Why Wheel Alignment Has Become Critical to ADAS Performance

Since the early days of the automobile, wheel alignment has been an important part of vehicle service and repair. It has always been fundamental to vehicle handling, tire wear, and passenger comfort. But today, it has become an even more critical service that technicians provide their customers, and that is because of all the advanced driver safety systems that are incorporated into the modern vehicle. While ADAS systems should not be a foreign concept to today's technician, it's just as important for the technician to have a firm understanding of the foundation these systems are built on, as well as the systems themselves.

Modern vehicles are dependent on a network of sensors. Things like cameras, radar, LiDAR, and ultrasonic sensors are constantly interpreting the world around them. The vehicle needs to use the data these sensors provide to make split-second decisions about what is straight, level, centered, and moving. And the vehicle bases this all on one fundamental assumption: that the vehicle's geometry is correct.

A Game of Inches

In the 2000 movie “The Patriot,” Mel Gibson's character reminds his two young sons to "aim small, miss small" as they wait in ambush for a squad of British Red Coats. ADAS functionality relies on accuracy, and that system accuracy is dependent upon the foundation it's built upon being true. A forward-facing radar module may be mounted correctly to its bracket, its bracket may be mounted securely and correctly to the radiator core support, and the vehicle can have a successful static calibration of that system. But if the thrust angle is off and the vehicle isn't tracking straight down the road, the ADAS systems that rely on an input from that module will not work as effectively as designed. If that forward-facing radar module is even one degree off from the direction of travel, at 100 yards, that module will be off target by more than five feet. At 75 mph, that vehicle is traversing over 36 yards per second, so if you can see why accuracy is important.

Understanding the Technology

To understand why alignment geometry is so important for ADAS performance, it's critical to understand how these systems operate. Every ADAS input—camera, radar, or sensor mounted to a vehicle—is going to be calibrated relative to that vehicle's frame of reference. Basically, that vehicle's centerline, thrust angle, and the level horizon.

When a technician performs a calibration on a forward-facing camera, for instance, they don't just teach the system to recognize a pattern; they also help it define where straight ahead is, where the level horizon is, and what the vehicle considers centered in the lane. If the geometric assumptions the vehicle makes are correct, the ADAS module has a baseline that is reliable to interpret lane markings, oncoming traffic, pedestrians, and other obstacles. If they are not, then every decision the vehicle makes is based on that built-in error. Forward-facing cameras, radar modules, blind spot sensors, and 360-degree camera systems all depend to varying degrees upon accurate base alignment geometry and ride height. ADAS calibrations don't just aim sensors; they help synchronize the ADAS system and the vehicle's physical geometry, and geometry starts with alignment.

The Chain of Accuracy

ADAS accuracy does not start with target boards and a scan tool; it starts with the alignment rack. We have established that virtually every step in the calibration process depends on accurate alignment. Yet not all manufacturers call out a complete four-wheel alignment as step one in the calibration process, or they leave it as an optional step for the technician. Just because the repair a technician performed that triggered the need for an ADAS calibration does not call for a wheel alignment, does not mean that for certain calibrations the alignment should not be checked. How else would the technician know that the vehicle entered the bay with an accurate alignment to begin with? This falls back on the technician to have that firm understanding of system design and overall concept of operation.

Remember, the alignment identifies the geometry, and inputs from systems like the steering angle sensor confirm the driver's intent. It's imperative that the alignment geometry is true and that proper steering angle resets have been made before a target has been placed in front of a vehicle. This chain of events has to happen precisely and to the manufacturer's specifications because when any link in the chain is compromised, the result is an ADAS calibration that appears to have completed successfully, but does not reflect the vehicle's true driving direction. There may not be a fault code set, but the vehicle will not interpret the road as it should.

Proper alignment, verified on level, calibrated equipment, is a critical first step in an ADAS calibration procedure. To treat an alignment as a separate or optional task is only inviting unnecessary risk and headache for the driver and technician.

The Hidden Variables

Wheel alignment data doesn't exist in isolation; this data is a product of suspension geometry, which itself is interdependent on vehicle ride height. For vehicles equipped with ADAS systems, ride height isn't just about vehicle appearance or tire wear. It's a direct input to how cameras, radar modules, and other sensors perceive the world. When the vehicle sits higher or lower than designed, every camera and sensor's aim changes.

Forward-facing radar modules and cameras are calibrated precisely, and a change of a few millimeters in ride height will alter the camera or sensors' aim by fractions of a degree, which is enough to alter its detection field significantly farther or shorter than intended. A vehicle that is heavily loaded in the rear, for instance, is going to travel with a nose high angle of attack, effectively tilting the radar up as well. The radar is now aimed too high, affecting its short-range accuracy, and it could affect its ability to detect closer objects. The same geometry affects camera pitch angle, changing the way the camera interprets things like lane markings. Now, obviously, the loading of vehicles cannot be avoided, but if a vehicle is going to consistently be loaded, additional effort could be made to level that vehicle out under load, keeping equipped ADAS systems online and functioning as designed.

Inputs like ride height sensors are also key components in ADAS systems. A quick look in data stream to verify correct operation can alleviate future headaches for a technician. These sensors are feeding information to the ADAS system, and improper operation could cause an attempted compensation for a false pitch or roll condition.

Many OEM calibration procedures explicitly call for verification of ride height before starting the calibration process. But all too often this step is overlooked. Yet persistent calibration failures or inconsistent system performance can lead directly back to vehicle ride height.

Invisible Offenders

We have well established that inputs like the forward-facing camera and radar modules are dependent upon the vehicle's thrust angle and centerline meshing up. We need the vehicle to travel in the direction the camera and radar are pointed at, or they won't be effective in alerting us to dangers in the vehicle's path.

Many technicians don't spend enough time thinking about the vehicle holistically in terms of mechanical repair. It's not unheard of for a technician to need to drop a rear cradle to gain enough room to pull a fuel tank to replace a pump module or replace a rear differential assembly. Any service that can change the rear toe angles should have an alignment included with the quote, again, to make sure that the ADAS system is being built upon a square foundation.