February 22, 2013

Car Talk

High tire pressure can cause bounce

Syndicated columnists

Dear Tom and Ray:
I took my 2002 Infiniti I35 to a shop to have the rotors and brake pads replaced on the front. While in the shop, the mechanic told me that I would need new struts in the future. When I left the shop, my car was bouncing all over the place. I was driving on a paved road, and I was actually bouncing off the seat. When I took it back to the shop, I was told that when they had put the car on the lift, air got into the struts because there were tiny holes in them. The mechanic told me it would go back to normal in a few weeks ... as soon as all the excess air leaked out of the struts. Is his explanation plausible? Patricia

Ray: No. He made that up, Patricia.

Tom: Changing the rotors and pads shouldn't have had any effect on the ride, so I don't know what they did to your car to make it ride so roughly — but I have a couple of suspicions.

Ray: The most likely cause, in our experience, is that they inflated your tires, or overinflated them.

Tom: If, before the repair, you had been driving around with tires that were low on air, that could have covered up the poor ride you'd get from bad shocks.

Ray: And then, once they properly inflated your tires, you felt the full effect of your worn-out shocks — in which the springs are undamped and the car kind of rides like a basketball down the road.

Tom: Of course, it's not safe to drive with underinflated tires (or worn-out shocks), so you can't just let some air out of the tires and keep driving.

Ray: But they also could have grossly overinflated your tires. If they weren't paying attention, or had a tire gauge that was faulty, they could have put 60 or 80 pounds of air in your tires. And that certainly would cause you to bounce off the seat.

Tom: Have someone check the pressure for you, and if the pressure is correct, then go somewhere else for a second opinion about the shocks.

(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)

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