The technical definition of balance is the uniform distribution
of mass about an axis of rotation, where the center of gravity
is in the same location as the center of rotation. A balanced
tire is one where mass of the tire-when mounted on its wheel and
the car's axle-is uniformly distributed around the axle (its center
of rotation). Balanced tires can spell the difference between
a positive and negative driving experience. Drivers of high performance
vehicles will be more sensitive to imbalance problems, but no
driver is happy with an annoying vibration.
An out-of-balance tire and
Degrades ride quality and driver
Shortens the life of tires, bearings,
shock absorbers, and other suspension components. Vibration
is the most noticeable effect of imbalance.
It is dependent on vehicle speed.
It often first becomes apparent between
40 and 45 mph and increases in magnitude with greater speeds.
Sources of Imbalance
Two sources of imbalance occur in tires:
heavy or light spots in the tire and radial or lateral run-out.
Imbalance also can be caused by:
Variations within the wheel, such
as thickness and welds.
Rotor and axle imbalances.
Heavy or Light Spot Imbalance
There are two types of imbalance caused
by heavy or light spots: static and dynamic.
imbalance: Occurs when
there is a heavy or light spot in the tire so that the tire
won't roll evenly and the tire/wheel assembly undergoes an up-and-down
imbalance: Occurs when
there is unequal weight on both sides of the tire/wheel assembly's
circumferential centerline. The tire/wheel assembly has a side-to-side
Heavy or Light Spot Balancing
Achieved either statically or dynamically,
depending on the type of imbalance that has occurred.
balance: Achieved with a bubble balancer but does not
correct for dynamic imbalance.
balance: Achieved with a spin balancer where the tire/wheel
assembly is balanced both statically and dynamically.
Radial or Lateral Run-out
This results from poor bead seating
on the rim or the placement of components. Poor bead seating is
usually the result of improper mounting or the use of improperly
made wheels. A small degree of this imbalance is acceptable, but
too great a run-out causes vibration and excessive tire wear.
Run-out: An "out-of-round" situation where vibrations
are produced as the wheel spindle moves up and down.
Run-out: A side-to-side or wobbling movement of the tire
and wheel. It is less common than radial run-out. Sensitivity
of a vehicle to vibration from radial run-out is four to eight
times that of wobble from lateral run-out.
Depends on whether it is radial or
Radial run-out balancing:
Achieved by rotating the wheel and tire assembly two stud positions
on the hub, or by rotating the tire 180° on the wheel. If run-out
is still over specification, check wheel run-out and mark the
low point. Rotate to match the high point of the assembly run-out
with the wheel low point. If the assembly run-out is still too
high and the wheel is within specification, replace the tire.
Lateral run-out: Achieved
by using a run-out gauge to check both the tire and wheel. Chalk-mark
the highest point of run-out on both the wheel and tire. Replace
whichever (wheel, tire, or both) is out of specification.
Wheel is securely seated on the
All lugs have proper torque.
There is no buildup of dirt between
the hub and wheel.
The wheel is not bent.
Both tire beads are securely seated
on the rim.
Custom or Alloy Wheels
Custom or alloy wheels require
an increased level of care over steel wheels. There
are several key points to note when mounting tires.
Avoid scratching or bending
alloy wheels during installation.
These wheels are manufactured with
extremely soft metals with a greater sensitivity to scratching
and distortion under pressure. Modern tire machines apply equal
pressure to both top and bottom beads with no pressure on the
wheel itself. A pad on the base of the mounting machine protects
chrome-plated, painted or machined wheels from scratches and damage.
During the mounting process,
is a must.
Both top and bottom beads must be lubricated
with an approved tire lubricant. If the beads do not seat at 40
psi, the installer must break the entire assembly down and re-lubricate the bead
Proper tire and wheel assembly balancing
is important from a vehicle safety standpoint. In high-speed driving,
improperly balanced tire/wheel assemblies will cause a vehicle
to lose stability and not operate in a safe and comfortable manner.
Improperly balanced tire/wheel assemblies also cause abnormal
To facilitate proper balancing,
Most tire manufacturers place red and yellow marks on the sidewalls of its tires
to enable the best possible match-mounting of the tire/wheel assembly.
There are two methods of match-mounting tires to wheel
assemblies using these red or yellow marks:
Uniformity (red mark)
Weight (yellow mark)
underinflation, overloading or tire damage may result in tire
failure, which may lead to serious injury. Tire and rim sizes
must correspond for proper fit and application. Never exceed 40
psi to seat beads.
Tire changing can be dangerous, and should be done only by trained
persons using proper tools and procedures established by the Rubber
Manufacturers Association. Failure to comply with proper procedures
may result in incorrect positioning of the tire, tube, or wheel
assembly, causing the assembly to burst with explosive force sufficient
to cause serious physical injury or death. Never mount or use
damaged tires, tubes, or wheel assemblies.
When performing uniformity match-mounting,
the red mark on the tire, indicating the point of maximum radial
force variation, should be aligned with the wheel assembly's point
of minimum radial run-out, which is generally indicated by a colored
dot or a notch somewhere on the wheel assembly (consult manufacturer
for details). Radial force variation is the fluctuation in the
force that appears in the rotating axis of a tire when a specific
load is applied and the tire rotated at a specific speed. It is
necessary to minimize radial force variation to ensure trouble-free
installation and operation. Not all wheel assemblies indicate
the point of minimum radial run-out, rendering uniformity match-mounting
sometimes impossible. If the point of minimum radial run-out is
not indicated on a wheel assembly, the weight method of match-mounting
should be used instead.
When performing weight match-mounting,
the yellow mark on the tire, indicating the point of lightest
weight, should be aligned with the valve stem on the wheel assembly,
which represents the heaviest weight point of the wheel assembly.
After match-mounting by either of the above methods, the tire/wheel
assembly can be balanced.