CEMB USA C218 (A) User Manual

Page 18

I 0568 - 18

5.6 - Eccentricity measurement (ems optional)

The much enlarged ﬁ gures show the outer tyre surface and axis of wheel rotation.

Fig. A shows measurement of the total Peak-to-Peak
eccentricity deﬁ ned as maximum radial deviation of the
tyre surface.

Fig. B shows measurement of the eccentricity of the 1st
harmonic, i.e. the eccentricity of that circle which “reco-
pies” the tyre shape, by averaging the local deviations
of the tyre from the round shape.

Obviously the P.P. measurement is normally greater than that of the 1st harmonic. Tyre manufacturers normally
supply two different tolerances for the two eccentricities.

At the end of the balancing spin it is possible to automatically measure the eccentricity of the tyre through the
SONAR sensor installed on the guard. The sensor should be positioned by hand in front of the tyre tread.

GRAPH 1 : represents the actual Peal-to-Peak eccentricity.
GRAPH 2 : represents the eccentricity of the 1st harmonic. For a wheel to be in optimum conditions, such graph
should approach a straight line.
When the wheel is moved, the on-screen cursor indicates the current value re-phased on the basis of the angle set at
para.

CONTROL OF ECCENTRICITY MEASUREMENT

GRAPH 1 - (red)

GRAPH 2 - (yellow)