Let's Get Technical: Alignment

By Tom Dobush, November 2013

Previously I touched on tires and suspension and how they work together. In this article I will go into more detail regarding the alignment of the suspension and tires. As I mentioned before a healthy and properly aligned suspension is crucial to driving safety, as well as economy and performance. There are four main suspension angles that come into play and require adjustment from time to time. They are camber, toe, caster and thrust angles. How frequently adjustment or realignment is needed depends greatly upon your vehicle, your driving style and the roads you drive on.

The most common reason for needing an alignment is uneven and/or premature tire wear. Since the tires are the most important part of your car, I hope we can agree that their health and wear is something that should be paid close attention to. Unfortunately, tire wear is something that happens fairly gradually over a long period of time, so changes in their health can be very subtle. It is best to have an expert “read” or check your tire wear often, as in once a month if possible. It only takes a few minutes and can save you money and increase your safety in the long run.

Let’s say, for example, you or your mechanic notice the inside or outside edge of any of your tires are wearing faster than the rest of the tire. This is most often caused by a camber issue. Camber angle is the tilt of the tire inward or outward in the vertical. If you are standing at the front of your car looking back at it, the distance between the tops of the tires is usually shorter than the distance between the bottoms. Imagine each tire, in an exaggerated case, as the sides of the letter “A”. The amount of camber effects cornering greatly by determining how much of your outside tires make significant contact with the road as you make your way around a turn. While this can help handling, too much camber can wear the inside edges of your tires before the rest of the tire and create road “wander”, where your car follows grooves and cracks in the road. Conversely, too little camber and your car may not want to turn in crisply (or at all) or may be unstable mid corner, and the outside edges of your tires will wear out too soon. The proper amount of camber angle is determined by a factory specification for road use. Obviously, these specs can be pushed to extremes when setting up a car for enthusiast, performance or track driving. The difference in camber angle between the right and left side is called cross camber. Basically, the cross camber should be as close to zero as possible or the left and right side cambers should be equal and opposite for most applications otherwise your car may pull or drift to one side or another, like and italicized “A”.

Now, let’s say your mechanic mentions your tires are “cupping” or “feathering” or perhaps you notice excessive rotational vibration or road noise, often reminiscent of a buzz or hum. This can be caused by a tire being out of balance and wobbling as it spins, causing uneven wear. More often this cupping is the result of the toe angle in one or more corners of your car being out of spec. Toe is the angle which the tires are pointed in the horizontal. Imagine as you sit in the drivers’ seat, either your front or rear tires can be pointing in or out. Toe in means the fronts of the tires are closer together than the rears of the tires. An exaggerated example would be to again think of the letter “A”, but this time as you imagine looking down at your car from above, with the front of the car towards the top of the page. Toe out is just the opposite, like the letter “V”. Toe angle can be adjusted either way for desired effect. This depends on each cars engine and drive train layout, and of course there are factory specs and more aggressive set ups. Too much toe in usually causes cupping or just general premature tire wear. Same can be said for too much toe out, as well as the car having excessive drift or road wander again. Toe is the most important angle in regards to premature tire wear. Similar to camber, the left and right sides should be equal and opposite in angle to keep the car tracking in a straight line. In fact, if all your tires pointed perfectly straight ahead, you would have zero toe angle and your car would be very hard to control.

The next angle to think about is caster. This is the tilt of the steering axis towards the front or back of your car. Most important is your cross caster, or the difference in caster angle from left to right. Again we want this to be as close to zero as possible, both sides being even so neither pulls more dominantly over the other, keeping the car traveling in a steady straight line when the steering wheel is pointed straight. Too much cross caster and your car will pull or drift  in one direction.

Finally, we have the thrust angle. This is the path of the rear axle compared to the centerline of the vehicle. We want this angle to point straight forward as much as possible. Sometimes the slightest waiver of thrust angle is impossible to eliminate and therefore the other suspension alignment angles must be adjusted accordingly to counter act the effect.

So now you have a basic idea of what a proper alignment consists of. Suspension alignment has a huge effect on tire life, handling, fuel mileage and suspension parts wear. Also proper alignment makes your car a lot more fun and safe to drive! And after reading all this, please do not neglect to check your tire pressures!!

I would like to know if you have found my articles worthwhile and informative or if I am off base, either over the top or dumbing things down, so please send me some feedback, good, bad or indifferent. J I will greatly appreciate it, as well as any questions for further topics on literally anything BMW, automotive or driving related. Please drop me a line at BavarianRocketScience@gmail.com and thanks for reading. Be safe and happy motoring!