Tech Talk FAQ - Wheel Alignment Terms & Theory

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Alignment

What are the best settings?

Camber

What is it?

Caster

Dynamic & static

What are you talking about?

Toe-in or toe-out

Alignment settings - What are the best ones?

The simple answer is that there is no such thing! 

I know we have probably given more information here than most people wanted, but even this only scratches the surface of the available information and variables that need to be considered when contemplating optimum wheel alignment settings.

The most important thing and something we can not stress enough is the fact that alignment settings are NOT an "absolute truth" that can be held up as an undisputed rule. It is a dynamic process with the "correct value" varying from driver to driver, car to car not to mention the driving environment.

If you think of wheel alignment geometry as a means by which to pre-empt dynamic changes to the tyres attitude it will be a lot easier to understand what is appropriate. Though a very simplistic definition, it helps us understand that maximising tyre contact while driving and cornering is the object of the whole exercise. So, in deciding an optimum static alignment angle we strive to make predictions as to what angle the tyre will take under various dynamic conditions so we can pre-empt these changes.

For example, we use some negative camber on the front to pre-empt body roll while cornering which will tend to tilt the tyre towards the vertical. Having lots of negative camber on a drag car would be fairly pointless as cornering is not an issue but traction is, hence the amount of negative camber on a general purpose vehicle is often a trade off between conflicting functions.

One of the only measures of success in evaluating the "correct" angles is to use a pyrometer to measure tyre temperatures across the face of the tyre after use. This and a good physical examination of the tyre will reveal many things and will ultimately determine the accuracy of your predictions.

Whiteline has no agenda in publishing it's alignment settings or recommendations as part of it's suspension packages. It is not copyright property that we profit from. It is done to help people get the most out of our products and their cars. These settings are the result of a lot of time and effort on our behalf and represent an optimum starting point for enthusiastic driving though we strongly encourage people to then monitor tyre wear and balance to fine tune the absolute numbers for individual circumstances.

Bottom line, just follow our recommendations to start with and fine tune later. It won't cost you a cent and it will save you a lot of initial headaches. You've got nothing to loose.

Camber – What is it?

Camber is the inclination of the wheel from the vertical when viewed from the front. When the top of the wheel leans out you have positive camber, lean in equal’s negative camber.

Static negative camber is used to compensate for body roll, body distortion and tyre roll under when cornering. Stiffer bodies and tyre sidewalls are in and unnecessary suspension compliance is out. Therefore the previous requirements for large amounts of static negative camber are disappearing. Whiteline strut braces are good for maintaining camber angles under cornering loads as they further minimise body flex.

Its important to highlight the fact that camber settings are ultimately a personal thing. That is, Whiteline can provide an indicative range to start from but the final number will depend on your driving style, average driving conditions, tyre size and many other things. You need to start with a relevant number, then monitor tyre wear and compensate if necessary.

Whiteline have a range of camber adjusting products available to achieve the optimum settings. This includes eccentric camber bolts, dual angle shims and Commodore adjustable strut tops.

Caster – What is it and why is it important?

Caster is the backward or forward tilt of the steering axis. Vehicle manufacturers are aware of the advantages of caster and as each new model is released the amount of caster specified increases. For example, the VB Commodore was released with around ½ degrees positive castor; the VT now comes standard with around 9 degrees!

Why, because the disadvantages of high levels of castor are being overcome. Rack and pinion steering means less play, lower Ackerman levels, smaller scrub radius (zero is now very common), better and lower profile radial tyres means less sidewall deflection and higher tolerance to greater slip angles. But the greatest obstacle, that of heavy steering effort, has all but disappeared with the universal acceptance of power steering. That’s why Whiteline developed a range of adjustable radius rods  for Commodore, which allow an additional 2.5deg positive caster on VB to VS.

High levels of positive caster equate to dynamic negative camber on turn when you need it most. (Have a look at the front wheels of a Mercedes or Audi when parking.) Whiteline continues to put heavy emphasis on additional positive caster when designing new suspension packages.

Caster - "When too much caster is never enough"? – 5 reasons why.

• Maximise tyre contact patch during roll
• Improve turn-in response
• Increase directional stability
• Maximise tyre contact patch during braking and acceleration
• Improved steering feel and self-centre
• Increases dynamic negative camber (on turn)

Castor Vs camber, try castor first. Why?

• Camber doesn’t improve turn-in, positive caster does.
• Camber is not good for tyre wear.
• Camber doesn’t improve directional stability.
• Camber adversely effects braking and acceleration.

Dynamic & static – what are you talking about?

