Maintenance – Suspension Alignment
Wheel alignment is adjusting the wheels to point straight ahead (toe), not to lean to either side (camber), and to maintain stability (caster). Some adjustments can be made using adjusters built into the car. Other adjustments are made by inserting or removing shims between the frame and suspension components. On many cars, there is no way to adjust caster or camber, and when an alignment angle is found to be out of specification, other steps must be taken. One possibility is loosening suspension bolts, prying the component in the desired direction, then tightening the bolts. Another possibility is the use of aftermarket shims or adjusters to add adjustability. If none of these options will work, whatever component or components are bent must be replaced.
Wheel alignment can be measured in a number of ways. Solutions such as string (just like in your kitchen drawer) and bubble gauges(sort of like a level) can be used (in fact that’s how they taught it when I was in school), but most shops are using laser or photo equipment these days. We use are using a Hunter DSP600 for our alignments. It offers the fastest setup and most accurate measurement of any system we investigated. It was also the most expensive, but with the time saved during the alignment setup, we will eventually recoup the extra cost while providing our customers with very accurate alignments.
You will find many tire stores that recommend aligning your car every 6 months. I our opinion this is a waste of money unless you own some seriously exotic and expensive tires. Let’s say your tires are $400 for a set of 4 with mounting, balancing, stems, weights, disposal, tax and any other stuff you need. A pretty average price for a small import car. Let’s also say you bought a pretty average tire with and UTQG rating of 420AB and your are a pretty average driver who drives a 50/50 mix of freeway and around town for 12,000 miles every year. You might expect 30,000 miles out of the tires with proper air pressure, moderate driving and road conditions, a 7,500 mile rotation and balance schedule, and perfect alignment. If you were to align the car every 6 months, that would mean 5 alignments during the life of the tires. 5 x $92 per alignment would be $460 spent on alignments. So for this scenario you’ve spent $860 for tires over 3 years (not including rotation and balance). Now let’s imagine your car is out of alignment and it’s wearing out tires twice as fast as it would if it were in alignment. You once again spend $400 on tires, but this time the tires wear out after a year and a half and you have to buy another set for $400 to make it to the 3 year mark. In this scenario you’ve spent $800 for tires over 3 years, and saved $60.
I should mention that a lot of “economy” Japanese cars are starting to come with extremely expensive low profile tires, and $1000 tire replacements are not that uncommon these days so my hypothetical may not apply to you. That being said…
Should you get your car aligned when it needs it? YES! Should you get your car aligned on some sort of schedule? No. Should you freak out when your tires wear out a few thousand miles before they might of if you had followed some sort of obsessive alignment checking routine. Absolutely not.
Here’s our alignment recommendations: If the car pulls, align it. If the tires show significant irregular tire wear, align it. And if for some strange reason you feel like you want to help us pay off our ultra high tech $40,000 alignment machine, you are welcome to come in for daily alignments 🙂
Here’s some information on alignment angles
Toe, simply put, is direction the wheels are pointing. Zero toe would be perfectly parallel wheels pointing straight forward. Toe-out means the front of the tires are farther apart than the rear of the tires. Toe-in means the front of the tires are closer together than the rear of the tires. Toe has different effects on tire wear in the front and in the rear. When the front wheels are toed out, the inside edge of the tire scuff and wear out early. When the front wheels are toed in, the outside edge will scuff and wear out early. However, on rear tires toe usually causes a diagonal cupping wear pattern whether the tires have too much toe in or too much toe out. The diagonal cups are caused by the tires hopping and skipping along the road. It’s hard to explain why, but I’ll give it a try. Draw an overview of a car with 4 wheels on a piece of paper, make the front wheels parallel, but toe the rear wheels in substantially (say 45 deg. in just to make the demo easier) Now draw lines parallel with the rear tires following their path of travel if they were to roll. You will notice that the lines you have drawn intersect. Since the tires are attached to the car they can not intersect. Instead they roll a bit, then skid outward, roll a bit, then skid outward again. This goes on and on until the tires have diagonal cups worn into the treads where they have been skidding outward.
Camber is the lean of the wheel. If the top of the wheel tilted away from the car, that is called positive camber. If the top of the wheel is tilted in towards the car, that is called negative camber. Camber can cause a pull to one side or the other depending on the direction of the lean. The car will pull in the direction of the wheel with the most positive camber. However, if both sides have the same amount of negative or positive camber, they will cancel each other out and the car will not pull. Camber can cause premature tire wear, but is not as hard on tires as toe is.
Caster is the hardest to explain of the three commonly adjusted alignment angles. I like to use the motorcycle analogy. Lots of positive caster is like the forks on a chopper; the wheel is far in front of the support for the wheel. No car that I know of uses negative caster, so I’ll describe less positive caster as like the forks on a regular street bike, the wheel is only slightly in front of the support for the wheel. Caster will not affect tire wear, but it can cause a slight drift if it’s not equal on both sides. Caster is an angle that only applies to the front (steering) wheels of a car. The more positive caster is, the more stable the car feels, especially at higher speed. More positive caster also improves steering wheel return. To help understand what steering wheel return is, try this experiment: next time you turn a corner, let go of the steering wheel when you are done turning. You will notice that the steering wheel spins back to the centered position. Without positive caster, the steering wheel would stay turned until you manually turned it back to the center position. The only downside to lots of positive caster is it make the car hard/slow to steer. The reason positive caster adds stability, steering wheel return and increased steering effort is the weight of the car is trying to straighten the wheels. You may notice on some luxury cars with lot of positive caster (and powerful power steering) that the front of the car will rise when the wheel is turned to the side, and sinks as the wheel comes back to center.
The thrust angle is the direction the rear tires are pointing in relation to the center of the car.
Toe Out on Turns
Toe out on turns is a measurement that is used to check for a bent steering arm on the knuckle. Toe out on turns will cause premature tire wear, and can sometimes be the source of unexplained premature tire wear on a “perfectly aligned car” since it is not normally checked during a standard alignment. It also can cause excessive tire squealing when cornering. When the car is driving in a circle, the outer front tire will be traveling in a larger circle than the inner front tire, it therefore will need to be held at a slightly shallower angle to roll without scuffing. This difference in angles is built into steering arm on the knuckle. There is no adjustment for toe out on turns. If there’s a problem the knuckle must be replaced. When toe out on turns is off, there is almost always a collision the the car’s past.
The included angle is a diagnostic angle, like toe out on turns. It is calculated using the camber measurement and the SAI measurement. The included angle is built into the design of the car and is not meant to be adjusted. When we suspect there may be some bent parts, we check that the included angle is equal side to side. If not, there’s likely a bent knuckle or strut.
This is another diagnostic angle. It’s basically the distance between the front and rear tires. When set back is off and other angles are OK, the body / frame of the car usually needs to be repaired or straightened.