40-60 is a WIDE range for this effect. Like my car does it right at 60-65mph holding a steady speed. The tires arent exactly round on my car anymore. Any less than 40 and ur prob not going fast enough to cause the vibration. Is it 'vibrating' or actually 'wobbling'? I *think* theres a difference. If you guys check the steering stem torque like mentioned then the next thing i would do is remove the front wheel and take it down to a shop to have them put it on a balancer and spin it up.