Wang X. Vehicle Noise and Vibration Refinement

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Vehicle noise and vibration strategy-based diagnostics 395

is always advisable to reduce run-out as far as possible in order to obtain

optimum results under all conditions.

Figure 16.7 shows lateral and radial run-out measurement locations for

steel and alloy wheels.

16.2.6 Fitting new tyres

When ﬁ tting a new tyre to a wheel, it is important to ensure that the tyre

is correctly indexed to the wheel, i.e. the ﬁ rst harmonic high point of the

tyre should be ﬁ tted so that it is matching the ﬁ rst harmonic low point of

the wheel. The matching minimizes the effects of force variation inherent

in tyre manufacture.

All wheels have a mark on the outer ﬂ ange indicating the ﬁ rst harmonic

low point (a drill point), a paint mark or an ‘O’. Australian manufactured

tyres have a red dot on the sidewall indicating the ﬁ rst harmonic high point.

European manufactured tyres have a white dot on the sidewall indicating

the ﬁ rst harmonic low point. Some Japanese manufactured tyres have a red

dot on the sidewall indicating the ﬁ rst harmonic high point and a yellow

dot indicating a static balance point.

Lateral run-out Radial run-out

Steel wheel Alloy wheel

A: Lateral run-out

B: Radial run-out

16.6 Lateral and radial run-out.

16.7 Steel and alloy wheel run-out.

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396 Vehicle noise and vibration reﬁ nement

16.3 Balancing

The purpose of wheel balancing is to undo the wheel vibrations, or at least

to reduce them to an acceptable limit, thus avoiding all consequent troubles

and damage such as:

• Tyre wear

• Early bearing wear

• Damage to shock absorbers and other steering parts

• Loosening of the vehicle body and screw bolts

• Detachment or peeling of electric wires

• Difﬁ cult drive and lower road control due to wheel tripping and shimmy

effects

• Reduced comfort for passengers.

Wheel balancing is achieved by applying some masses with suitable weights

on the wheel in such a way as to avoid vibration.

The centrifugal force is due to the unbalance mass. If p is the unbalance

weight and its mass is given by m = p/g (g = acceleration due to gravity),

the centrifugal force is then:

Frm r

ωω

(16.1)

where ω is angular speed. If p = 50 g, in a wheel having an outer diameter

D = 600 mm and running at V = 120 km/h, the weight generates a centrifu-

gal force:

63 6

50 120

63 6 600

18 9

.kg

(16.2)

Also, a little centre error e (mm) on a wheel having a weight P (kg) gener-

ates an unbalance

2000

(16.3)

If a wheel has a weight P of 20 kg, a centre error e of 0.3 mm would cause

an unbalance of

p =

××

2000 20 0 3

600

grams

and a centrifugal force of

F =

20 120

63 6 600

.kg

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Vehicle noise and vibration strategy-based diagnostics 397

16.3.1 Wheel balancing methods

Two balancing methods are available:

• Wheel balancing separately, off the vehicle, by means of suitable balanc-

ing machines

• Wheel balancing on the vehicle by means of suitable units.

These two methods differ either because of their different peculiarities of

use or because they involve different results from a technical viewpoint,

owing to their different limits and possibilities.

Wheel balancing is necessary in the following circumstances:

• When each tyre is changed

• After about 20,000 km running either in the case of a new vehicle or in

the case of a new tyre

• For a sports car, after 5000 km and every 10,000 km

• When a tyre is reﬁ tted after repair or every time vibration or shimmy

effects are noted

• On the spare wheel.

16.3.2 Static and dynamic balance

There are two types of tyre/wheel balance – static and dynamic:

• Static balance affects the distribution of weight around the wheel

circumference.

• Dynamic balance affects the distribution of weight on each side of the

lateral tyre/wheel datum plane.

