April 14th, 2017 by Matt Holden
If you own a car, you’ve experienced the pain of having a wheel go out-of-alignment and probably noticed the car didn’t quite behave in the same way it used to. On a street car this pull is an annoyance, but in racing it’s an advantage! In all forms of motorsport from karting to Formula 1 to World Rally, wheel alignment is a well-studied art form, and proper settings can make a decent car great just as easily as it can make a dominant car transform into a dud. Of the three major alignment options available to us, we’re going to look at Camber this week and all of the mechanics behind it that wind up making a race car faster because of it.
What is Camber?
Camber is the vertical angle of the tire relative to the reference plane it is sitting on, be it a setup plate or the racing surface. If the tire is perfectly vertical (and perpendicular to the reference plane), we have zero camber. If the top of the tire is farther from the car than the bottom of the tire, we have “positive” camber, and if the top of the tire is closer to the car than the bottom, we have “negative” camber. While it’s hard to visualize camber on a car with fenders covering up the wheels, it’s very easy to see it on an open-wheel car. Here’s the NASCAR Modified with both extremes of front camber shown:
The laws of physics say that the more surface area we can get between the tire and the road, the more traction is available in that tire. Ideally, having exactly zero camber on a perfectly flat surface will yield the largest tire contact patch available and thus the highest amount of traction a given tire can produce. The more traction we have on a tire, the more lateral force it can produce. The more lateral force, the faster we can go around a corner! So it would make sense to just set the camber at vertical and leave it there, right? No, because there’s more voo-doo at work here….
One of the biggest reasons why camber is never set at a perfect 0° vertical angle is due to camber gain, or the change in the wheel’s camber angle through suspension travel. This effect is due to the change in horizontal length of the suspension control arms as the wheel moves up or down and is present in every type of suspension with rotating control arms. On suspensions without these arms, such as the solid rear axle suspension found in most stock cars, or the solid axles at both ends of a sprint car, camber gain does not exist and camber angles remain constant through suspension travel.
This diagram illustrates camber gain through downward travel of a double-arm independent suspension system. This is common on most race cars at all four wheels, but only the front suspension of a stock car. As the chassis drops, whether due to braking, downforce, or track loading, the suspension arms trace an arc as they rotate around the fixed points at each end of the arm. These arcs cause the horizontal length of the arm to change through suspension travel, and as a result the arms will “pull” the ball joints on the wheel spindle assembly inward at the top of the tire. This results in the wheel “gaining” camber angle through travel. Conversely, as the chassis rises for whatever reason, the opposite will occur and the wheel will lose camber, becoming more vertical relative to the ground.
Similarly, as a car rolls outward through a turn, camber will change as well. If we enter a right-hand turn, the car will roll to the left. This causes the upper control arm to be pushed outward at the chassis, which pushes the upper ball joint on the wheel outward as well. This reduces the camber angle and straightens the wheel to where it’s more vertical than it was on corner entry. But wait, there’s more….
The last major component to camber angle is known as “camber thrust”. As a tire is leaned in one direction or the other, a force will be generated at the contact patch in the direction of lean. The higher the camber angle, the more this camber thrust force will be. It’s part of the reason why your bicycle will turn in one direction or the other by simply leaning it to one side without turning the handlebars. Motorcycle racing can take this to an extreme, and their low-sidewall, rounded tires help to produce such extreme lean angles in corners.
It’s important to understand that this force always increases with increased camber values. This is especially apparent in oval racing, where front camber values can be very high on the left-front tire, since it experiences a lighter load than the right-front, as well as right-front camber values increasing for high-grip tracks and qualifying where tire life isn’t a concern.
Put it all together
As you can see, camber isn’t as simple as simply leaning the tire in one direction and assuming it’s going to work. We’re balancing three unique aspects to get the most grip we possibly can from a tire, and finding the optimum point for all three settings will result in the best performance from our tires.
