CEMB USA C218 User Manual - Manual (Page 14)

14
Use and maintenance manual Rev. 04-2011
ENGLISH
5.5 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 eccen-
tricity of the wheel down to acceptable limits. The principle
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. alumi-
nium 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)
wheel
rim
tyre
rotation axle
Ideal wheel
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.
SOLUTION: Rotate the tyre on the rim by 180°
RESULT: no improvement is obtained.
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.
Example 3
Rim 0 mm
Tyre + 1.2 mm
Wheel + 1,2 mm
Eccentricity of the wheel cannot be compensated by the
rotation because the rim is perfect!
wheel
rim
tyre
rotation axle
Ideal wheel
Use of the wheel balancer
wheel
rim
tyre
rotation axle
Ideal wheel