As a rule, vehicles are more sensitive to static imbalance than to dynamic

imbalance, with as little as 5 grams capable of inducing a vibration in some

models. Vibration induced by static imbalance will cause a vertical or

‘bouncing’ motion of the tyre. Static imbalance is shown in Fig. 16.8, and

the vibration patterns in a wheel due to a static imbalance are shown in Fig.

16.9 where the effects of the static imbalance are vertical rebound, surging,

shimmy and wear.

Shaft

axis

(a) (b)

Inertia

axis

16.8 Static imbalance.

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16.9 Vibration patterns due to static imbalance.

Shaft axis

Axis of inertia

16.10 Dynamic imbalance.

16.11 Shimmy, caused by dynamic imbalance.

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Vehicle noise and vibration strategy-based diagnostics 399

(a)

(b)

Direction of movement

Direction of movement Direction of movement

Balance

weight

Balance

weight

Heavy

spot

Heavy

spot

Direction of movement

Balance

weight

Direction of movement

16.12 The difference between (a) static balance and (b) dynamic

balance.

Dynamic imbalance is shown in Fig. 16.10. It results in a side-to-side

motion of the tyre sometimes referred to as shimmy, as shown in Fig. 16.11.

The difference between static and dynamic wheel balance is shown in Fig.

16.12.

All four tyre/wheel assemblies should be balanced as close to zero as

possible, carefully following the wheel balancer manufacturer’s instruction

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400 Vehicle noise and vibration reﬁ nement

for proper mounting techniques to be used on different types of wheels.

The standard balancing tolerance rates, valid for each wheel side, are indi-

cated in Table 16.1.

For special cases, the balancing tolerance can be determined by the fol-

lowing formula:

G= 367.

(16.4)

where:

p = balancing tolerance (g)

P = wheel weight (kg)

D = wheel outer diameter (road contact) (mm)

d = diameter where counterweights can be put (rim diameter) (mm)

v = maximum vehicle speed (km/h)

G = balancing grade (see Table 16.1).

For standard cars, the ratio D/d is about 1.3 and the balancing tolerance

can be determined from Fig. 16.13 as a function of the car’s top speed on

the road and the wheel weight.

Once all four tyre/wheel assemblies have been corrected for run-out and

imbalance, reinstall them on the vehicle and double check the on-vehicle

run-out. It must remain within tolerance. Evaluate the vehicle at the speed

to which the complaint related and note if the vibration has been corrected.

In most cases, the above procedures will reduce the vibration to an accept-

able level, especially if the run-out has been reduced to an absolute

minimum.

If the vibration is still present, or is reduced but still unacceptable, one

of two possibilities exists:

• For on-vehicle imbalance, the imbalance may result from the compo-

nents other than the tyre/wheel assemblies such as hubs, rotors, etc.,

having imbalance.

• Radial or lateral force variation.

Table 16.1 Standard wheel balancing tolerance rates

Balancing grade (G) Vehicle types Tolerance (grams)

12 Fast cars and motorcycles 5

14 Standard cars and motorcycles 10

16 Light motor lorries 30

18 Standard motor lorries 60

20 Heavy trucks 150

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Vehicle noise and vibration strategy-based diagnostics 401

16.3.3 Vehicle wheel balancing

Wheel unbalances can always be traced back to a static unbalance m

and

couple unbalances m

and m

as shown in Fig. 16.14.

Wheel balancing is an operation by which some masses are applied on

the two wheel sides. Due to the fact that the planes in which to apply bal-

ancing masses are the same as those in which m

and m

are lying, it is

necessary to split m

into masses m

and m

lying on such planes as shown

in Fig. 16.15. By adding m

and m

on the left plane S and m

and m

the right plane D, two masses m

and m

are obtained. The balancing of the

wheel is then achieved by applying two masses having the same values as

and m

but diametrically opposed to m

and m

on the two wheel sides.

