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Pointed the Right Way
story by john hagerman
Camber, Caster and Toe: What Do They Mean?
The three major alignment parameters on a car are toe, camber, and caster. Most enthusiasts have a good understanding of what these settings are and what they involve, but many may not know why a particular setting is called for, or how it affects performance. Let’s take a quick look at this basic aspect of suspension tuning.
When a pair of wheels is set so that their leading edges are pointed slightly towards each other, the wheel pair is said to have toe-in. If the leading edges point away from each other, the pair is said to have toe-out. The amount of toe can be expressed in degrees as the angle to which the wheels are out of parallel, or more commonly, as the difference between the track widths as measured at the leading and trailing edges of the tires or wheels. Toe settings affect three major areas of performance: tire wear, straight-line stability and corner entry handling characteristics.
For minimum tire wear and power loss, the wheels on a given axle of a car should point directly ahead when the car is running in a straight line. Excessive toe-in or toe-out causes the tires to scrub, since they are always turned relative to the direction of travel. Too much toe-in causes accelerated wear at the outboard edges of the tires, while too much toe-out causes wear at the inboard edges.
So if minimum tire wear and power loss are achieved with zero toe, why have any toe angles at all? The answer is that toe settings have a major impact on directional stability. The illustrations at right show the mechanisms involved. With the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect each other. Under this condition, the wheels are at odds with each other, and no turn results.
When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If it’s a minor disturbance, the disturbed wheel will steer only a small amount, perhaps so that it’s rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still don’t describe a turn. The wheels have absorbed the irregularity without significantly changing the direction of the vehicle. In this way, toe-in enhances straight-line stability.
If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it’s clear that toe-out encourages the initiation of a turn, while toe-in discourages it.
With toe-in (left) a deflection of the suspension does not cause the wheels to initiate a turn as with toe-out (right).
The toe setting on a particular car becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted by toe-out. Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. So street cars are generally set up with toe-in, while race cars are often set up with toe-out.
With four-wheel independent suspension, the toe must also be set at the rear of the car. Toe settings at the rear have essentially the same effect on wear, directional stability and turn-in as they do on the front. However, it is rare to set up a rear-drive race car toed out in the rear, since doing so causes excessive oversteer, particularly when power is applied. Front-wheel-drive race cars, on the other hand, are often set up with a bit of toe-out, as this induces a bit of oversteer to counteract the greater tendency of front-wheel-drive cars to understeer.
Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This is another reason why many front-drivers are set up with toe-out in the front. Likewise, when pushed down the road, a non-driven wheel will tend to toe itself out. This is most noticeable in rear-drive cars.
The amount of toe-in or toe-out dialed into a given car is dependent on the compliance of the suspension and the desired handling characteristics. To improve ride quality, street cars are equipped with relatively soft rubber bushings at their suspension links, and thus the links move a fair amount when they are loaded. Race cars, in contrast, are fitted with steel spherical bearings or very hard urethane, metal or plastic bushings to provide optimum rigidity and control of suspension links. Thus, a street car requires a greater static toe-in than does a race car, so as to avoid the condition wherein bushing compliance allows the wheels to assume a toe-out condition.
It should be noted that in recent years, designers have been using bushing compliance in street cars to their advantage. To maximize transient response, it is desirable to use a little toe-in at the rear to hasten the generation of slip angles and thus cornering forces in the rear tires. By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system.
THE EFFECTS OF CASTER
Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it’s tilted forward, then the caster is negative.
Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The mechanism that causes this tendency is clearly illustrated by the castering front wheels of a shopping cart (above). The steering axis of a shopping cart wheel is set forward of where the wheel contacts the ground. As the cart is pushed forward, the steering axis pulls the wheel along, and since the wheel drags along the ground, it falls directly in line behind the steering axis. The force that causes the wheel to follow the steering axis is proportional to the distance between the steering axis and the wheel-to-ground contact patch-the greater the distance, the greater the force. This distance is referred to as «trail.»
Due to many design considerations, it is desirable to have the steering axis of a car’s wheel right at the wheel hub. If the steering axis were to be set vertical with this layout, the axis would be coincident with the tire contact patch. The trail would be zero, and no castering would be generated. The wheel would be essentially free to spin about the patch (actually, the tire itself generates a bit of a castering effect due to a phenomenon known as «pneumatic trail,» but this effect is much smaller than that created by mechanical castering, so we’ll ignore it here). Fortunately, it is possible to create castering by tilting the steering axis in the positive direction. With such an arrangement, the steering axis intersects the ground at a point in front of the tire contact patch, and thus the same effect as seen in the shopping cart casters is achieved.
