“Shake” is defined as vertical or lateral vibration of the vehicle body and steering wheel, along with vibration of the seats. Shake usually cannot be felt below a speed of about 80 km/h (50 mph). Above this speed, shake increases markedly but then peaks at a certain speed.
The frequency of the vibration called “shake” is similar to the frequency of the vibrations made by an impact wrench when it is being used to tighten nuts, etc.
Excessive tire run-out, imbalance or unevenness
Resonances among engine, springs, steering wheel, seats, and body
1.Runout and imbalance of a tire will cause the tire to generate a vibrating force during vehicle operation.
2.This vibration is amplified and in turn causes the axles to vibrate.
3.And the vibration of the axles is transmitted to the vehicle body and the engine through the suspension.
4.When the transmitted vibrations resonate with the vehicle body, the body vibrates strongly. In addition, when the vibrations of the axles resonate with those of the engine, the engine vibrates vigorously, which in turn, causes the body to vibrate even more.
5.These body vibrations are transmitted to the steering wheel and seats, causing the body, seats, and steering wheel to vibrate.
Sometimes the body may shake alternately in the vertical and lateral directions at approximately 10-second intervals. This is due to slight differences in the turning radii of the tires, which create differences in relative runout points between the right and left tires, or between the front and rear tires. For this reason, while test driving for body shake, it is important to maintain the same speed for at least 10 seconds at a time, before going on to another speed.
Body shake usually occurs due to unbalanced or unevenly worn tires; for this reason, most body shake can be eliminated by correcting tire balance or reducing runout.