GB/T 18505-2013Dynamic balance test method for motor vehicle tyres (English PDF)

3.1 Unbalance

Static unbalance, dynamic unbalance, or both.

3.2 Static unbalance value

The product of the tyre's mass and the center of mass eccentricity, expressed in g - cm.

NOTE: when the tyre rotates at a certain speed, the static unbalance generates a centrifugal force perpendicular to the axis of rotation, which can be expressed by Formula (1). Where, Fs---the unbalanced centrifugal force, expressed in (N);

M---the tyre mass, expressed in (g); e---the center of mass eccentricity, expressed in (cm); pi---Pi; n---the rotational speed, expressed in (r/min).

NOTE: since the tyre deforms under centrifugal force, the center of gravity eccentricity can be used as a function of rotational speed.

3.3 Static unbalance mass

The static unbalance value divided by the compensating radius, expressed in (g).

NOTE: the static unbalance mass can be expressed by Formula (2). Where, ms---the static unbalance mass, expressed in (g);

R---the compensating radius, expressed in (cm); m---the tyre mass, expressed in (g); e---the center of mass eccentricity, expressed in (cm);

3.4 Dynamic unbalance value

This can be expressed as the couple moment unbalance value, which is the product of axial inertia minus radial inertia and then multiplied by the sine of the included angle between the tyre's principal axis of inertia and its axis of rotation. The unit is g - cm².

NOTE 1: when the tyre rotates at a constant speed, the dynamic unbalance generates a bending moment perpendicular to the axis of rotation, which can be expressed by Formula (3).

Where, sinalpha---when alpha is very small and expressed in radians, sinalpha ~ alpha; M---the unbalanced torque, expressed in (N - m); Ia---the axial inertia, expressed in (g - cm²); Id---the radial inertia, expressed in (g - cm²);

alpha---the included angle between the principal axis of inertia and the wheel axle centerline, expressed in (°); n---the rotational speed, expressed in (r/min); pi---Pi.

NOTE 2: since the tyre deforms under centrifugal force, the axial inertia and radial inertia can be used as functions of rotational speed.

3.5 Couple unbalance value

Dynamic unbalance value divided by the distance between compensating side, expressed in (g - cm).

3.6 Couple unbalance mass of each side

Couple unbalance value divided by the compensating radius, expressed in (g).

3.7 Compensating side

Two symmetrical rotating planes on either side of the tyre used for balancing the counterweight (on a horizontal tyre, they can be divided into an upper compensating side and a lower compensating side).

3.8 Distance between compensating side

The distance between two compensating sides.

NOTE: the distance between compensating side can be expressed by Formula (4). Where, W---the distance between compensating side, expressed in (cm); C---the measured width of the rim, expressed in (cm);

B---the measured width of the rim flange, expressed in (cm). For specific data, refer to GB/T 3487 (if the value specified in the Standard is not a fixed value but a minimum value, the minimum value shall be used).

3.9 Compensating radius

The distance from the center of the tyre's counterweight to the wheel axle centerline.

NOTE: the compensating radius can be expressed by Formula (5). Where, R---the compensating radius, expressed in (cm); D---the nominal diameter code of the rim;

G---the standard rim flange height, expressed in (cm). Specific values are given in GB/T 3487.

3.10 Compensating side unbalance mass

The composite mass of the static unbalance mass (static unbalance value divided by the compensating radius) and the couple unbalance mass (couple unbalance value divided by the compensating radius) on the same compensating side, obtained in accordance with the parallelogram law of vector addition. It is expressed in (g).

NOTE: the composition of compensating side unbalance mass is shown in Figure 1. Use Formula (6) to calculate the upper compensating side unbalance mass, and Formula (7) to calculate the lower compensating side unbalance mass. […]