Here's why:
* Tire Balance: An imbalance in a tire (or tires) will cause a vibration that's felt most strongly at a specific speed. The heavier side of the unbalanced tire will be flung outwards with greater force at higher speeds, increasing the vibration. However, at very high speeds, the forces may somehow balance themselves out (or be less noticeable among other road forces), leading to a reduction in shaking. 40 mph is a common speed range for this type of imbalance to be most noticeable.
* Wheel Balance: Similar to tire balance, an unbalanced wheel (even if the tires are balanced) can cause this issue. Weight imbalances in the wheel itself can create vibrations that are speed-dependent.
* Tire Wear: Uneven tire wear (cupping, feathering) can also cause vibrations that are more pronounced at certain speeds. Again, the vibration's amplitude may change as speed increases.
* Less Likely, But Possible: While less likely given the speed range, warped rotors or a slightly bent wheel could also contribute, but these usually cause a vibration that's more constant across speed ranges, rather than disappearing at 60 mph.
To diagnose the problem:
1. Visual Inspection: Carefully inspect your tires and wheels for any obvious damage, uneven wear, or anything out of the ordinary.
2. Tire Rotation: Rotate your tires (if you haven't recently) to see if the shake changes or moves to a different wheel. This helps isolate if it's a tire or wheel issue.
3. Wheel Balancing: Take your vehicle to a tire shop and have them balance all four wheels. This is the most likely solution.
4. Tire Condition: Have a tire professional assess the condition of your tires for uneven wear. If necessary, replacement might be needed.
It's crucial to address this issue promptly. Ignoring a steering wheel shake can lead to further damage to your vehicle's suspension and steering components.
