Many people assume fitting aftermarket gear is the only way to improve their car's handling. The truth is, a carefully planned wheel alignment can make a dramatic improvement. What's more, this improvement applies equally to cars with standard or aftermarket suspension systems, and the changes shouldn't cost much to implement.
So what are the wheel alignment adjustments and how can they benefit your vehicle? We spoke with Jim Gurieff of Whiteline to find out... But first, let's find out what all those weird and wonderful terms actually mean.
Toe is the difference in distance between the leading and trailing edge of the wheels at the one end of the car. A car is said to have toe-in when the leading edge of the wheels are closer together than the trailing edge (ie the wheels are pointing slightly inwards to the car's longitudinal centreline), zero toe is where the wheels are parallel with one another, and toe-out is where the leading edge of the wheels are further apart than the trailing edge (ie the wheels are pointing slightly outwards from the car's centreline). Separate toe readings are taken across the front and rear axle lines and the measurement is almost universally expressed in millimetres.
Toe-out reduces lateral stability and increases tyre wear on the outside shoulder. Front-end toe-out will improve turn-in response while rear-end toe-out encourages an oversteer motion. Conversely, rear toe-in helps reduce oversteer, in addition to improving lateral stability and causing inner shoulder tyre wear. Toe-in on the front-end also dampens turn-in response.
Notice that toe adjustment is effectively impossible on beam axles, and an aftermarket kit may be required to allow adjustment on the back of certain IRS cars.
Camber refers to the angle of a wheel away from vertical when viewed from front or rear. Negative camber is where the top of the wheel is closer to the longitudinal centreline of the car than the bottom. A good example of negative camber can be seen on the back of a lowered Datsun 1600, where the top of the wheels very often lean inwards. Zero camber is where the wheel is standing vertically, and positive camber is where the top of the wheel is further away from the car's longitudinal centreline than the bottom.
Negative camber reduces longitudinal (accelerative and braking) grip and aggravates any existing tramlining. (Tramlining is where the wheels follow every longitudinal bump and groove in the road). In addition, if a car isn't driven hard enough, tyres with plenty of negative camber will suffer dramatic wear on the inner tyre shoulders. Negative camber is - however - often used as a pre-emptive approach to improving handling. This is because as a car goes through a corner, its alignment angles change due to chassis, suspension component and bush deflection. These changes see the outside wheel move away from its usual upright position towards positive camber. However, by dialing in some negative camber when the car is stationary, the camber position of the outside (ie loaded) wheel under full cornering loads is much closer to upright. This delivers the maximum available cornering grip.
Camber is generally not factory adjustable. As a guide, it is only cars constructed to broad tolerance that come with camber adjustment.
Castor applies only to a vehicle's steered wheels. It is the angle between the steering axis and the front wheel's vertical centreline when looking at the side of the vehicle. Moving the bottom suspension mount forward, or moving the top suspension mount back, serves to increase positive castor. Notice that this can only be done with an aftermarket castor kit.
The presence of positive castor increases the amount of negative camber that occurs during cornering, which means that once the bush deflection, body roll and other nasties are taken into consideration, the outside tyre ends up being closer to vertical than it otherwise would have been. This means better cornering grip. However - unlike simply dialing in negative camber - positive castor brings no problems in relation to longitudinal grip, tramlining or tyre wear. The only ill-effect is slightly increased steering effort - and this shouldn't be a problem on cars with power steering.
Static vs Dynamic
When the front suspension of the car is set to provide - for example - one degree negative camber on an alignment machine, that is often not what you'll get while cornering. Chassis flex, suspension component movement, bush squish and the changes in geometry caused by body roll all result in dynamic (ie actual on-road) alignment specifications often being quite different to that which is achieved on the wheel alignment machine. It is quite common to experience mid-corner toe variations of a couple of millimetres in conjunction with a ½ degree change in camber!
