CEMB USA C88 EVO (C) - Manual (Page 17)

17
Use and maintenance manual Rev. 02-2010
ENGLISH
5.10 ECCENTRICITY MEASUREMENT
5.10.1 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!
Use of the wheel balancer
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.
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.
SOLUTION: Rotate the tyre on the rim by 180°
RESULT: wheel eccentricity 0.3 - 0.4 mm (in tolerance)
SOLUTION: Rotate the tyre on the rim by 180°
RESULT: no improvement is obtained.
Example 3
Rim 0 mm
Tyre + 1.2 mm / 0,045”
Wheel + 1,2 mm / 0,045”
Eccentricity of the wheel cannot be
compensated by the rotation because
the rim is perfect!
wheel
rim
tyre
rotation axle
Ideal wheel
wheel
rim
tyre
rotation axle
Ideal wheel