A Poor Alignment Will Cut A Decent Set Of Tires Lifespan In Half, But It Will Also Make A Good And Otherwise Well-Handling Car Turn Like Crap.
Dismissing everything else and chocking up the AWD platform as the answer to automotive invincibility is easy. With all four wheels getting work done, lesser drivers can surely bend the laws of physics, pulling off maneuvers that would otherwise send less-equipped vehicles to their metal crunching end. But this just isn't the case. Although AWD can prove to be an asset in regards to safety and cornering, the fact that your all-mighty EVO or brute of an STi has more in common with a FWD econobox than practically anything else when it comes to chassis setup just might surprise you.
Why, you ask with that touch of dismay. The answer is that most AWD cars share one major thing in common with the typical FF (front-engine, front-wheel drive) sedan - most of the weight is over the front wheels, distributing out percentage-wise to at least 60/40. Even the Skyline GT-R is saddled with such tonnage over its front wheels. Most AWD cars like the DSM triplets, the EVO, the Audi Quattros and the WRX/STi, share most of their chassis components and drivetrain layouts with their FWD counterparts. Transfer cases and other bits of AWD hardware add additional weight over the front wheels. For example, the GT-R has the heavy iron-block RB26DETT up front and a drivetrain that weighs a figurative ton. Because of this, many chassis settings used to make AWD cars stick are similar to those of a well set up FF car.
Robert Fuller of Robispec once summed things up pretty well: "Most AWD cars are really FWD cars except they come off the corners better." There are exceptions though. The Porsche Carrera and the Skyline GT-R behave more like RWD cars but for different reasons; most of the Porsche's weight is over the rear wheels and the GT-R's ATTESSA torque biasing system attempts to shift as much torque to the back of the car as possible. Thus a GT-R behaves more like a FR (front-engine rear-wheel drive) sports car and requires a somewhat different setup. The EVO, Audi A4 and S4 Quattro have aftermarket center differentials that distribute a larger percentage of torque (60-70 percent) to the rear wheels. The STi has a center differential with an adjustable torque split able to supply up to 70 percent of torque rearward when adjusted accordingly. These vehicles also behave more like the GT-R.
Before attempting an alignment, there has to be something to actually adjust. Eccentric cam bolts and camber plates can be used to adjust alignment settings on vehicles equipped with MacPherson strut suspensions. Multi-link suspension vehicles use adjustable ball joints and various links for adjustability.
There are two reasons you'll do an alignment: because you have to or because you know you should. A poor alignment will cut a decent set of tires' lifespan in half, but it will also make a good and otherwise well-handling car turn like crap. Either way, measurements like camber, caster and toe need to be set up properly, whether the goal is prepping a Time Attack car that won't lose or just preserving a cheap set of radials from Wal-Mart. The terminology's the same and the procedures are similar, but alignment settings when concerning an AWD car vs. front- and rear-wheel drive cars are slightly different.
Before going any further, it's assumed that those reading are interested in getting the most out of their suspension, not maximizing tire wear or something weenie like that.
Make it Adjustable:
Chassis adjustability is an important element when searching for grip but is often the most ignored. Sexy, adjustable coilovers and big anti-rollbars get a lot of attention, but being able to adjust camber, caster and toe are just as critical and usually ignored by most enthusiasts. Most of the cars we're talking about are only adjustable for toe or have very limited camber adjustability. So before you start, make sure your car is equipped with camber plates and adjustable links.