Sen. John Kerry chats with a student working on an automobile wheel alignment during Kerry’s 2004 bid for the U.S. presidency.

AP Photo/Elise Amendola

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How do I know when my car needs to be realigned?

If you're wondering whether your car needs an alignment, first look at your tires. Uneven tire wear -- often, more wear on the outside of some tires -- is a prime indicator that your car is likely out of alignment. Here are a few more indicators:

  • your car seems to be drifting to one side, even when you think you're driving straight
  • your steering wheel vibrates
  • you are driving straight, but your steering wheel isn't centered

If none of these indicators occurs but it's been a while since your last alignment, check your owner's manual to see how often the manufacturer recommends having this service.

An out-of-alignment car is a common result of everyday driving. But the term alignment doesn't really refer to your car's wheels but rather to the suspension. As part of normal driving, parts of your car's suspension may become worn, and springs can be stretched out. Even a small accident or bumping a curb can disrupt your suspension, knocking some of the highly calibrated components off-kilter, making your wheels sit at improper angles. An alignment restores these angles to their correct measurements, making sure that your wheels sit straight.

The most visible benefit of an alignment is less tire wear. And when tires do wear down, they'll do so evenly on a properly aligned suspension. Tires can be quite expensive -- easily $100 or more per tire -- whereas an alignment often costs $50 to $100, making it a cost-effective procedure that should be part of regular car maintenance [source: Consumer Reports].

An alignment will ensure that your car drives straight and handles properly, making your ride safer. You'll also get better gas mileage because your tires will be properly aligned with the road, decreasing resistance.

On the next page, we'll look at what happens during an alignment.

A wheel alignment machine like this one is a key tool in restoring a suspension to its proper alignment.

© iStockphoto.com/sumbul

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What happens during an alignment?

A car alignment is actually an elaborate process that brings the car's suspension into its proper configuration, positioning and adjusting components so that wheels are aligned with one another and the road surface. The alignment should be performed by an experienced mechanic, who uses an alignment machine.

Newer alignment machines feature clamplike devices that are attached to the wheels of the car (which is raised up in the air) and that link to a computer that helps make precise measurements. The mechanic will also take this opportunity to make sure that no suspension components are excessively worn or broken.

An alignment essentially requires squaring a car's wheels and axles with each other so that they're moving in the same direction. The mechanic adjusts the various suspension angles -- known as toe, thrust, camber and caster -- that influence tire movement and position. The technician will also ensure that the steering wheel is centered.

Each car's manufacturer designates standard angles for the alignment, specified in degrees. If you're a driver of a high-performance car or sports car, your mechanic may be able to align your suspension to improve handling and tire performance, but such an alignment still may lead to uneven tire wear.

The type of alignment you receive will depend on your car's suspension. A four-wheel alignment is reserved for all-wheel drive vehicles or front-wheel drive vehicles with independent or adjustable rear suspensions. In this case, both axles have to be properly aligned so that all four wheels align in a rectangle, parallel to one another and perpendicular to the ground.

If you don't have a four-wheel or all-wheel drive vehicle, your car will likely only require a front-end alignment, in which only the front-axle components are adjusted, or a thrust-angle alignment. Thrust angle refers to the angle that a car's rear wheels point relative to the car's center. In such an alignment, the rear wheels and axle are realigned so as to be parallel with the front axle and perpendicular to the center line of the car.

After the alignment is complete, it's appropriate to ask for a printout -- which many mechanics now provide -- that shows before and after images of the suspension alignment.

For more information about car maintenance and related topics, please look over the links on the next page.

Lots More Information

Related HowStuffWorks ArticlesSources
  • Consumer Reports. "Tales of repair woes." September 2009.http://www.consumerreports.org/cro/magazine-archive/september-2009/cars/car-problems/tales-of-repair-woe/car-problems-tales-of-repair-woe.htm
  • Hunter Engineering Company. "What Everyone Should Know About Wheel Alignment." 2009.http://www.hunter.com/pub/undercar/2470T/index.htm
  • Ofria, Charles. "A Short Course on Wheel Alignment." Family Car. 2007.http://www.familycar.com/alignment.htm
  • Petersen, Gene. "Tires Q&A: Problem solving irregular wear." Consumer Reports. September 2009.http://blogs.consumerreports.org/cars/2009/09/tires-qa-problem-solving-irregular-wear.html
  • Tire Rack. "Tire Tech Information - Alignment."http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4