P = 10 kg

50 60 70

Balancing tolerance (grams)

80 90 100

Speed (km/h)

120 140 160 180 200

16.13 Balancing tolerance.

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402 Vehicle noise and vibration reﬁ nement

Unbalanced corrections are made by applying counterweights in hard lead

alloy which are ﬁ xed to the rims by means of a steel spring or are

self-adhesive.

Tyre/wheel assemblies can be balanced off the vehicle or on the vehicle.

On-vehicle balancing is the best choice as the balance is not affected when

the tyres are rotated. Also, on-vehicle balances are generally more accurate

than off-vehicle balances (as shown in Fig. 16.16) and can perform dynamic

as well as static balance.

16.14 Couple unbalance.

Plane S Plane D

16.15 Plane S and plane D.

16.16 Off-vehicle wheel balancer.

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Vehicle noise and vibration strategy-based diagnostics 403

Deposits of foreign material must be cleaned from the inside of the

wheel. Stones should be removed from the tread in order to avoid operator

injury and to obtain a good balance. The tyre should be inspected for any

damage, then balanced according to the equipment manufacturer’s instruc-

tions. Always use coated weights on aluminium wheels to prevent cosmetic

damage to the wheel ﬁ nish. Figure 16.17 shows various types of weights,

and Fig. 16.18 shows a weight applied to a wheel in a balancing machine.

Wheel balancers can drift out of calibration, or can be inaccurate as a

result of abuse. This can happen without any visual clue that a problem

exists. Even though the equipment indicates that an assembly is balanced,

an imbalance may still be present. A quick calibration check can be made

using the following procedure:

1. Spin the balancer without a wheel, or any of the adaptors on the shaft.

The readings should be 0 ± 5 grams.

2. Next balance a tyre/wheel assembly that is within radial and lateral

run-out tolerances to ‘zero’, using the balancer.

3. Add a 50 gram test weight to the wheel at any location and re-spin the

assembly. The balancer should call for 50 grams of weight, 180° opposite

the test weight, in the static and dynamic modes. In the dynamic mode,

the weight should be called for on the ﬂ ange of the wheel opposite the

test weight.

16.17 Various types of counterweights for vehicles.

Adhesive

wheel weight

placements

Wheel

weight

placements

16.18 Balancing counterweight applied on a wheel ﬁ tted in a

balancing machine.

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404 Vehicle noise and vibration reﬁ nement

4. With assembly imbalance to 50 grams, cycle the balancer ﬁ ves times.

The balance readings should not vary by more than 5 grams.

5. Index the wheel assembly at four separate locations on the balancer

shaft, 90° apart. Cycle the balancer with the assembly at each location

and record the results. The readings should not vary by more than

5 grams.

If the balancer fails any of the above tests, it should be checked by the

manufacturer for defects. Balancer calibration should be checked at least

every two weeks or whenever the balance readings are questionable.

16.3.4 On-vehicle balancing

If checking and/or correcting these components off the vehicle are not pos-

sible or do not correct the vibration, it may be necessary to balance the

tyre/wheel assemblies while they are mounted on the vehicle using an on-

vehicle, high-speed balancer (Fig. 16.19). This will balance the hubs, rotors

and wheel simultaneously. Also it can compensate for any amount of resid-

ual run-out encountered as a result of mounting the tyre/wheel assembly

on the vehicle, as opposed to the balance that was achieved on the off-

vehicle balancer.

Follow the on-vehicle balancer manufacturer’s operator’s manual for

speciﬁ c instructions while keeping the following tips in mind:

• Do not remove the off-vehicle balance weights. The purpose of on-

vehicle balance is to ‘ﬁ ne tune’ the assembly balance already achieved,

not to start all over again.

• Leave all wheel trim installed whenever possible. Some wire wheel

covers have been known to induce static imbalance. If you suspect wheel

trim to be causing the vibration, it can be eliminated by road testing the

vehicle with the wheel trim removed. Remember the process of elimina-

tion: it works.

16.19 Balancing on-vehicle wheel by means of on-vehicle balancer.

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