GB/T 34378-2017Dynamic balance test method for motorcycle tyres (English PDF)

3.1 Static unbalance value

Product of the tyre mass multiplied by the center of gravity eccentricity.

Note 1: When the tyre rotates at a certain speed, the static unbalance produces a force perpendicular to the axle. Calculate the static unbalance value according to Formula (1):

Where:

Sin alpha -- when alpha is small enough to be expressed in radians, sin alpha ~ alpha; M -- unbalanced moment, in newton meters (N·m); Ia -- axial inertia, in gram square centimeter (g·cm2); Id -- radial inertia, in gram square centimeter (g·cm2);

alpha -- the angle between the main inertia axis and the axle centerline, in degrees (°); n -- rotating speed, in revolutions per minute (r/min); pi -- Pi.

Note 3: Since the tyre is deformed under the action of rotation, the axial inertia and the radial inertia can be used as the function of the rotating speed.

3.4 Couple unbalance value

Dynamic unbalance value divided by the distance between compensating sides.

Note: The unit is expressed in g·cm.

3.5 Couple unbalance mass of each side

Couple unbalance value divided by the compensating radius.

Note: The unit is expressed in g.

3.6 Compensating side

Two rotation planes symmetrical on both sides of the tyre for balance weight (for the tyre in a horizontal attitude, it can be divided into an upper compensating side and a lower compensating side).

3.7 Distance between compensating side

Distance between two compensating sides.

Note: The distance between compensating sides is expressed by Formula (4): Us -- static unbalance value, in gram centimeter (g·cm); Uc -- couple unbalance value, in gram centimeter (g·cm);

gamma s -- heavy point positioning angle of static unbalance, in degrees (°);

gamma c -- heavy point positioning angle of couple unbalance, in degrees (°); R -- compensating radius, in centimeters (cm).

3.10 Heavy point positioning angle

The circumferential angle BETWEEN the heavy point which produces unbalance AND the specified reference point.

Note: Formula (8) and Formula (9) can be used respectively to calculate the heavy point positioning angle of the upper compensating side AND the heavy point positioning angle of the lower compensating side.

Where:

gamma u -- heavy point positioning angle of the upper compensating side, in degrees (°);

gamma l -- heavy point positioning angle of the lower compensating side, in degrees (°);

The interpretation of other symbols is the same as in Formula (6) and Formula (7).

In Formula (8) and Formula (9), the superposition of the two angles is calculated by such method -- the heavy point positioning angle of the couple unbalance value is taken as the starting point; addition is used for those of clockwise direction; and subtraction is used for those of counter-clockwise direction.

5.4 Test pressure

The test pressure of the motorcycle tyre is 250 kPa, and the allowable deviation of the test pressure shall be within ±50 kPa.

6.1 Set tyre unbalance compensating radius and distance between

compensating side for the test machine.