CEMB USA C88 (A) - Manual (Page 20)

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s sx x
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d dx x
5 50 0°°
s sx x
g g g g
d dx x
4 4 g g 3 3 g g 1 1 g g 6 6 g g
s sx x
g g g g
d dx x s sx x
g g g g
d dx x s sx x
g g g g
d dx x
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!
►
Initial unbalance
phase shift
Possible approximations
residual static r esidual static residual static
Choice with minimum
static residual
With conventional
wheel balancer
residual static
5.5.4 - Automatic minimization of static unbalance ►
This program is designed to improve the quality of
balancing without any mental effort or loss of time by
the operator. In fact by using the normal commercially
available weights, with pitch of 5 in every 5 g, and by
applying the two counterweights which a conventional
wheel balancer rounds to the nearest value, there could
be a residual static unbalance of up to 4 g. The damage
of such approximation is emphasized by the fact that
static unbalance is cause of most of disturbances on
the vehicle. This new function, resident in the machine,
automatically indicates the optimum entity of the weights
to be applied by approximating them in an “intelligent”
way according to their position in order to minimize
residual static unbalance.
SOLUTION:
Rotate the tyre on the rim by 180° RESULT:
wheel eccentricity 0.3 - 0.4 mm / 0,010” - 0,015”
(in tolerance)
Example 1
Rim + 0.8 mm / 0,030”
Tyre + 0.6 mm / 0,0225”
Wheel + 1.3 mm / 0,05”
Eccentricity of the wheel is
excessive, due to an acceptable
rim or tyre but randomly placed in an
“unfortunate” relative position.
wheel
rim
tyre
rotation axle
Ideal wheel