What Is Thrust Angle and How Does It Affect Wheel Alignment?

Proper wheel alignment prevents uneven tire wear and damage, keeping the ride smooth and safe. However, various issues can push the suspension out of alignment. One of the ways mechanics check for what’s causing the issue is to determine the thrust angle.

What Is a Thrust Angle?

Thrust angle refers to the rear wheels’ angle based on the total rear toe. It’s the same as the vehicle’s geometric centerline when both rear wheels have zero toe.

The rear toe setting’s total dictates the thrust line, which is the direction the rear wheels are facing.

Determining the thrust angle involves examining the front and rear axles. Ideally, they should be parallel, and a straight line from the rear axle’s center would intersect in the same spot as the front axle.

The ideal thrust angle is when the rear wheels are pushing and pulling in the same direction as the front wheel, ensuring the vehicle moves straight forward.

What Is an Acceptable Thrust Angle?

A zero-degree thrust angle or when the center line is 90 degrees from the rear axle is ideal. Anything over zero is too much.

What Happens When Thrust Angle Alignment Is Off?

An improper thrust angle causes alignment issues, which could result in the following:

Pulling

A pull is when you feel a tug on the steering wheel when driving, usually due to excessive tire wear.

Leading or Drifting

Leading or drifting is when the vehicle mildly veers to one side while driving without affecting the steering wheel.

Wander

Wander is when you need to constantly correct the alignment using the steering wheel to keep your vehicle moving straight.

Off-Centered Steering Wheel

An improper thrust angle crooks the steering wheel because the front wheels steer to align themselves with the direction of the vehicle.

Dog-Tracking

Dog-tracking is when the vehicle’s body is crooked compared to the direction the vehicle is moving to. It creates unequal left or right turning and increases the wear on tires.

What Causes Changes in the Thrust Angle?

Collision or crash impact usually alters thrust angle. It causes the rear axle and related components to misalign. Similarly, improper repair in the rear of the vehicle may also cause it the misalignment.

Incorrect toe setting can also misalign the thrust angle. The toe settings tend to change over time, usually due to impacts from potholes and curbs.

As such, it’s recommended to have your car’s alignment checked annually.

Improper repair in the rear of the vehicle may also cause it the misalignment.

–Anthony Harlin, ASE Certified Master Automobile Technician

What Does Thrust Angle Measurement Entail?

A four-wheel alignment is the most accurate method of checking the vehicle’s thrust angle. It involves adjusting the rear wheels equally so that they point to the vehicle’s geometric centerline. 

Mechanics usually adjust the following when they do four-wheel alignment:

• Rear camber
• Rear toe to reduce the thrust angle near zero
• Front camber and caster

Front toe to ensure the steering wheel is in the straight-ahead position

Experts usually only do four-wheel alignment if the vehicle has an adjustable rear suspension.

A Closer Look at Thrust Angle Correction

There are two ways to correct a misaligned thrust angle: thrust line alignment and toe adjustment.

Thrust Line Alignment

Thrust line alignment sets the front toe parallel with the rear-wheel toe. It works for vehicles with non-adjustable rear suspension. Otherwise, mechanics perform a four-wheel alignment instead.

If the rear toe angles don’t total zero, a thrust condition exists, causing the front wheel steering to match the condition. It could also lead to a crooked steering wheel.

Toe Adjustment

Toe alignment is the extent to which the tires turn inward or outward, as viewed from above.

Mechanics perform toe adjustments to correct the alignment and adjust the thrust angle. They change the rear toes with an eccentric cam or an adjustable tie rod end.

How Much Does Thrust Angle Correction Cost?

Thrust-angle alignment can cost between $50 and $80, while four-wheel alignment services start at $90. Meanwhile, toe alignment services range from $50 to $170.

Closing Thoughts

Incorrect thrust angle and wheel alignment can cause suspension problems that accelerate tire wear and make it risky to drive. So don’t ignore the warning flags. If you encounter symptoms of a misaligned thrust angle, it’s best to have your vehicle checked at an auto repair shop immediately.