Can I improve the handling by changing the wheel alignment?

Altering the wheel alignment to improve the handling is probably the simplest, most dramatic improvement you can make to any car for the cost involved. First though what is wheel alignment and what do all those terms mean?

Toe
Toe describes the angle at which a wheel sits on a horizontal plane relative to the longitudinal axis of the car. In other words imagine looking vertically down on top of a wheel mounted on a car, if the front of the wheel is angled inwards more than the rear of the wheel then it is said to have ‘toe-in’, if it’s the other way around then the wheel is said to have ‘toe-out’. If the wheel is parallel with the longitudinal axis of the car then it has zero toe. Toe can be measured in degrees but more commonly, it’s measured as the distance difference between the front of the wheel rim and the rear of the wheel rim. Total Toe is the overall distance for a pair of wheels whereas Individual Toe is half the Total Toe and relates to individual wheels. Toe-in increases lateral stability but can lead to wear on the inside shoulder of the tyre. Front end toe-in dampens turn in response but improves the self centring action of the steering while rear toe-in helps to reduce oversteer due to the improvement in lateral stability. Toe-out reduces lateral stability and can lead to wear on the outside shoulder of the tyre. Front end toe-out can improve turn-in response while rear end toe-out encourages oversteer due to the reduction in lateral stability. Toe can be altered on the front by adjusting the track-rod ends and on the rear by adjusting the toe control arms.

Camber Angle
Camber describes the angle at which a wheel sits in a vertical plane. Imagine looking at the wheels as you stand in front of the car. If the top of the wheel is angled inwards, towards the car then the wheel has negative camber, similarily if the top of the wheel is angled out, away from the car then the wheel has positive camber. If the wheel sits vertically then it has zero camber. Camber is measured in degrees. The ideal contact patch of the tyre onto the road would logically be with the wheel in the dead vertical position (zero camber) so why are most performance cars set-up with negative camber? To understand why negative camber is good for performance you have to imagine how a car behaves during a corner. With a car set-up with the wheels with zero camber as soon as you enter a corner the wheel on the outside of the bend (the one that provides the most driving force) will roll over slightly due to the cornering forces, the body will also roll over. The tyre on this wheel will no longer have the ideal contact patch on the road, meaning the cornering performance is reduced. Now if you set the car up with negative camber, when it enters the corner the wheel and body will still roll over but this time, if set-up correctly, the wheel will roll over to near zero camber. This means the tyre contact patch is much better, so cornering performance will improve. So static* negative camber is used to compensate for body roll, body distortion and tyre roll when cornering. The downside to all this though is that having the car set-up with large negative camber means the tyres can wear on the inside edges when driven in a straight line continually. Setting up the camber is matter of balancing out the performance gains during cornering with the tyre wear effects on the straights. *Static means with the vehicle stationary and under no load.

Castor Angle
Castor Angle is the angle to the vertical plane on which the steering axis sits as viewed from the side. In other words imagine looking at the side of the front wheel, the Castor Angle is the angle an imaginary line makes that is drawn through the centre of top ball joint (or top mount of a Macpherson strut) and down through the lower suspension arm ball joint. Looking on the diagram, if you follow the Castor Angle line down you can see it hits the ground in front of where the tyres contact with the ground, this is Positive Castor. This means the tyres will always follow the steering input or in other words act just like a normal furniture castor wheel. Castor Angle determines the amount of self-centring the steering will have, influence the straight-line running and with the Kingpin Angle it will influence the camber change when cornering as a function of the steering input. Castor Angle traditionally used to be very small as large amounts of Castor Angle created heavy steering, now most cars have power steering this is not such a problem. Large Castor Angles mean greater, dynamic** camber changes can be created and that means better negative camber when cornering and smaller camber on the straight, ideal for both performance and wear of the tyres unfortunately too large a castor angle can lead to poor turn-in. **Dynamic means with the vehicle moving and under load.

Kingpin Angle, Kingpin Inclination (KPI) or Swivel-Axis Inclination (SAI)
This is much like Castor Angle, in fact it is exactly the same imaginary line through the centre of the top ball joint (or top mount of a Macpherson strut) and down through the centre of the lower ball joint except Kingpin Angle is the angle this line makes to the vertical as viewed from the front of the car and not the side. The Kingpin angle is set to try and get the pivot point as close to the tyres contact point on the road as possible (generally). This is done as otherwise the wheel will ‘scrub’ on ground when turned as the pivot is off centre. The distance between the point where the Kingpin Angle hits the ground and where the tyre meets the ground is called the ‘Kingpin Offset’ or ‘Scrub Radius’. A positive Scrub Radius or Kingpin Offset is when the Kingpin Angle hits the road surface on the inside of the centre line of the tyre contact point (see the diagram below), a negative Scrub Radius is when the Kingpin Angle hits the road on the outside of the centre line of the tyre contact point. The Kingpin Angle, along with the Castor, dictates the self-centring action of the steering and the affect the steering will have under braking. Fitting larger wheels can alter the Scrub Radius if the correct offset is not chosen which in turn can affect the handling.

So what do I set the Geometry too?
Actually there is no real answer to this as one persons preference maybe completely the opposite to someone elses. For example if someone tells you to run with 2 degrees of negative camber on the front without asking you how you drive or on what roads then they may just be condemning your tyres to an early grave if you mainly do motorway miles! The only advice really is to start with the factory settings, run for a while with those and then tweak it here and there until you get the right balance for you. For the Evo’s the only adjustable items are the Front and Rear Toe and Front and Rear Camber (camber to a lesser degree on the earlier Evo’s). Castor and Kingpin angle are only adjustable very slightly or not adjustable at all. Castor and Camber can be adjusted if an aftermarket kit is fitted.