The tilted steering axis has another important effect on suspension geometry. Since the wheel rotates about a tilted axis, the wheel gains camber as it is turned. This effect is best visualized by imagining the unrealistically extreme case where the steering axis would be horizontal-as the steering wheel is turned, the road wheel would simply change camber rather than direction. This effect causes the outside wheel in a turn to gain negative camber, while the inside wheel gains positive camber. These camber changes are generally favorable for cornering, although it is possible to overdo it.
Most cars are not particularly sensitive to caster settings. Nevertheless, it is important to ensure that the caster is the same on both sides of the car to avoid the tendency to pull to one side. While greater caster angles serve to improve straight-line stability, they also cause an increase in steering effort. Three to five degrees of positive caster is the typical range of settings, with lower angles being used on heavier vehicles to keep the steering effort reasonable.
Like a shopping cart wheel (left) the trail created by the castering of the steering axis pulls the wheels in line.
Camber is the angle of the wheel relative to vertical, as viewed from the front or the rear of the car. If the wheel leans in towards the chassis, it has negative camber; if it leans away from the car, it has positive camber (see next page). The cornering force that a tire can develop is highly dependent on its angle relative to the road surface, and so wheel camber has a major effect on the road holding of a car. It’s interesting to note that a tire develops its maximum cornering force at a small negative camber angle, typically around neg. 1/2 degree. This fact is due to the contribution of camber thrust, which is an additional lateral force generated by elastic deformation as the tread rubber pulls through the tire/road interface (the contact patch).
To optimize a tire’s performance in a corner, it’s the job of the suspension designer to assume that the tire is always operating at a slightly negative camber angle. This can be a very difficult task, since, as the chassis rolls in a corner, the suspension must deflect vertically some distance. Since the wheel is connected to the chassis by several links which must rotate to allow for the wheel deflection, the wheel can be subject to large camber changes as the suspension moves up and down. For this reason, the more the wheel must deflect from its static position, the more difficult it is to maintain an ideal camber angle. Thus, the relatively large wheel travel and soft roll stiffness needed to provide a smooth ride in passenger cars presents a difficult design challenge, while the small wheel travel and high roll stiffness inherent in racing cars reduces the engineer’s headaches.
It’s important to draw the distinction between camber relative to the road, and camber relative to the chassis. To maintain the ideal camber relative to the road, the suspension must be designed so that wheel camber relative to the chassis becomes increasingly negative as the suspension deflects upward. The illustration on the bottom of page 46 shows why this is so. If the suspension were designed so as to maintain no camber change relative to the chassis, then body roll would induce positive camber of the wheel relative to the road. Thus, to negate the effect of body roll, the suspension must be designed so that it pulls in the top of the wheel (i.e., gains negative camber) as it is deflected upwards.
While maintaining the ideal camber angle throughout the suspension travel assures that the tire is operating at peak efficiency, designers often configure the front suspensions of passenger cars so that the wheels gain positive camber as they are deflected upward. The purpose of such a design is to reduce the cornering power of the front end relative to the rear end, so that the car will understeer in steadily greater amounts up to the limit of adhesion. Understeer is inherently a much safer and more stable condition than oversteer, and thus is preferable for cars intended for the public.
Since most independent suspensions are designed so that the camber varies as the wheel moves up and down relative to the chassis, the camber angle that we set when we align the car is not typically what is seen when the car is in a corner. Nevertheless, it’s really the only reference we have to make camber adjustments. For competition, it’s necessary to set the camber under the static condition, test the car, then alter the static setting in the direction that is indicated by the test results.
The best way to determine the proper camber for competition is to measure the temperature profile across the tire tread immediately after completing some hot laps. In general, it’s desirable to have the inboard edge of the tire slightly hotter than the outboard edge. However, it’s far more important to ensure that the tire is up to its proper operating temperature than it is to have an «ideal» temperature profile. Thus, it may be advantageous to run extra negative camber to work the tires up to temperature.
(TOP RIGHT) Positive camber: The bottoms of the wheels are closer together than the tops. (TOP LEFT) Negative camber: The tops of the wheels are closer together than the bottoms. (CENTER) When a suspension does not gain camber during deflection, this causes a severe positive camber condition when the car leans during cornering. This can cause funky handling. (BOTTOM) Fight the funk: A suspension that gains camber during deflection will compensate for body roll. Tuning dynamic camber angles is one of the black arts of suspension tuning.
TESTING IS IMPORTANT
Car manufacturers will always have recommended toe, caster, and camber settings. They arrived at these numbers through exhaustive testing. Yet the goals of the manufacturer were probably different from yours, the competitor. And what works best at one race track may be off the mark at another. So the «proper» alignment settings are best determined by you-it all boils down to testing and experimentation.
Learn Camber, Caster, and Toe
A good alignment will make your car handle, brake, and accelerate better for very little investment. You’ll even save money by reducing tire wear with a simple correction to the camber and toe.
What is Camber Angle?
