Yokohama EN

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 tyre is one where mass of the tyre - when mounted on its wheel and the car's axle - is uniformly distributed around the axle (its center of rotation). Balanced tyres 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 tyre and wheel assembly:

• Degrades ride quality and driver comfort.
• Shortens the life of tyres, 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 50 and 60 km/h and increases in magnitude with greater speeds.

Sources of Imbalance

Two sources of imbalance occur in tyres: heavy or light spots in the tyre 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.

• Static imbalance: Occurs when there is a heavy or light spot in the tyre so that the tyre won't roll evenly and the tyre/wheel assembly undergoes an up-and-down movement.
• Dynamic imbalance: Occurs when there is unequal weight on both sides of the tyre/wheel assembly's circumferential centerline. The tyre/wheel assembly has a side-to-side movement.

Heavy or Light Spot Balancing

Achieved either statically or dynamically, depending on the type of imbalance that has occurred.

• Static balance: Achieved with a bubble balancer but does not correct for dynamic imbalance.
• Dynamic balance: Achieved with a spin balancer where the tyre/wheel assembly is balanced both statically and dynamically.

Radial or Lateral Run-out Imbalance

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 tyre wear.

• Radial Run-out: An "out-of-round" situation where vibrations are produced as the wheel spindle moves up and down.
• Lateral Run-out: A side-to-side or wobbling movement of the tyre 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.

Run-out Balancing

Depends on whether it is radial or lateral run-out.

• Radial run-out balancing: Achieved by rotating the wheel and tyre 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 tyre.
• Lateral run-out: Achieved by using a run-out gauge to check both the tyre and wheel. Chalk-mark the highest point of run-out on both the wheel and tyre. Replace whichever (wheel, tyre, or both) is out of specification.