What is an Alignment?
While it is often referred to a simple "alignment" or "car alignment," an alignment is actually complex suspension angles that are measured and a variety of suspension components that are adjusted. This makes a car alignment an important suspension-tuning tool that greatly influences the operation of the vehicle's tires.
Out-of-alignment conditions occur when the suspension and steering systems are not operating at their desired angles. Out-of-alignment conditions are most often caused by spring sag or suspension wear (ball joints, bushings, etc.) on an older vehicle. They can also be the result of an impact with a pothole or curb, or a change in vehicle ride height (lowered or raised) on any vehicle regardless of age.
Incorrect car alignment settings will usually result in more rapid tire wear. Therefore, car alignment should be checked whenever new tires or suspension components are installed, and any time unusual tire wear patterns appear. Car alignment should also be checked after the vehicle has encountered a major road hazard or curb.
During a front-end car alignment, only the front axle's angles are measured and adjusted. Front-end car alignments are fine for some vehicles featuring a solid rear axle, but confirming that the front tires are positioned directly in front of the rear tires is also important.
Solid rear axle vehicles require a thrust angle car alignment that allows the technician to confirm that all four wheels are "square" with each other. Thrust angle car alignments also identify vehicles that would "dog track" going down the road with the rear end offset from the front. If the thrust angle isn't zero on many solid rear axle vehicles, a trip to a frame straightening shop is required to return the rear axle to its original location.
Thrust Angle Alignment
On all vehicles with four-wheel independent suspensions or front-wheel drive vehicles with adjustable rear suspensions, the appropriate alignment is a four-wheel car alignment. This procedure "squares" the vehicle like a thrust angle alignment, and also includes measuring and adjusting the rear axle angles as well as the front.
Not all vehicles are easily adjustable or fully adjustable. Some vehicles require aftermarket kits to allow sufficient adjustment to compensate for accident damage or the change in car alignment due to the installation of lowering springs.
When aligning a vehicle, it's appropriate for the vehicle to be carrying its "typical" load. This is important for drivers who continuously carry loads in their vehicles, such as sales representatives with samples or literature in the trunk. Additionally, when a vehicle is used for autocross or track events, some racers will sit in their car, or have the car alignment shop "ballast" their vehicle to include the influence of the driver's weight on the suspension angles.
The vehicle manufacturers' car alignment specifications usually identify a "preferred" angle for camber, caster, and toe (with preferred thrust angle always being zero). The manufacturers also provide the acceptable "minimum" and "maximum" angles for each specification. The minimum and maximum camber and caster specifications typically result in a range that remains within plus or minus 1-degree of the preferred angle.
If for whatever reason your vehicle can't reach within the acceptable range, replacing bent parts or an aftermarket car alignment kit will be required. Fortunately, there is a kit for almost every popular vehicle due to the needs of body and frame shops doing crash repairs and driving enthusiasts tuning the suspensions on their cars.
An accurate wheel alignment is critical to balance the tread wear and performance a vehicle's tires deliver. Regular wheel alignments will usually save you as much in tire wear as they cost, and should be considered routine, preventative maintenance. Since there are "acceptable" ranges provided in the manufacturer's recommendations, the technician should be encouraged to align the vehicle with the preferred settings and not just within the range.
If you are a reserved driver, aligning your vehicle to the vehicle manufacturer's preferred settings is appropriate.
Many of today's car alignment machines are equipped with printouts that compare the "before" and "after" alignment angles with the manufacturers' specifications. Requesting a post-alignment printout can help you confirm the thoroughness of the car alignment technician and preserve a record of your vehicle's intended settings in the case of an encounter with a suspension damaging road hazard.