Dandy. Ford has always had issues with poor suspension designs, but this car is a mess. It looks like the mechanic did the best he could with what he had to work with, but here's my observations:
LEFT FRONT - CAMBER -0.9 CASTER 4.4 TOE 0.02
CROSS CAMBER 0.0 CROSS CASTER -0.1 TOTAL TOE 0.02
RIGHT FRONT - CAMBER -0.9 CASTER 4.5 TOE 0.00
-0.9 degrees camber means they are tipped in on top a real lot. No alignment specialist, except possibly at a Ford dealership, could live with that. The right wheel is perfect for racing on an oval race track and making just left-hand turns. Both tires are running on the inner edges and that's where you will find the most wear taking place. The only thing good about front camber is both wheels are the same so their pulls will counteract each other. Remember though my comment about reading to the hundredth of a degree. You could have -0.94 on the left and -0.86 on the right. Both would be rounded off to -0.9 and appear equal, but in reality you have 0.08 degree pull to the right which is significant. With no more accuracy to look at, I'd like to see the left camber raised to -0.7 or -0.8 degrees. OR, ... The right could be lowered even more but I'd hate to make bad tire wear even worse.
Caster has no direct effect on tire wear and very little indirect effect. It also has almost no effect on pull on most front-wheel-drive cars. It does affect pull on rear-wheel-drive cars about half as much as camber does. Caster is easiest to visualize of you look at the fork of a bicycle or motorcycle. It goes forward as it goes down. That is positive caster which all cars use since the 1960s. It makes a more stable car to steer but it makes it harder to turn the steering wheel, so they added power steering to overcome it. Positive caster makes each wheel want to turn toward the center of the car. They balance out when you connect the steering linkage between them when they're equal, but on your car the right caster is 0.1 degree higher than on the left side so it is pulling to the left a little harder than the left wheel is pulling to the right. Again, with the less-accurate readings only to the tenth of a degree, it's impossible to know for sure, but 0.1 degree caster difference is not enough to overcome road crown. Without more accuracy, the two front wheels are too equal. If there is no other underlying cause, you will find the car pulls left when you're in the left lane of a two-lane highway.
The two toe readings are not equal which at first glance would say the steering wheel is off-center, but the difference is REAL small. Too small to be noticed, and it can easily be due to normal play in the steering system. Alignment computers can be set to read toe in inches or in degrees. At the moment I can't remember which is which but one method turns out to be exactly double the other. As I recall, I believe 0.06 inches equals 0.12 degrees. I'm accustomed to using inches, and 0.06" is 1/16". That's a typical setting for a front-wheel-drive car. It means the fronts of the tires are 1/16" closer together than the rears of those tires. The goal is that road forces pull the tires back and make them perfectly parallel for best tire wear. Rear-wheel-drive cars which don't have the engines tugging the tires forward usually call for 1/8" toe-in to make up for road and braking forces.
With only 0.02 inches or less toe-in, your wheels are starting out almost parallel already, then when you add in road forces, they are going to pull outward in the front and both will be steering away from the center of the car. Since the car can't follow two tires going in two different directions, it has to pick one, and that one will be the tire with the most weight on it. Usually that's the right tire. Since roads lean to the right, so does the car, and that puts more weight on the right tire.
Besides the pulling problem, not enough toe-in will cause accelerated wear to the inside edges of both tires. Imagine holding a pencil straight up with the eraser down. Set it on a table, push down on it, then slide it sideways across the table. The leading edge of the eraser will make eraser crumbs and wear down, but the trailing edge will bend up and no wear will take place on that part. The same thing happens on your tires. First you have to understand what is meant by the "leading edge" of the tire. Your tires are too far apart at the front. When you add in road and braking forces, both tires turn out more. The right tire is turned a fuzz too much to the right. Imagine it is turned more to the right, ... And more, ... And more, until it is turned 90 degrees. That's twice as far as you can actually do with the steering wheel. NOW you can see that the inside sidewall and edge of the tread is in front and is the first edge of the tread to come down the road. The inner edge is the "leading" edge. Okay, it's not nearly that severe, but as with the pencil eraser, those leading edges on both tires are what is going to scrub off on the road while the trailing edges will tend to lift up and not wear so much.
Excessive camber only affects the wear on that one tire, (although in your case camber is off on both tires). Incorrect total toe always affects both tires equally In your case, Ford gave you excessive negative camber on both front wheels and the mechanic gave you insufficient total toe-in. Both of those will cause accelerated wear on the inner edges of both front tires. I should qualify that by saying I left my job as an alignment specialist to go into teaching in 1999. At that time there were a few cars and full-size vans starting to show up that DID call for only 1/32" total toe-in, and they did achieve decent tire wear. Before you tell your mechanic I said he has total toe set wrong, find out what the specs call for. He might have it set right according to the book, but setting it to a little more toe-in might reduce the tendency to pull right.
