When I m driving slowly, like 30km/h, my car shakes, its not the string ok, but when I drive like 40km/hr it will be ok and when I got at the speed of 100km/hr the string shakes a bit, but my tire is new, with 195/50 r 15, I checked it three mechanics but they said the tire is bad but which is not, I already checked and put balance on each wheel, what shall I do about it, thank you so much !
Defective new tires is not unheard of but not as common as in the past. Balance is not the issue. Have them balanced on a "road-force" balancer. That will show up variations in how the sidewalls flex in different areas, and it will show up a bent wheel. If they all pass, have the wheels measured for "lateral runout" on the car. If a wheel is found to be wobbling sideways as it rotates, look for debris sticking between the brake rotor and wheel or that fell between the brake rotor and hub.