LONG w/ Details. . . .
H,
The original numbers say the car should desire going left into traffic (BAD!) and wear the insides of all four tires (front more so) until that alignment.
Here's a snap shot of what some of that means.
Camber:
Camber is the vertical tilt of the tires in and out at the top. In at the top is (-). Out at the top is (+). Camber can make a care pull. Take a dixie cup and place it on the table. Its a tappered cup, place the large opening to torwards your right hand and pretend its the left front. Roll it. It goes left in circles. That's the negative camber pulling the car left. Tire width and wheel offset affects how much a car may want to pull when the two sides are not within a 1/4 to 1/2 degree of each other.
Caster:
The lean for and aft of the hub relative to its axis (strut/ball joint), the inclination created between the relationship of the upper pivot (strut mount) and the lower pivot (lower ball joint). A motorcycle fork has positve caster while a shopping cart wheel has negative caster. Your car with near equal caster implies the angle from the top of the strut to the lower ball joint is the same from side to side which implies there is little setback on the left front. The curb issue didn't push the wheel back or the caster would go down in value towards 0.
The print doesn't list setback so picture this: A perfect "T" has no setback (picture the tires are the ends of the cross (X). Both outer points are 90 degrees from the vertical line. If a car is curbed hard enough, the wheel can bend things back. Most likely to go are the ball joint itself, the lower a-arm, the sub-frame where the a-arm mounts, or the whole sub-frame moves back! This is one way to loose caster. Sometimes the strut shaft bends and as you travel down the road it rotates a little and you have variable toe, caster, and camber.
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You're final numbers with -0.8 camber can result in some inner tire wear at all four corners, but it should drive well into the corners. Ever notice those early Ford Focus's (early 80's). They were built with like +1.5 camber (tires tipped out at the top) front and -1.5 in the rear. The result is a car that pushes into the corners and forces the driver to back out of the gas. Postive camber in the front leads to pushing as the tires scuff easier while the negative in the back grip and hold. The result is simply not comfortable to drive at speed. Yours being nearly matched isn't a bad thing except for tire wear on the insides.
How about torque steer? At cruise with a steady throttle, which way does it go? Under acceleration it goes right, deceleration goes left. A parts wear and rubber softens and the lower control arms move more. This is where the preset Toe in can play a role. Ideal toe in the front is like Zero degrees (less rolling resistance and better tire life). But these are front wheel drives with the steering rack behind the axel. When you stand on the gas the wheels pull the lower A-arm forward and change the toe, creating a "Toe out" condition. This makes them want to dart from side to side but mainly right due to torque. Adding a little toe-in can help mask this, but don't add too much or tire wear becomes a tire wear issue.
Thrust line; We've all driven a car with the steering wheel down on one side while going straight. These cars can have a perfect alignment with zero toe and still have a crooked steering wheel while going straight. To simplify; this is the thrust line and its off on these cars. That is a zero thrust line should equate to the wheels being pointed straight ahead (front or back).
But if we move to the rear of the car and dork up the thrust line there (shift the toe on both rear wheels to the left for example) now we see the car go down the road sideways (crab walk) with the drivers side of the car being seen just as much as the bumper when following it. All these are good signs of cars with damage from something or really bad alignments.
Toe;
For best tire life, zero toe front and rear is good. "Toe-IN" causes wear on the outsides of the tires (assume Zero camber). "Toe-OUT", will cause wear on the inside edges. However you can offset some of this by varying the camber too.
Repairs:
When people drop the subframes on these front wheel drives, what types of things can happen to the alignment?
Lets say the sub-frame its perfectly aligned left and right but shifted straight forward; This increases caster and toe out.
Straight back; decrease caster, reduces toe.
Shift the subframe Forward on the right front and backwards on the left front: LF caster goes (-), RF goes caster (+), toe ??, driving = pulls left as higher caster numbers push the opposite direction. hehe Keep an eye on those tranny guys!
Rule of thumb:
Areas with lots of crowned roads, may have cars set up with less caster on the left than the right to make the car drive straight on crowned roads.
Ever notice luxury car like the M-Benz? Lots of + caster makes them drive nice up on an open highway as caster makes the car want to go straight. A car with Zero caster would be miserable and scary as caster is what makes the steering wheel return to center after completing a corner.
I could blab about this for a while and might just pick up an write that artcle on wheel alignment one day.
As for your car at speed and being unstable; its likely a combination of worn out parts, tires brand and tire pressure. If the rack mounts, tie-rod ends or rack itself have freeplay, the grooves and wind will move you about. Couple that with tires that don't work well for your car and you have your hands full.
Let me just say that I've had some cheap 78 series tires on a car and it drove better with them than a bad set of 50 series tires (different rim of course). Some sidewall designs just don't do well on all cars. Usually it can be masked by getting the tire pressure just right on the front and rear and I seperate the two as typically they are not the same number (psi).
I hope this length of blabage was helpful to someone. . . :ugh3:
