Road or wind conditions are bad.

Test the vehicle. Drive the vehicle in both directions on a flat road.

The front wheels are misaligned.

Adjust the wheels to specifications.

Refer to Wheel Alignment Measurement in Wheel Alignment.

The steering gear valve is unbalanced.

If the steering gear valve is unbalanced, steering effort will be light in the direction of the lead and heavy in the opposite direction of the lead.

Replace the gear valve.

The steering shaft is rubbing the ID of the shaft tube.

Align the column.

The tires are worn or bad.

Replace the tires.

Refer to Tire Mounting and Dismounting in Wheels and Tires.

There is low pressure in the tires.

Adjust the tire pressure.

Refer to Tire Inflation Pressure Specifications in Maintenance and Lubrication.