The evolution of wheel alignment: 1978 - Present

 
 

Thrustline alignment for vehicles with non-adjustable rear wheels

By the late 1970s, new steering and suspension designs ushered in advancements in alignment technology. In 1978, Hunter Engineering introduced the first alignment system capable of measuring rear individual toe, providing the information to determine the direction of travel of the rear wheels, which came to be known as thrustline.

Thrustline alignment became the common procedure to service rear-wheel-drive vehicles with non-independent rear suspensions.

Like centerline alignment, the thrustline alignment procedure adjusts only the front individual toe angles, but uses the thrustline as a reference instead of the geometric centerline. Using the thrustline allowed the technician to achieve a straight steering wheel for the first time and extend tire life. But the inability to adjust the rear wheels continued to produce dogtracking issues as seen with earlier centerline alignments.

 
 

The evolution of wheel alignment: 1978 - Present

 
 

Total four-wheel alignment for vehicles with adjustable rear wheels

The growing popularity and population of vehicles with independent rear suspensions and front-wheel-drive systems took thrustline alignment to the next level.

Total four-wheel alignment evolved to service vehicles with adjustable rear wheels to correct rear individual toe (thrustline) before adjusting front individual toe.

Measuring and adjusting rear toe to the preferred specification sets the thrustline parallel with the geometric centerline of the vehicle. The steering wheel is leveled and then front individual toe is adjusted to the current thrustline.

Total four-wheel alignment allowed the technician to finish the alignment with a level steering wheel and set the vehicle body to travel straight in line with all four wheels, extending tire life and eliminating dogtracking.

 
 

The evolution continues...

 
 

Steering angle sensor reset: The new last step in alignment service

Until recently, a total four-wheel alignment was considered complete once the technician finished adjusting front toe. With all four wheels set to specification (pointing straight with the thrustline of the vehicle) and a level steering wheel, the technician had accomplished the objective and was ready to move on to the next job. However, for millions of vehicles equipped with Steering Angle Sensors, this is no longer true.

A growing number of OEMs now require Steering Angle Sensor reset in conjunction with alignment service.

Alignment corrects mechanical adjustments, but the SAS requires an electronic reset to match the vehicle's new thrustline. The actual position of the SAS is unknown after an alignment, which is why measuring and resetting the SAS is now the new last step of alignment service.

Failure to perform SAS reset when required can affect the proper operation of electronic driver-assist systems that rely on precise steering information from the SAS. Shops unfamiliar with SAS reset face new challenges and questions of how to properly align vehicles with SAS.

Alignment questions for vehicles with SAS:

• Is this vehicle equipped with SAS?
• Does this vehicle require SAS reset?
• How do I reset SAS on this vehicle?
• What tool do I use?
• How do use this tool?
• How do I document SAS reset was complete?

 
 

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