As a result of advancements in automotive technology, today’s tire and wheel/rim fitments require special attention. By design, radial tire construction and low aspect ratios contribute to a vehicle’s ride and handling quality. Proper tire mounting, balancing and installation are critical to attaining a smooth vehicle ride. Vehicle vibration and a suspected problem tire may actually be due to an improperly balanced tire and wheel assembly or related to the mechanical condition of the vehicle. BALANCING 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 new, high performance or luxury vehicles may be more sensitive to imbalance problems, but no driver is happy with an annoying vibration. An out-of-balance tire and wheel assembly:
• Degrades ride quality and driver comfort.
• Shortens the life of tires, bearings, shock absorber, and other suspension components. Vibration is the most noticeable effect of imbalance.
• It is dependent on vehicle speed and may be felt in the steering wheel, seats or floor board.
• It often first becomes apparent between 40 and 45 mph and changes in magnitude with greater speeds. Because of this, Yokohama customers with ride complaints, especially those with original equipment tires, should be serviced according to Rubber Manufacturers Association (RMA) guidelines and this Yokohama bulletin. RMA publications can be obtained directly by calling (202)682-4800, or accessing their website-www.rma.org/. Ask for “Care & Service of Automobile and Light Truck Tires” publication. To properly diagnose vibration complaints, it is important to first understand the types and causes of imbalance. TYPES OF IMBALANCE See Figure 1 On Page 3 Static Imbalance: Vertical movement resulting from heavy or light spots in a tire. Can be corrected using either a static “bubble” balancer or dynamic “spin” balancer. Dynamic Imbalance: Lateral movement (wobble or shimmy) resulting from unequal weight on both sides of the tire and wheel/rim assembly’s circumferential centerline. Can only be corrected using a dynamic “spin” balancer. Run Out Imbalance: Excessive radial and/or lateral movement resulting from tire or wheel/rim non-uniformity, improper bead seating, or improper match mounting of the tire and wheel/rim assembly. This can be corrected by measuring the amount of tire and wheel/rim assembly run out (lateral and radial) with a gauge, and replacing the component having excessive run out. Vehicle Imbalance: Vibration due to faulty vehicle components other than the tire or wheel/rim assembly; such as hubs, brake rotors and drums, and drive lines. Correction requires checking for any irregularities, and replacement as required. 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.

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