Why Does the Car Body Shake at High Speeds?

[McSebastian]

There are several reasons why the car body may shake during high-speed driving: 1. Uneven brake disc surface with excessive radial runout. During braking, the contact between the brake pads and the brake disc varies, leading to inconsistent braking force and causing the car body to shake. 2. Significant deviation in wheel alignment data, especially incorrect front wheel alignment angles or excessive toe-in. This makes the vehicle harder to control during acceleration, with generally minor shaking but an uncomfortable driving experience. 3. Improper tire pressure—either too high or too low. Over-inflated tires cause more pronounced shaking at higher speeds, while under-inflated tires lead to a floating sensation and veering. 4. Abnormal tire wear due to misaligned wheels or deformed rims, resulting in uneven tire surface wear and causing body shaking during driving. 5. Deformed rims, which cause the tires mounted on them to also deform, leading to an uneven surface and imbalanced wheel dynamics. 6. Failed shock absorbers, which transmit road impacts directly to the car body without damping, causing overall body shaking. 7. Issues with tire dynamic balance. 8. Half-shaft resonance, usually caused by a bent half-shaft (in front-wheel-drive cars) or drive shaft (in rear-wheel-drive cars), disrupting the dynamic balance and creating resonance at certain speeds. 9. After torque converter lock-up, the engine output and transmission input become rigidly connected. If not released promptly during braking, the transmission can drag the engine, causing shaking. 10. Ignition and fuel supply faults, such as insufficient ignition energy, misfiring, or inadequate fuel pump supply under high-speed, high-load conditions, leading to sudden engine power loss. 11. For fuel efficiency, vehicle designs may shift gears early at high speeds, engaging higher gears at low engine RPMs. This can cause slight shaking due to insufficient power, which resolves once the RPM range is passed, with no impact on driving performance and improved fuel economy.