I frequently get pm's/emails w/ ?'s on alignment so I thought I'd put together a a alignment basics thread. We'll look at camber/caster/toe, do's and don't for alignments and a few other bits and pieces along the way.
Camber- what is it: measurement in degrees of the tire/wheel from the front
What does it do for us- negative static (car not moving) camber can help us gain grip in turns, when our cars turn the outside tire wants to go positive, by having neg camber this positive change is negated and we optimally get a flat, wide contact patch.
Excessive neg camber can degrade straightline braking (less contact patch) and can cause excessive tire wear (not as much as you'd think though- ore on that w/ toe).
The oe spec for front camber on the WRX is -0.25- that's not a lot, especially for a performance orientated car. The WRX's upper strut bolt is eccentric and allows for adj, w/ the stock bolt- it's common to be able to get close to -1.4 degrees w/ the oem bolt. Camber plates (or caster camber plates) can increase this to close to -2.5 - -3.0. Some have also combined a camber bolt in the lower hole w/ the oem bolt to increase camber.
The oem spec for rear camber is -1.3, there is no adjustment in the rear oem, many use camber bolts in the rear to provide adjustment.
The oem specs provide for limited performance and help promote understeer- by increasing front neg camber you dial out some understeer, by adding positive camber to the rear you do the same. With camber bolts in the rear you can add some positive camber and dial out some understeer- you don't want to dial out too much though as you still want static neg camber for improved grip in corners.
Cross camber- the difference between left and right camber settings, you want this as close to zero as possible.
what is it: Caster is the angle of the steering pivot, measured in degrees, when viewed from the side of the vehicle
Caster also expresed in degrees, can help w/ performance as it goes more positive (ALK or caster/camber plate) it has the same effect as adding static negative camber. It also provides for straight line stability. It is not adj oem.
The oe specs for the WRX are ~ 3.5 degrees, the ALK adds ~ .5 degrees, caster/camber plates ~ to 1.5 degrees.
Most feel there are no negatives to increased positive caster (a little heavier steering effort), some cars run w/ as much 8 degrees.
With caster plates you are able to control cross caster as well.
what is it: The toe measurement is the difference in the distance between the front of the tires and the back of the tires
this example shows toe in
Toe is adjustable both front and rear, the oem specs are 0 (+/- 3mm)- toe is adjusted in the front via the tie rods in the rear via the rear lateral links.
Toe contributes more to tire wear than camber, thus most reccomend near 0 toe. Toe can also effect performance, toe out in front will help w/ turn in, toe out in the rear w/ rotation, toe in front and rear w/ high speed stability. People play w/ toe for performance gains, but make sure you know what you are doing befoer considering something other than very near 0 toe.
Cross toe is important as well, again as close to 0 as possible.
Alignment do's and dont's
-do request a before and after printout
-do tell them you want cross toe and camber as close to 0 as possible!
-it's better to give them specific specs vs just getting it to "spec"- spec can range from positive camber on one side to neg on the other, toe in one side- toe out on the other- the factory specs are pretty wide (too wide!)
-some shops won't do "custom" alignments- know that before going in
-if your shop is having trouble getting front neg camber approaching -1.0+ tell them the lower strut bolt needs to be loosened as well to achieve this- you won't belive the # of shops that don't know this
These are basics, I reccomend to everyone to learn more- your alignment is one of the biggest contributors (ditractors) of suspenion performance.
WARNING this has not been thoroughly proofed, if there are glaring errors please let me know- thanks.
Here are the oem specs