Understanding Caster and Camber for Suspension Setup

Suspension alignment has a major impact on a car’s driving characteristics. Alignment literally affects where the rubber meets the road, and it can become very clear from behind wheel when things are out of spec. Alignment also affects tire wear, and for many of us the first sign that something is amiss is a bald stripe on the inside or outside of the tire.

Caster and camber are two suspension settings that can profoundly affect performance, tire wear, and the driver’s feeling of connection to the car. For our late model daily drivers, it’s usually ok to drop the car off at the alignment shop and trust that they will set it up to the factory spec. But for our race cars, classics, and custom fabricated projects, it’s important to understand what caster and camber are and how adjusting them can impact performance.

Caster is best described as a vertical line that runs through the two pivot points in your car or trucks suspension. Most often, these pivot points are the upper and lower ball joints in your double A-arm style suspension system. If your vehicle has a McPherson strut style front suspension, then your 2 pivot points would be the lower ball joint and the strut tower mount. Caster is changed by rolling that vertical line forward, resulting in negative caster or by rolling that vertical line backward, resulting in positive caster.

Caster angles are built into your suspension. Some suspensions have a small amount of caster adjustment, but sometimes caster changes will require changing out the hard parts that make up your suspension. An exception to this rule can be found in many modern aftermarket performance suspensions like the Speedway Motors G-Comp. These suspensions will make caster adjustable as a tuning tool. G-Comp suspensions come with interchangable "slugs" that fit into the upper control arm and precisely adjust caster. Caster angles are generally used to improve a vehicle’s steering balance and front-end cornering stability. Caster will also help with high-speed stability.

The principle is the same on a straight axle car like a gasser or an early Ford. on these cars, caster is referring to the angle of the kingpin when viewed from the side. Typically, these cars need to have the proper caster built into the chassis. 5-7 degrees of positive caster is generally a good starting point for straight axle cars. Remember that this is relative to the ground, so if the chassis is flat on a frame table but will sit on a rake, the rake angle will need to be added to or subtracted from that figure.

Almost always, the more positive caster you have built into your race car or street car, the better. By making positive caster gains, you will notice it may become more difficult to steer. This is because as positive caster increases, steering effort also increases. You're essentially lifting the wheel and tire as you increase caster. This increased effort usually goes unnoticed in most vehicles with a power steering setup, but may be an issue with manual steering. Gaining positive caster will further increase straight-line tracking and will also increase the tire lean angle when cornering.

Camber is equally important to your setup recipe, whether you are racing in any form or just out enjoying street driving. Camber is how far the tire slants away from a perfect vertical line when looking at your car or truck from the front. It is measured in degrees, just like caster, and is generally easier to adjust to suit various track conditions, layouts, various street driving scenarios, driving styles, etc. Negative camber is when the top of a tire tilts inward, toward the center of the vehicle. Positive camber is when the top of the tire tilts outward, away from the center of the vehicle. Adjustments are typically made by adding or removing spacers between the upper control arm and its mounting point on the framerail.

It's difficult to prescribe a one-size-fits-all camber recommendation. It really does depend on a multitude of factors such as suspension design, driver preference, tire size and type, etc. In terms of racing applications, a driver that tends to enter the corners aggressively, carrying a lot of speed will benefit from more negative camber, as the increase will further help the retain cornering grip, stability, and decrease tire wear. On the flip side, a more timid driver would enter the corner at a slower speed; with this same negative camber, the result would be a harsh increase in tire wear along the inside edges of the front tires. Large increases in negative camber can be bad and finding the sweet spot is the goal that every driver will be faced with. Too much negative camber will cause your car or truck to lose straight-line stability and grip in quick acceleration and quick stop situations.

Camber is much more difficult to adjust on a straight axle car. Typically the only way to make this adjustment is to actually bend the axle. Most aftermarket straight axles will have the proper camber built in. For original axles that are out of spec, shops that are used to working on big trucks are often equipped to make these adjustments.

Many OE performance cars and aftermarket performance suspension independent systems will have camber gain built into the suspension geometry. The idea here is that as the suspension compresses, as it will on the outside of the car in a hard turn, the tire gains negative camber. This keeps more of the tire's contact patch on the ground for increased traction and speed through the corner.

It's important to understand caster and camber and how they affect your car's performance. But it's also important to remember that suspensions are complex systems and often making a change to a static adjustment will have a greater affect dynamically, and sometimes a change to one setting will also affect another. Camber gauges are great tools to aid setup and measure dynamic changes through suspension travel as caster and camber are adjusted. Additionally, monitoring tire wear and making incremental adjustments will help you find the sweet spot for your chassis and driving style.