Seat Vibration 2002 Buick Lasaber

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Tom, my dad sold tires for several decades; I sold cars for 30+ years; we were both highly sensitive to non-smooth riding tires. The number 1 cause of vibration such as you describe, AFTER spin-balancing tires, was tires being out-of-round. Just because you tried 2 different tire sets doesn't eliminate this possibility. And it is easy to verify yourself. Your description indicates a rear vs. front end problem. Assuming so, check the rear tires for *out of round* ; remember, a box can be installed onto an axle, spin-balanced, and rotate smoothly--and yet it definitely won't ride smooth! Check them by raising them just an inch or so above ground. Lay an oil bottle (or 10-inch block of 2X4) squarely on its side and up close to a tire. Carefully spin the tire, by hand, and watch how close the tire's circumference approaches the stationary *reference object* as it rotates. High spots will narrow the gap, and low spots will widen the space(DUH!). If found out of round, have them trued and then balanced, and enjoy the quiet, smooth ride Lesabres are capable of. If all tires were so checked, my bet is a surprisingly high % of them would show excessive out-of-round. Such tires will often ride smoothly at all but certain speed-ranges. Only those w/o excessive runout will ride smoothly at all speed ranges. HTH, s

Tires and rims were used from another car that I drove and did not experience the vibration. Put them on my car and the vibration is still there.