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Why 4-Wheel Alignments Matter in Calibrations

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Thrust line

Nov. 13, 2020—After a short technical delay, a  Hunter Engineering representative presented an overview of ADAS systems and the importance of vehicle alignments as part of the virtual AAPEX Experience on November 3.

Dave Fox, senior instructor at Hunter, led the video event and explained how four-wheel alignments are crucial to the ADAS calibration process.

“Two-wheel alignments are a thing of the past,” he said.

 

Thrust Line

The four-wheel alignment is needed because it aligns the vehicle to its thrust line rather than its geometric center line.

“When new, all advanced driver assistance systems were calibrated at the factory to the vehicle’s thrust line,” Fox said. “For best results, these systems need to reference the vehicle’s thrust line during recalibration also.”

The geometric center line is the line extending out from the center of the vehicle body. The thrust line is the direction that the rear wheels are pointed. Those rear wheels must be adjusted first as part of a four-wheel alignment to ensure accurate calibration of the steering angle sensor.

“In a four-wheel alignment, the rear wheels are adjusted to achieve a zero or near zero thrust angle before any front wheel adjustments are made,” Fox said.

This is an increasingly common part of ADAS calibrations. Fox said that four in 10 vehicles require a steering angle sensor reset during a wheel alignment. Because of electronic stability control, seen out of 10 vehicles in the 2012 model year or newer require that reset.

Failure to correctly align the wheels could throw off ADAS sensors, which leads to poor driving conditions.

“Faulty sensor input can cause a warning light or message on the instrument panel, a DTC being stored in the vehicle’s memory, steering wheel vibration, vehicle steering pull, increased steering effort,” Fox said.

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