U-bolts are used to hold springs to the front and rear axles of your car. They are also used to attach the body of a truck to its frame. Over time, U-bolts can become loose or worn and should periodically be tightened.
Shaped like a “U” and aptly named, the U-joint connects the two shafts of the driveshaft. Over time, lubrication inside the U-joint will wear out causing the gears to rub against one another and damage the mechanism.
Underinflation of a tire affects driving performance, wears the tire out more quickly and reduces fuel efficiency. An under inflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. Not only does this put you at risk of getting a flat tire, it significantly shortens the life of your tire. That’s why you should frequently check your tire pressure to make sure all four contain the prescribed air pressure (usually indicated on a sticker on the interior edge of the car door).
Underbody refers to the belly of your car, the underside that sits closest to the road. Everyday as you drive, rocks, road debris, and salt on snowy roads brushes up against the underbody of your car. When you bring your car in for service, it’s raised on a rack so that the mechanic can access certain components and inspect the underside of the car for damage or rust in order to prevent more serious conditions from developing.
Understeer is what happens when your car turns less than the amount you thought it would, causing you to veer off the road.