It is not normal, the right and left wheel don't align properly and it could be the tyres. Over the miles, turning left and right, hitting bumps and holes you could not see or avoid, and driving down uneven road surfaces have led to uneven treadwear on your tyres. Perhaps a pothole has knocked-out your vehicle's alignment (this creates uneven tyre wear).
Very often the wheel/tyre assemblies on a vehicle may be in balance but you still feel a vibration. Here are some of the other causes of vibration:
• Bent wheel
• Tyre out of round (radial or lateral runout)
• Wheel to axle mounting error
• Inconsistent tyre sidewall stiffness (force variation)
• Brake component wear or failure
• Drive train or engine component wear or failure
• Suspension wear or failure
• Wheel bearing wear of failure
• Wheel alignment is out
