the adhesion utilised (ε) shall be given by the same formula quoted in point 1.2.1.

1.2.6. In the case of a vehicle equipped with an anti-lock braking system of category 3, the value of z_AL shall be measured on each axle which has at least one directly controlled wheel.

Example: for a two-axle vehicle with an anti-lock braking system acting only on the rear axle (2), the adhesion utilised (ε) is given by:

This calculation shall be made for each axle having at least one directly controlled wheel.

1.3. If ε > 1,00, the measurements of coefficients of adhesion shall be repeated. A tolerance of 10 % is acceptable.

1.4. For tractors equipped with three axles, any axles that are interconnected by either suspension components and thereby react to weight transfer under braking or driveline may be disregarded in establishing a k value for the vehicle.

Until a uniform test procedure is agreed, vehicles with more than three axles and special vehicles shall be subject to consultation with the technical service.

1.5. For tractors with a wheel base less than 3,80 m and with h/E > 0,25, the determination of the coefficient of adhesion for the rear axle shall be omitted

1.5.1. In that case, the adhesion utilised (ε) is defined as the quotient of the maximum braking rate with the anti-lock braking system operative (z_AL) and the coefficient of adhesion (k_f), i. e.