Caution: Refer to Work Stall Test Caution in the Preface section.
Wheel imbalance causes most highway speed vibration problems. A vibration can remain after dynamic balancing if any of the following conditions are present:
| • | A tire is out of round (2) |
| • | A rim is out of round (4) |
| • | A tire stiffness variation exists (3) |
Measuring tire and wheel free runout will uncover only part of the problem. All 3 causes, known as loaded radial runout (1), must be checked using the method of substituting a known good tire and wheel assembly on the problem vehicle.
Low-speed vibrations, which occur below 64 km/h (40 mph), are usually caused by runout. High-speed vibrations, which occur above 64 km/h (40 mph), can be caused by either imbalance or runout.
There are 2 ways to correct properly balanced tires which still vibrate. One method uses an automatic machine which loads the tire and buffs small amounts of rubber from high spots on the outer 2 tread rows. Correction by this method is usually permanent and, if it is done properly, does not significantly affect the appearance or the tread life of the tire. Tire truing with a bladetype machine is not recommended because it substantially reduces the tread life and often does not correct the problem permanently.
Another method is to dismount the tire and rotate it 180 degrees on the rim. Do this only on the tire and wheel assemblies which are known to be causing a vibration because this method is just as likely to cause good assemblies to vibrate.
