Auto Academy: Wheel Alignments
I just purchased a new set of tires for my car. This had the unfortunate consequence of making my wallet significantly lighter, which is bound to affect the weight balance of my vehicle. Luckily, my tire shop anticipated this problem, and based on the cost of the tires I chose, offered me a free alignment to help correct it. When the tech emerged with the alignment report, it reminded me that this might look like hieroglyphics to someone who didn’t know what an alignment was.
When we think of the wheels on a car, we imagine they’re like the rolling wheel in this video: Well-mannered and maintaining good contact with the road. But the truth is that cars are constantly subjected to stress, and are moving towards falling out of alignment. Once a car is out of alignment, the handling will be affected, tire wear will be accelerated, and the risk of a costly failure increases. This is why we created alignment one of 7 tire cheats that could save you serious money. So what does it mean to be in alignment? And what happens when your car isn’t properly aligned? Let’s dig in.
Camber is the angle of the wheel relative to a vertical line when viewed from the front or back. If the top of the tire is tipped in (towards the center of the car), it is known as negative camber. If the top of the tire is tipped out (away from the center of the car), it is known as positive camber. Camber is important because it can affect grip of the vehicle during cornering. A vehicle with negative camber will be resting on the inner shoulder of the tire when it is traveling in a straight line. When cornering, more of the tire will be in contact with the road surface. This is why most race cars will have negative camber setups. Positive camber can be used in vehicles that are anticipating a heavy load because the load will cause the camber to be more negative, which would result in a neutral driving position. Some modern cars use a slightly positive camber to reduce the force needed to steer at slow speeds.
No, this isn’t a misspelling of one half of the Gemini twins (or, for those who prefer topical references, anything to do with the Avox from The Hunger Games), this measurement has to do with the angle of the steering pivot points. If you look at a vehicle from the side, draw a line through the upper and lower pivots, and compare it to vertical, it will reveal the caster angle. Positive caster indicates a line that is tipped toward the rear of the car at that top (such as you can see in the motorcycle above). Negative is the reverse. Positive caster is a fairly common factory setting as it makes the vehicle more stable at speed and will effectively cause the tire to lean more while turning, which improves front-end responsiveness. The downside to positive caster is that it takes more effort to steer. With power steering systems, this issue is easily resolved.
Toe refers to the direction of the wheel when viewed from above. Alignment shops will set the steering wheel at a neutral position so that toe can be measured correctly. The easiest way to explain toe is to think of your feet. If you turn your toes in, you would have positive toe-in. Turn them out, you will have negative toe-out. The Jaguar above appears to have neutral toe settings. Front-wheel drive cars will tend to have a bias towards toe-out while rear-wheel drive cars will tend to bias towards toe-in. Toe can be used to affect vehicle dynamics, but it is most useful for preventing tire wear. If the toe is off by 1/16th of an inch, the tires will be dragged 1/4 of a mile SIDEWAYS for each 100 miles that you drive!
Cross Caster and Cross Camber
Many modern roads are crowned, which means that they are higher in the middle than on the shoulders. It is designed to help water flow to the side so that it doesn’t freeze or create standing water situations that can affect grip. If your car is setup with a neutral alignment, it will tend to pull towards the shoulder on a crowned road. Some manufacturers are specifying different camber and caster settings on each side of the car to account for this crowning. This setup, which usually involves slightly negative camber and slightly positive caster on the side of the car away from the centerline, is known as cross caster and cross camber.
Imagine drawing a line between the middle of the front and rear axles. This is known as the centerline. Now imagine a line that extends from the rear wheels. This line is known as the thrust line. If the thrust line and the centerline overlap, the thrust angle is zero. If they don’t, then the vehicle will tend to dog-track as it attempts to drive straight down the road. For vehicles with independent rear suspensions, the thrust line can be adjusted. If the rear is a solid axle, there is little that can be done other than attempting to compensate with the alignment of the front wheel, replacing broken parts, or going to a body-shop to straighten the frame.
Most shops will give you a printout that shows the conditions of the vehicle before and after the alignment, as well as how it compares to the manufacturer’s recommendation. If you’re a laid back driver, the standard settings will serve you well and will preserve your tires and suspension. Plan to rotate your tires regularly (roughly twice per year) and to get an alignment anytime you replace your tires or any suspension components. If you live in an area with lots of potholes, as I do, it can be a good idea to get more frequent alignments. Also, it’s worth getting an alignment if your tires wear unevenly.
If you’re a, let’s say spirited driver, you might want to request some different settings for your car. There are plenty of resources for this online. But keep in mind, this will accelerate your tire wear.
Like classics? It’s always Throwback Thursday somewhere.