- obvious signs of tire and wheel runout;
- obvious signs of drive shaft beating;
- the air pressure in the tires must be normal;
- violation of the normal height of the static position of the body;
- wheel rim deformations;
- deposits on tires and wheels,
- loose or missing balancing weights or mounting nuts;
- abnormal or severe wheel wear;
- correct fit of tires on wheel rims;
- tire defects such as delamination, bulging from impacts with road irregularities. Small dents on the sidewalls of the tire are not a defect and do not affect the performance properties of the tire or the smoothness of the car.
Wheel balancing is the simplest operation to eliminate chassis vibration at high speed, so it should be done first. It is necessary to dismantle the wheels and balance them dynamically on the stand. This allows you to eliminate all wheel balancing violations.
After the wheels have been mounted on the vehicle, final balancing can be performed. This operation allows you to eliminate the imbalance of the wheels together with the brake discs, drums and decorative caps.
If wheel balancing fails to eliminate vibration at high speed or vibration occurs at low speed, the possible cause is wheel runout. Wheel runout can be caused by tire runout, wheel rim runout, or improper tire/rim mounting. In this case, the following should be done:.
[Original version of the article on the website MitsubishiMan]
If there is any suspicion of runout, the runout value of the suspended wheel should be measured without dismantling it from the car. It is recommended to use a dial indicator with a feeler gauge for measuring. Axial runout should be measured along the sidewall of the tire as close to the shoulder as possible. Radial runout is measured along the central tread. In some cases (with a strongly dissected pattern of the central tread), it may be necessary to tightly wrap the tread with adhesive tape for better contact with the indicator feeler gauge.
When measuring axial or radial runout, do not take into account significant and short-term deviations of the indicator pointer, which are caused by local irregularities and the tread pattern. Record the resulting runout value and mark the position of the point on the tire with the maximum deviation. The runout value of the wheel installed on the car should not exceed 1.5 mm. If the runout is outside the permissible limit, perform the following operation.
If the measured axial or radial runout value on the vehicle exceeds 1.5 mm, remove the wheel, place it on the balancing stand and check the runout value again. Center the wheel on the stand using the central hole. Measure and record the wheel runout values following the recommendations in the previous paragraph and mark the position of the points with small deviations. Then measure the runout of the wheel rim. If the runout values obtained exceed the permissible limit, the wheel must be replaced. If the radial or axial runout of the wheel and tire assembly (measured by the tread) exceeds 1.27 mm, proceed to the next step.
If the radial or axial runout of the wheel exceeds 1.27 mm, the tire should be remounted on the wheel in such a position that the point of greatest radial deviation coincides with the point of least radial deviation of the wheel. Inflate the tire, mount the wheel on the balancing stand and re-measure the radial and axial runout. Note the position of the points with the greatest deviations. Such remounting of the tire often allows the runout to be reduced to a value not exceeding 1.27 mm.
If the runout of a wheel removed from a vehicle is normal, but runout measurements directly on the vehicle yield unacceptably high runout values, a possible cause is a violation of the wheel centering relative to the hub. Move the wheel in the circumferential direction by two hub studs, secure the wheel and re-measure the runout. Repeat a similar operation several times to find the best position for the wheel.
If the wheel runout cannot be reduced to an acceptable level, the wheel should be dismantled and the wheel hub runout measured. To do this, set the indicator to zero when touching the hub with a feeler gauge. Then carefully turn the hub. Measure and record the runout value. If the runout exceeds 0.76 mm, the hub must be replaced. After remounting the tire, which is associated with its replacement or change in circumferential position, it is necessary to balance the wheel assembly. In addition to wheel imbalance or runout, another cause of chassis vibration may be unequal radial rigidity of the tire in different sections (tire runout under load). However, the radial rigidity of the tire can only be checked on a special tire tester.
The tire tester is a support drum on which the car wheel rests. During the tire test, the drum rotates slowly. The vibration of the radial rigidity around the tire causes vertical movements of the wheel axis, which can be measured.
More advanced equipment allows not only to control the change in radial rigidity of a wheel removed from a vehicle, but also to partially correct the non-uniformity of a tire by removing a small layer of rubber from the tread in the most rigid sections of the tire. To control radial rigidity, as in the first case, the loaded wheel is rolled on a rotating drum. A tire tester and similar equipment provide the ability to simultaneously control the measurement of radial rigidity of tire and wheel runout. However, such stands are not always available, so the above-described method of monitoring the runout of a free wheel using an indicator is widely used in practice. Usually, the runout of a free wheel is associated with the location of the most rigid section of the tire.
An additional method can also be used to diagnose the causes of chassis vibration. The method involves completely replacing the car's wheels with known-good wheels and testing the car on the move. If the vibration has disappeared, gradually replace all the car's wheels one by one, returning the old ones to their place, and each time conducting road tests. This helps to identify a non-uniform wheel causing chassis vibration. The vibration of the radial rigidity of the tire depends on the direction of rotation of the wheel.