Division 4.1.7.2 Principle of the approachF1

The principle is the use of a control tyre set and two different instrumented passenger cars for the test cycle of a candidate tyre set in comparison with a reference tyre set.

One instrumented passenger car is fitted with the reference tyre set followed by the control tyre set, the other with the control tyre set followed by the candidate tyre set.

The specifications listed in sections 4.1.2 to 4.1.4 apply.

The first test cycle is a comparison between the control tyre set and the reference tyre set.

The second test cycle is a comparison between the candidate tyre set and the control tyre set. It is done on the same test track and during the same day as the first test cycle. The wetted surface temperature shall be within ± 5 °C of the temperature of the first test cycle. The same control tyre set shall be used for the first and the second test cycles.

The wet grip index of the candidate tyre ( G(T)) is calculated as follows:

G(T) = G ₁ × G ₂

where:

• G ₁ is the relative wet grip index of the control tyre (C) compared to the reference tyre (R) calculated as follows:

  $G_1=\left[\frac{\mathrm{BFC(C)}}{\mathrm{BFC(R)}}\times 125+a\times \left(t-t_0\right)+b\times \left(\frac{\mathrm{BFC(R)}}{{\mathrm{BFC(R}}_0)}-\mathrm{1,0}\right)\right]\times {10}^{-2}$

• G ₂ is the relative wet grip index of the candidate tyre (T) compared to the control tyre (C) calculated as follows:

  $G_2=\frac{\mathrm{BFC(T)}}{\mathrm{BFC(C)}}$