In fact, you can see some of these changes for yourself if you watch your car being wheel aligned. Once the alignment is finished, get into the driver's seat and ask the technician to re-check the alignment specs. In some cheaper cars the measured parameters will have suddenly altered! And actively changing chassis dynamics is not what you want...
These dynamic geometry changes problems can be partially offset using a strut brace, structural roll cage, seam-welded chassis and hi-grade racing suspension components (such as heavy-duty strut bodies). Firmer bushes also make a noticeable and cost-effective upgrade on most road cars. As an example, this Whiteline castor kit features a polyurethane low-compliance bush, which maintains a more constant on-road alignment. And the more sophisticated the suspension of the car (eg multilink rear ends), the less variation will be found between static and dynamic geometries.
Configurations to Suit Various Cars
Front Wheel Drives
The most common handling complaint in a front wheel drive car is understeer (ie where the front of the car slides first). Adding negative camber and/or an aftermarket castor kit to the front will reduce this problem - both serve to increase front-end cornering grip. Rear toe can also be adjusted to further improve chassis balance, with toe-out making the back axle more unsettled - partly offsetting the car's dominant understeer characteristic.
The owners of some front wheel drive cars - such as the Hyundai FX Coupe - find that their cars oversteer too readily. If this is the case, increase toe-in and negative camber on the rear. This will improve the rear-end's cornering grip and reduce its tendency to slide out from a corner.
Rear Wheel Drives
A solution for understeer in a rear wheel drive car is to increase negative camber and positive castor at the front-end. Both will give the front-end more grip. Toe-out at the rear will also encourage the rear-end to become more active, thus countering some of the understeer.
Oversteer is the traditional handling trait of a rear wheel drive. To alleviate this, you'll need to improve rear-end cornering stability with increased negative camber. Rear toe-in will also make that end more stable. Notice if it's power oversteer you want to get rid of, you'll need to change to a diff centre with less lock-up. This will allow the inside back wheel to lay rubber when you're cornering hard, rather than both wheels losing grip.
With all wheels driving forward, it's natural that these cars don't like to change direction (ie they have poor turn-in). Nonetheless, increasing negative camber on the front-end improves turn-in and cornering grip. Increasing castor will further reduce understeer. It's also possible to attain closer-to-neutral handling by dialling in rear-end toe-out. Again, this encourages an oversteer motion to offset the dominant understeer.
An oversteery full-time 4WD vehicle is very rare. The only Australian-delivered car fitting this description is the four-wheel-steered Mitsubishi Galant VR4. Note, however, the VR4's oversteer transition is caused by its electronically controlled rear-steer system rather than its suspension geometry. Nonetheless, the severity of its rear-end slide can be slightly reduced by increasing toe-in and negative camber on the back.
Any car with 4WS adds another complication to a wheel alignment. All of the adjustments listed above apply to these cars - but it helps to find out if it's the rear-steer system that's causing the handling deficiencies. A simple way to determine this is to disconnect power to the steering control module and go for a careful drive.
How Much Adjustment?
Modern cars usually have generous scope for front toe adjustment. The potential amount of adjustment varies, but - to give you an idea - it's possible to see extremities of up to 20mm toe-in and 20mm toe-out. For most high-performance streetcars, however, you should be looking at somewhere between 3mm toe-in or 3mm toe-out front and rear.
To adjust camber, an aftermarket camber kit is often a necessity as factory adjustment is usually limited. However - before purchasing a kit - it's a good idea to test your car's handling with negative camber set to within factory limitations. This will ensure near-standard levels of tyre wear, longitudinal grip and tramlining. Beyond factory adjustment, anywhere up to 3 degrees negative camber front and rear is considered reasonable on most streeters.
Castor - as mentioned - is not adjustable on most production cars so an aftermarket kit is essential if you wish to make any adjustment in this area. As a guide, you should aim for a 1-2½ degree increase in positive castor with most aftermarket kits. This will create only slightly heavier steering effort.
Thanks to Whiteline for their assistance in compiling this story. Contact: +61 2 9603 0111.
Alignment diagrams courtesy of Bosch.