The wheel and tire out of balance

Refer to Front Wheel Shimmy in Suspension General Diagnosis.

A blister or bump on the tire

Replace the tire. Refer to Tire Mounting and Dismounting in Tires and Wheels.

Improper shock absorber action

Replace the shock absorber. Refer to Shock Absorber Replacement in Front Suspension.

Excessive wheel or tire runout

Refer to Front Wheel Shimmy in Suspension General Diagnosis.

Tire lead

Refer to Front Wheel Shimmy in Suspension General Diagnosis.