Obviously, our first consideration is going to be the contact patch size. For a racing tire, the contact patch size could be something around the size of your shoe (or even smaller) and there’s a lot of load that will go into such a small area. The more rubber we can put on the track, the better it’s going to stick. However, as we add more camber beyond the angle to produce the largest contact patch, we start to add in the camber thrust force which will combine with the lateral forces produced at the tire’s contact patch. The two forces are going to add together with the thrust force increasing with camber angle and lateral traction force decreasing with camber angle. There will be a point, however, where the increase in thrust force is outweighed by the decrease in lateral traction force. Beyond this point, lateral forces at the tire will begin to decrease and we lose cornering grip. In every situation, this angle to produce peak force is not the camber angle that will produce the largest contact patch. In addition, the camber angle that produces the largest contact patch will not produce the highest cornering force. This is why race cars will always have some negative camber value in the turns at maximum travel.
Setting Camber – Road Racing
For road racing, this is relatively simple: We’re going to camber all four tires in the negative direction, and look to have a large contact patch on the outside tires while the inside tires can be largely ignored for a given turn direction. Ideally, the car needs a large amount of traction on the outside tires in order to keep it going around the corner, so the camber should be set to do just that. Depending on the car, it may be desirable to have extra camber beyond that for the thrust aspect. A heavy car with low downforce may need more camber than a lighter car with high downforce. V8 Supercars typically have very high camber angles in the corners while a Formula-type car will have relatively low camber angles.
Setting Camber – Oval Racing
As with everything else, the asymmetry of oval racing makes things infinitely more complex. In a left-turn oval, all four tires will lean to the left if rules allow it. Left-side tires will have positive camber, right-side tires will have negative camber. This produces something that could be called “mechanical sideforce” since the camber thrust from all four tires will be pushing the car towards the left in the same way that aerodynamic sideforce produced a net force towards in the inside of the corner.
The uniqueness of oval racing’s high (and varying) loads on all four tires can often produce four unique camber angles at each tire. Since the right-front tire will see a heavy load in both vertical and lateral directions, it’s not uncommon to see lower camber angles at faster tracks to produce a large contact patch and a higher traction capacity while sacrificing the camber thrust aspect of the camber angle. On the other side of the car, the left-front sees a much lower load and it’s not unheard of to run maximum allowed camber angles on that tire. After all, we are losing camber from vertical travel, and the lower loads don’t need such a large contact patch to stay attached to the track!
Rear camber is unique on stock cars due to the lack of camber gain through suspension travel. Since the rear wheels are solidly connected to the axle housing, they will maintain whatever camber angle is set in the garage at all times, making it easier to deal with. Still, every sanctioning body has rules on rear camber values with most mandating no rear camber at all. NASCAR, however, allows rear camber in the top-three series, and not taking advantage of that is leaving speed (and that mechanical sideforce mentioned earlier) on the table. While the right-rear tire should remain at the razor’s-edge limit of what’s allowed, the left-rear can be moved around depending on the track’s characteristics. For example, every car that I’ve put on track at Gale Force Racing has had maximum right-rear camber, however left-rear camber tends to be lower as grip level in the track decreases, resulting in a large left-rear contact patch and a freer corner entry.
It’s extremely important to understand that camber is NOT a handling adjustment and should never be treated as such. As we can see, camber angle balances multiple forces on what is essentially a physics-based knife edge. While most adjustments on the car have a “sweet spot” that you can work within, there is an optimum camber angle for each track/car/tire combination and moving around that zone does nothing but reduce performance. If you add right-front camber on an oval car and you pick up speed, then you weren’t at the optimum angle. However if you adjust the angle and performance is lost, you’ve moved outside of the optimum zone and you cannot get that back any other way. Always check the tires on longer runs in practice to see if wear and temperatures are off before making any alignment adjustments. Never, ever, everever, everevereverever think “My car’s tight” and just throw camber at it. That’s a fantastically easy way to ruin your car.
While shocks, springs, and everything else on a car can be updated in future iRacing builds, alignment mechanics are largely going to remain unchanged in the future. We have everything that could possibly be consdered, from camber gain to tire sidewall rollover, so what we currently have is about as realistic as it’s going to get. Outside of rule changes to various series, we shouldn’t see much change in how camber angles are approached and adjusted. It’s a simple thing on the surface with layers of complexity, but the good thing is that we’ve got all the complexity we can possibly get, and that’s awesome.
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