While driving at a certain speed, the steering wheel chatters towards the direction of rotation of the steering wheel. When a car steering wheel vibrates and the vibration is towards the direction of rotation of the steering wheel, this steering problem is called shimmy. Steering shimmy is defined as the vibration in the rotational direction of the steering wheel when the vehicle is running at a certain speed.
You can check if your car is suffering from steering wheel shimmy by accelerating your car slowly to 100 km/h and maintaining that speed for a short period of time and feeling the steering vibration by softly touching the steering wheel with your fingers. Be sure not to make a sudden acceleration or full braking for safety reasons.
During vehicle operation, the tire rotates. As the tire rotates, there is constant tire flexing and deflection in response to vehicle speed and load. Uneven tread rubber thickness and/or poor carcass and cord connection will produce irregular tire deflection resulting in shimmy, shaking, abnormal noise, and other vibrations. This will occur even if the vehicle load and speed are constant. Irregular tire deflection (hardness and rigidity changes) is called force variation. Force variation affects the upper and lower tire areas, the tire sides, and the leading and trailing edges of the tire/road surface contact area.
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Several reasons cause steering wheel shimmy such as unbalanced front tire and road wheel, vibration from the irregular road surface, and unbalanced objects rotating with the front tire and road wheel to name a few. When the vibration occurs on the latter causes of problems it will transmit to the steering linkage into the steering wheel, thus resulting in car steering problems such as steering wheel shimmy.
The following items are typical causes of steering shimmy
1. Tire malfunction (radial runout, unbalance)
2. Condition of road surface
3. Brake system malfunction
4. Steering system malfunction
5. Suspension system malfunction
6. Wheel alignment malfunction
What to do?
A tire malfunction is the most likely cause of steering shimmy among the causes listed above. Why does the steering shimmy occur with an unbalanced tire? Vibration caused by an unbalanced tire is transmitted to the steering wheel via the steering system, which results in a steering shimmy.
Since the usual cause of shimmy can be pointed out to be an imbalance tire and road wheel, the solution is to bring the car to a reputable auto repair shop and ask the mechanic to perform tire balancing on the car. This should fix the steering wheel shimmy. But before bringing the car to a car shop check first the tire pressure, sometimes it's just a simple adjustment of tire pressure into the manufacturer specified tire pressure value that can correct steering wheel shimmy.
Tire and wheel unbalance are felt most acutely at high vehicle speeds. It results in vibration and abnormal noise. Vehicle stability and operating safety are adversely affected. Tire wear is accelerated. Differences in vehicle tire weight lead to loss of driving stability and abnormal vibration. Weight unbalance may be either static (single plane) or dynamic (two planes due to tire width). The wheel consists of the tire and the road wheel. Wheel balance improves vehicle operating stability. Unbalanced wheels cause excessive vehicle vibration and instability.
Wheel balancers are used to adjust the balance of individual wheels. There are two types of wheel balancers. The off-car wheel balancer requires the removal of the wheel from the vehicle. The on-car wheel balancer does not. The on-car balancer supports the vehicle axle or hub during the balancing procedure, and can only balance the tire statically. It is, therefore, recommended for diagnoses of driveline vibration problems only.
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