LEFT REAR - CAMBER -1.2 TOE 0.08
TOTAL TOE 0.16 THRUST ANGLE 0.00
RIGHT REAR - CAMBER -1.6 TOE 0.09
My next point of concern is the rear camber. You should be able to stand behind the car and see the right wheel tipped in on top. 1.6 degrees is a pile. That's how the older Escorts and Tempos came, but we had kits available to help correct Ford's terrible design. Your mechanic made reference to an adjuster that can be installed to correct that. I'd get that done. At least it will reduce the wear on the inner edge of that tire. It may reduce the pull to the right too. Normally rear camber has such a small effect on pulling that we ignore it, but when you're looking for the elusive cause of a pull and you have something so severe staring you in the face, it IS possible it is related when it's this bad. Negative 1.6 degrees means the tire is tipped in a lot on top. That will make it want to pull to the left. It will normally just follow the car but when it's so high, it can make the back of the car go to the left which would turn the car to the right.
Related to that, here are some generalizations that can sometimes provide clues. When you let go of the steering wheel and it turns to the right by itself and the car goes to the right, it is usually caster-related. Caster numbers refer to when the wheels are pointed straight ahead. The amounts change, (but can't be measured), when you turn. One side goes up and the other side goes down. After you turn a corner and the two sides are different, they want to come back to where they're exactly equal. That's what makes the steering wheel return to center by itself. While driving down the road, if caster is not equal on both sides, the steering system will want to turn until they ARE equal and balanced out. You see that by the steering wheel turning a little when you let go of it.
When you have a pull related to unequal camber, the steering wheel will stay perfectly straight when you let go of it, but the car will go off to the side. This can be confusing because you have to turn the steering wheel the other way to counteract that pull. Tire pulls will also not cause the steering wheel to turn
If the rear tire is steering the car to one side, you will also not see the steering wheel turn when you let go of it. These are generalizations, and they all assume everything else is equal side-to-side and correct. When multiple things are wrong, it's hard to know how the car or the steering wheel will react.
Another thing you have to be aware of is how the manufacturer determines their preferred alignment settings. A common spec. That I'm very familiar with for front camber is 0.50 degrees plus or minus 0.50 degrees. That means anything between 0.00 and 1.00 is acceptable. In reality, either of those two extremes would result in accelerated tire wear over time and no alignment specialist would set them there. All those numbers mean is if the alignment is checked while that vehicle is under warranty, they are close enough and the manufacturer will pay for the alignment check, but not to have any adjustments made. This reduces the number of alignments they are obligated to pay for. When it comes to taking your money for an alignment, we normally want to give you the best service possible. To do that, every alignment computer has a "reduce tolerance" button that will shorten the range of acceptable numbers forcing us to set each wheel closer to "perfect". Instead of 0.50 degrees plus or minus 0.50 degrees, it will read 0.50 degrees plus or minus 0.15 degrees. We don't get so much leeway now. We have to be more precise. Your mechanic may have not pressed the "reduce tolerance" button because we become accustomed to what settings are in your best interest without needing the machine to tell us. That button becomes more valuable when we want to show you on the printout why we needed to do something for you. Once we reduce the tolerance and a number is out-of-specs, there will be a message to that affect on the printout. People believe printed messages more than they believe their mechanics.
The last thing has to do with the tire pull. Seems the cause of the pull has been identified. Switch those two tires side-to-side. There's a small chance the car will still pull the same way. If it does, switch them front-to-rear. I'm surprised the mechanic didn't switch them while he had them off the car.
1) Switch the right front tire.
2) Have the adjustment installed to raise right rear camber to less negative.
3) Ideally, raise left front camber from negative 0.9 to negative 0.7 degrees.** Less ideally, increase right front caster to make that wheel pull harder to the left, or lower left front caster to make that one pull less hard to the right.
4) Measure ride height and compare to specs. Sagged springs result in increased tire wear even when the car appears to be in perfect alignment. They don't cause a pull unless they are sagged unevenly.
5) Increase the amount of toe on each wheel by 0.02 inches unless it is at specs right now. That will bring total toe to 0.06 inches which closer to the 0.12 inches most cars use.
** Car models vary a lot in how much affect any alignment setting has on pulls and tire wear, and they vary a lot on how much unequal caster and camber settings can offset each other. I don't have a good feel for this car model in particular. One more thing you can look at is to see if they list the same caster and camber specs for both sides in front. If they do, which is most common, they are leaving it up to the mechanic how much left-hand pull to adjust in to offset road crown. Ford often gives two different specs for the left and right side indicating they know how much side-to-side difference is needed. In that case, it can be possible to set both wheels the same and have them be in specs but not be correct. When they specify a setting to create a left-hand pull, the car needs that.
Tuesday, February 5th, 2013 AT 3:05 AM