Typically used when discussing wheel alignment and geometry. By this, Whiteline are referring to the difference in alignment angles between a stationary and a moving vehicle. That is, the same vehicle will typically have different caster, camber and toe readings when it is moving compared to when the alignment was done in static form in the workshop.

In an ideal world, all wheel alignments would be done on a dynamic wheel aligner but these are expensive and quite rare. This concept is very important, as the only suspension angles that really matter are those present while the vehicle is moving (dynamic). What is done to the vehicle’s alignment while the vehicle is stationary, (static) is a process of trying to predict the levels of change while the vehicle is moving and setting the angles according to these predictions.

Whiteline puts a great deal of emphasis on the dynamic geometry so rigorous road testing is essential to ensure that the predictions are valid.

Toe-in or toe-out. Who’s toes and what’s it mean?

Toe is the difference in distance between the front and rear of the tyres. Historically front toe was the only thing that could be modified as rear wheel drive vehicles using a rigid axle had fixed rear toe, usually neutral. Many modern front wheel drives have rear toe adjustment as standard which is critical to their handling.

Current VT Commodores have an independent rear suspension design that has substantial dynamic toe change requiring after market solutions to correct. Whiteline IRS Camber/Toe adjusting kit is designed to around this problem. Essential when lowering. (See IRS for more details)

• Excessive amounts of either will adversely effect tyre wear.
• Excessive toe-in makes the car unresponsive and doughy.
• Excessive toe-out makes the car nervous and lacking in directional stability.
• Minor values are useful for improving turn-in, steering response and masking torque steer.

Setting the correct amount of toe, a case study.

The following is a copy of an e-mail we have answered regarding toe settings on a WRX. It's a useful resource as many modern cars are designed with similar geometry to the WRX making this relevant for many FWD and AWD vehicles.

Questions:
Some argue 1-2mm toe in gives the best response etc. others argue toe out for the rear is the way to go. This almost leads me to believe that 0 toe would be best...

WL responds:
Allowing for language translation, response is not the correct word here. Toe-in can not deliver improved response or turn-in either front or rear.

Question:
Given the fact that the Scoob is a 4wd rear toe setting can be important too, though I know one setting is always a compromise for various conditions. Answering the following questions could help me in my decision:

WL responds:
The more relevant question is one of stability vs instability, front vs rear. Discussed more later.

Question:
What's the reaction of the Scoob when accelerating? Lifting the wheels leading to toe in?

WL responds:
Both front and rear will tend to toe-in marginally under acceleration (torque application), the front more so than the rear. Although fitting the anti-lift kit will also reduce this. The body lift component of accelerative forces will have minimal effect on toe change, albeit towards toe-in.

Friction (resulting from grip under way) will however force some toe-out which is cancelled by drive torque with the net result being close to neutral. (In a front wheel drive or front wheel drive based all wheel drive like the WRX)

Question:
How doe toe react when acceleration out of a corner?

WL responds:
There are 2 separate forces involved here. With respect to acceleration, refer above. As for the consequences resulting from roll, rear change is almost immeasurable. Front change (bump steer by another name) is also negligible. In fact you've got us here as we have never measured it precisely as it is not an issue with the WRX. A precise value would therefore be academic though easily obtainable with a contemporary wheel aligner. Please let me know your vehicles "bump-steer" value if you get this done. Meanwhile, we will also check this at our end.

Question:
What does toe do for turning in?

WL responds:
Historically, static toe-in was used to pre-empt dynamic toe out or to deliver a certain "numbness" to the steering, hence the opposite to response. It does also deliver stability at cruise. Toe neutral is a natural state, where as toe-out is an unstable state. This can be harnessed to deliver exaggerated steering or directional change response to either front or rear. Whiteline recommend marginal toe-out on rear to allow the rear to respond quickly to directional change at the front.

Question
What reaction gives the toe setting when under braking?

WL responds:
The opposite to acceleration.

Question:
Isn't zero toe best for straight-line stability?

WL responds:
Negative scrub radius geometry (only really relevant to front unless Cray super-computer modeling is your pass time) of WRX leads to toe-out off acceleration or when cruising with low torque. Which type of straight-line stability are we talking about here?

Removing torque from the equation, there is now doubt that toe-in delivers more straight-line stability during steady cruise however at the expense of turn-in response. That is why race teams will change the toe values depending on track and race distance. A tight track will see higher values of toe (both in or out depending on driver preference), while endurance races on relatively fast open tracks will see smaller values.

You can conclude from this that you can either promote stability/instability at the front or the rear, using toe to deliver a desired result. We can also conclude that in contemporary steering and chassis design, bump steer effect is negligible and only serves to confuse the argument.