Camber is a measurement of the centerline of your wheel/tire relative to the road surface. It is expressed in degrees and greatly affects the handling dynamics of the car.
Negative Camber
Benefits of Negative Camber
Negative camber improves handling by keeping the tire perpendicular to the road as the car rolls; ensuring that the tire’s contact patch is evenly loaded. Without adequate negative camber the tire would load the outer portion of the tire and produce less grip.
Downsides of Negative Camber
Static vs. Dynamic Camber
Static camber is the amount of camber angle the vehicle has at a rest, and is what gets measured when you get an alignment.
Dynamic camber is the momentary amount of camber angle generated as the vehicle accelerates, brakes, and goes around corners. Dynamic camber is the static camber plus or minus the «camber gain.» Camber gain is rarely linear and is a result of suspension design and geometry. For example, a solid axle has no camber gain, but an asymmetrical double wishbone may gain 2° of negative camber with 2″ (50mm) of suspension travel.
Camber Gain
Different suspension designs will result in varied camber gain curves, and even two similar designs can result in widely varied camber gain. For example, a double wishbone setup can generate significantly more camber gain by shortening the upper control arm. Here’s a couple more examples:
How Much Static Camber Should I Run?
The ideal amount of camber for handling performance comes from a couple of variables:
Put simply, the amount of suspension travel and how much camber is gained as the suspension travels will dictate how much static camber you need to run.
As a rough guide, here’s a list of camber settings for various suspension layouts and vehicles. This is meant to be a good starting point for a street car setup, but will require adjustment to fit your needs and vehicle specifics.
These settings are meant to be a good starting place for a street car with street radials. Your vehicle may prefer more or less camber.
Front Camber Setting
| Drive Layout | Suspension Type | Camber Angle |
|---|---|---|
| FWD | MacPherson Strut Double Wishbone | 2.0° 1.5° |
| RWD | MacPherson Strut Double Wishbone | 2.5° 2.0° |
| AWD | MacPherson Strut Double Wishbone | 2.5° 2.0° |
| 4WD | MacPherson Strut Double Wishbone | 1.0° 1.0° |
Rear Camber Setting
| Drive Layout | Suspension Type | Camber Angle |
|---|---|---|
| FWD | Multilink Trailing Arm Twist Beam | 1.0° 1.0° 1.0° |
| RWD | Multilink Trailing Arm Swing Arm | 1.0° 1.0° 1.3° |
| AWD | Multilink Double Wishbone Trailing Arm | 1.0° 1.0° 1.0° |
| 4WD | Multilink Double Wishbone Trailing Arm | 0.5° 0.5° 0.5° |
Race teams will know how much camber to dial into their car from thermal tire data (tire tread temps), tire wear patterns, previous track experience, and driver feedback. Well-funded teams will have additional data from load cells, shock travel, acceleration sensors, images, and onboard telemetry using thermal cameras.
At proper camber settings the tire will exhibit stable and symmetrical temperatures across the tire surface during cornering. Excessive heating on the inner or outer third of the tire can be indicative of improper camber angle, although not conclusively.
Road conditions can also demand more or less camber. Loose gravel and wet pavement both limit the amount of overall tire grip available, which necessitates less static camber. Banked corners at NASCAR oval tracks require asymmetrical camber setups with positive camber on the LF tire and considerable negative camber on the RF (outer) tire.
Camber Settings for Drift Cars
The rear should have near zero camber to provide strong forward grip and more importantly, to last quite a bit longer. By using the entire tread face you will evenly distribute pressure along the tire and heat it more uniformly. Both of these things will contribute to a lot more fun-per-tire (reduced tire wear), but at the cost of needing more power than running say 5° of camber and nuking the inner edge.
Positive Camber
Positive camber is when the top of the tire extends outward, and the base of the tire tucks inwards. This is rarely ever seen on a road car since it will reduce road handling capability. In special situations, such as NASCAR, positive camber will be applied to handle heavy amounts of track embankment. If you are running a positive camber figure on your street car then its highly recommended that you inspect your suspension for damage and/or adjust the camber to a slight negative figure.
Vintage Vehicles
Older vehicles can have very unique needs depending on their suspension design. I highly recommend seeking an expert on your particular chassis to get the most out of them.
Camber Settings with Bias Ply Tires
Bias ply tires react very differently to camber angle due to the differences in their construction compared to radials. Using the above recommendations, which are meant for radials, can result in lackluster results. Typically, you will run a bias ply tire with considerably less camber. Again, I recommend consulting an expert for further assistance on your vintage setup.
What is Caster Angle?
Caster is the measure of how far forward or behind the steering axis is to the verticle axis, viewed from the side. An example of caster in action is the front wheels on a shopping cart. They run a large amount of positive caster to make the cart track straight without wandering. However, the method that the cart uses (displacement caster) is different than how your car develops its caster angle (angled pivot), but the effect is the same.
