All Lined Up
Wouldn't it be great if you could improve the steering response, cornering ability, and gas mileage of your vehicle in less than an hour and for less than $50? It may sound like something you'd hear on a late-night infomercial being plugged by a has-been celebrity, but if you haven't had your vehicle aligned in the last year, it's also a real possibility.
Front-end alignments, like wheel balancing, radiator flushes and brake jobs, are neglected services. Almost everyone who owns a car or truck knows that these jobs have to be performed from time to time, yet rarely does anyone worry about them until a drastic problem occurs (like a strong vibration during highway travel or a steaming radiator on hot days). Alignment problems can be particularly difficult to detect because they usually happen over a long period of time, with only minor changes in how a vehicle drives. There are often no visible or audible cues to alert owners of a problem, leaving only a subtle "feel" that suggests something is amiss.
A total of six measurements play a role in vehicle alignment. Three of these (caster, camber and toe) are commonly adjusted during a front-end alignment procedure. The other three (wheelbase, track and ride height) are intrinsic to vehicle design and are not meant to be regularly altered.
This is a crucial measurement for handling purposes. It refers to the difference between the front tires' vertical centerline and the centerline of the steering axis through the upper and lower ball joints. Think of all those globes you saw while growing up. Remember how the Earth was tilted slightly with the line between the South and North Poles at an angle? This is akin to the steering angle on your front tires. If you were to tilt the Earth even more, thus making its axis less vertical and more horizontal, you would be increasing, or making more positive, the caster measurement (for the purposes of our analogy). More positive caster provides improved stability and self-centering in a vehicle's steering, but it also makes the steering heavy, especially at low speeds. Manufacturers usually set this between +2 and +6 degrees for the best all-around driving traits.
If you were to stand directly behind or in front of one of your tires to view its vertical angle, you would be looking at its camber. Actually, camber is most often set between 0 and -2 degrees, so you'd be hard pressed to see any lean at all. Negative camber refers to a wheel that is leaning inward with its top closer to the vehicle than its bottom. Positive camber, surprise-surprise, is the opposite, and means that a wheel leans out with its top further from the vehicle than its bottom. Many of the original Volkswagen Beetles had noticeable negative camber in the rear tires which made them look like they were squatting all of the time. A slight amount of negative camber setting is desirable because as a vehicle turns the outside wheels get pushed into a more positive camber state. This results in a camber of zero, or a straight up-and-down wheel, while cornering, which provides the largest contact patch and the greatest traction for handling.
Picture yourself hanging from an engine hoist directly over the front axle of your vehicle. Now imagine you've got X-ray vision and, for now at least, you're going to look through your car's hood and fenders to see the front wheels (there will be time to look through people's clothes later). At this point, you would be seeing the measurement of toe in your front-end. Toe is the angle of two wheels on the same axle, in relation to each other. For instance, if your front tires both pointed directly straight ahead and were parallel to each other, you would have zero toe. If the front of the tires were closer together than the rear, this would be toe-in, and if the rear were closer than the front, toe-out. Toe plays a major role in how a car feels going through a corner with toe-in creating more understeer and toe-out increasing oversteer. This is also where gas mileage can be improved since a vehicle with too much toe will be creating excessive friction and using up fuel (and tires) faster than it should. Toe settings vary from car to car and are determined by many factors including drivetrain layout and vehicle design.
This is the measurement between the center of the front wheels and the center of the rear wheels, and it should be the same on both sides of a vehicle. Unless some form of serious custom work is being done, a vehicle's wheelbase should never be altered. If it is unequal between the two sides, something is probably bent or broken.
The distance between the frame and the ground is a vehicle's ride height. This can be altered with aftermarket springs (or by cutting the original springs) but it is not recommended since the entire suspension design of a vehicle is based largely on its original ride height. Also, if ride height varies more than a quarter-inch between sides, handling will be compromised and an inspection of the various components should be performed. Sagging springs or a blown-out shock are likely to be the cause.
Track is the distance between the center of the tires on the same axle. It is basically how wide of a footprint the vehicle has. Using offset wheels, or wheels with a different centerline in relationship to the axle hub, can alter it. A negative offset will increase a vehicle's track while a positive offset will bring the tires closer together. Of course, if you believe the Pontiac ads, "Wider is better," you'd want more negative offset for increased stability. But, like all modifications, this can be detrimental if taken too far.
The preceding six terms are thrown about with reckless abandon when you go for an alignment, but few shops actually explain what they mean. Now, you have a basic understanding of what these measurements are and how they affect handling. If you suspect that one or more of these setting is off on your car and you haven't received an alignment in the last 12 months, schedule a visit to your local service center, and get things back in line.