CEMB USA C73 (A) - Manual (Page 20)

I 0567 - 20 GB
5.6 - When and why matching
The software associated with eccentricity measurement is a powerful tool for determining the need to perform relative
rotation between the rim and tyre in order to reduce the eccentricity of the wheel down to acceptable limits. The prin-
ciple adopted is based on the consideration that a rim with acceptable tolerance, mounted with an acceptable tyre,
can statistically generate a total eccentricity which is not acceptable but can be improved by matching.
Generally speaking, rim measurement is not necessary, accurate or useful because:
• To measure the rim it is necessary to remove the tyre. There can by coarse errors on the outside (e.g. aluminium
wheels!)
• The two rim sides can be eccentric in a very different way. Therefore to which one to make reference? What is the
effect on the tyre mounted?
• To improve the eccentricity of a wheel, the rim should be eccentric, to compensate the tyre. And viceversa.
• If after a rotation by 180° of a wheel, the value is still out-of-tolerance, either the tyre or rim are too eccentric: One
of the two must be replaced!
►
SOLUTION:
Rotate the tyre on the rim by 180°
RESULT:
wheel eccentricity 0.3 - 0.4 mm (in tolerance)
Example 1
Rim + 0.8 mm
Tyre + 0.6 mm
Wheel + 1.3 mm
Eccentricity of the wheel is
excessive, due to an acceptable
rim or tyre but randomly placed in an
“unfortunate” relative position.
Example 2
Rim + 0.8 mm
Tyre - 0.6 mm
Wheel + 0.3 mm
Eccentricity of the single items has
been compensated.
The wheel is acceptable.
wheel
rim
tyre
rotation axle
Ideal wheel
wheel
rim
tyre
rotation axle
Ideal wheel