Positive Caster
Positive caster is when the steering axis is in front of the verticle. In a road car, this would mean that the top of the coilover would be pushed towards the rear of the car. Positive caster creates a lot of align torque (the force that straightens the steering wheel when you go forward) which improves straight line stability of the car. Due to the geometry of positive caster it also will increase negative camber gain (a good thing) when turning. As you increase positive caster the steering will get heavier also, but with modern power steering systems this is rarely a problem. Generally you want as much positive caster as you can reasonably get so long as the car is equipped with power steering.
Negative Caster
Negative caster is when the steering axis is behind the vertical. This is generally only found on older vehicles due to tire technology, chassis dynamics, and other reasons. Modern vehicles do not use negative caster. It will lighten the steering effort but also increases the tendency for the car to wander down the road. If you’ve ever pushed a shopping cart then you’ve felt the effects of negative caster on the front wheels.
Regardless of what caster setting you use, make sure that your caster is symmetrical. Running a different amount of caster on one side will cause the car to pull towards the side with less caster.
What is Toe Angle?
Toe is the measure of how far inward or outward the leading edge of the tire is facing, when viewed from the top. Toe is measured in degrees and is generally a fraction of a whole degree. It has a large effect on how the car reacts to steering inputs as well as on tire wear. Aggressive toe angle will cause the tire to develop feathering across its surface.
Toe In
Toe-in is when the leading part of the tire is turned inwards towards the center of the car. This makes the tires want to push inward, which acts to improve straight line stability of the car as its traveling down the road, particularly at high speed (highway).
Toe Out
Toe-out is when the leading part of the tire is turned outwards away from the center of the car. This makes the tires want to separate from each other. This improves turn-in response considerably, but at the cost of tire wear. Running toe-out in the rear is generally not recommended since it will make the car want to pivot (oversteer) at all steering angles, but in the right setup it can help (auto-x / technical tracks) particularly if the rear toe bumps in.
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Understanding Camber, Caster, and Toe
Whether you’re getting behind the wheel of a family sedan or a 4×4 with plenty of ground clearance, proper alignment goes a long way. You want to be able to go around a corner without spilling your latte or energy drink, and you certainly want to be able to drive in a straight line without fighting your way through every mile. When the camber, caster, and toe are properly aligned to your vehicle’s specifications, it’s easy to forget about those settings. But when any of the three are out of alignment, you’ll notice it in your steering wheel, gas mileage, and tire wear.
Here’s how camber, caster, and toe help you get the most from your tires and fuel economy, and improve your safety and handling.
Camber Affects Tire Wear
The inward and outward tilt of the tire and wheel assembly (viewed from the front of the vehicle) is called camber. When the top of the tire is leaning inward, it is a negative camber. Positive camber has the top of the tire tilting outward. Each manufacturer sets a specific camber alignment for every vehicle it produces, which might be either positive, negative or zero (0º). When the camber is at the correct angle, the tire and wheel will roll straight.
Generally, camber plays a key-role in cornering performance. If the camber is out of the manufacturer’s range, it can cause handling issues and excessive tire wear, which costs you money. If a vehicle has rear-camber adjustments, adjusting the rear camber plays a big role in straight-line stability and cornering.
Caster Affects Steering and Handling
Ever tried to ride a bicycle without using your hands? The fact you could meant that your bicycle had a positive caster. If the caster had been zero (0º) or negative, riding that way would be nearly impossible. The same can be said for your vehicle.
Modern vehicles run a certain amount of positive caster with the steering axis tilted rearward toward the driver. While caster doesn’t affect tire wear like camber, it does have a big impact on steering and handling.
The higher the caster, the more stability a vehicle will have at higher speeds. Lower caster equals more responsive handling.
Toe is the Most Important Angle for Tire Life
Of all the angles, the toe can fall out of alignment the easiest. A toe that is properly calibrated to manufacturer specifications (which can be either slightly positive or negative) will be at zero (0º) when on the road. This means all of the tire and wheel assemblies (front and rear) are pointing in the same direction.
What does it mean when the toe is out of alignment? It means your tires are wearing out faster than they should and you’re burning more fuel than is necessary. When the toe is at the correct angle, there’s less friction on the tires as they roll. When they are facing away from each other (toe-out) or toward each other (toe-in), they’re essentially scrubbing on the road ever so slightly with every passing mile.
Les Schwab Does Alignments
At Les Schwab, we want to help you get the most out of your tires. If you haven’t had your alignment checked in a while, or you suspect an issue, stop by any of our stores. Our experts will show you what is needed to get your camber, caster, and toe back within your manufacturer’s specifications for prolonged tire life, improved safety and handling, and increased fuel economy.
