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Radial tire lead
"Lead" is the deviation of the vehicle from a straight path on a level rod even with no pressure on the steering
wheel.
Lead is usually caused by:
• Incorrect alignment.
• Uneven brake adjustment.
• Tire construction.
The way in which a tire is built can produce lead in a vehicle. An example of this is placement of the belt. Off
center belts on radial tires can cause the tire to develop a side force while rolling straight down the road. If one
side of the tire has a little larger diameter than the other, the tire will tend to roll to one side. This will develop a
side force which can produce vehicle lead.
The procedure in previous page should be used to make sure that front alignment is not mistaken for tire lead.
• Part of the lead diagnosis procedure is different from the proper tire rotation pattern currently in the owner
and service manuals. If a medium to high mileage tire is moved to the other side of the vehicle, be sure to
check that ride roughness has not developed
• Rear tires will not cause lead.
Vibration Diagnosis
Wheel unbalance causes most of the highway speed vibration problems. If a vibration remains after dynamic
balancing, its possible causes are as follows.
• Tire runout.
• Wheel runout.
• Tire stiffness variation.
Measuring tire and/or wheel free runout will uncover only part of the problem. All three causes, known as loaded
radial runout, must be checked by using a Tire Problem Detector (TPD). If TPD is not available, alternative
method of substituting known-good tire and wheel assemblies on the problem vehicle can be used, although it
takes a longer time.
[A] : Caused by tire out of round
[B] : Caused by tire stiffness variation
[C] : Caused by rim bent or out of round
1. Smooth road
2. Suspension movement (loaded runout)
STEERING, SUSPENSION, WHEELS AND TIRES 3-7
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