Subaru Wheel Alignment: The Ultimate Guide

Ensuring your Subaru is tracking straight and true is paramount for a safe and enjoyable driving experience. Wheel alignment, often overlooked until problems arise, plays a critical role in your vehicle's handling, tyre wear, and overall efficiency. This comprehensive guide will delve into the intricacies of measuring and understanding Subaru wheel alignment, covering the essential checks and procedures that keep your car performing at its best.

Why Wheel Alignment Matters for Your Subaru

A proper wheel alignment is more than just a routine check; it's fundamental to your Subaru's longevity and your driving pleasure. Misaligned wheels can lead to a host of issues, including:

• Uneven Tyre Wear: This is perhaps the most common and noticeable symptom. If your wheels aren't pointing in the correct direction, your tyres will scrub against the road surface, leading to premature and irregular wear patterns. You might see feathering, cupping, or excessive wear on the edges of your tyres.
• Poor Handling and Steering: A misaligned Subaru can feel 'floaty' or 'darty' on the road, pulling to one side or feeling unstable, especially at higher speeds or during cornering. This can make steering feel heavy or imprecise, reducing your confidence behind the wheel.
• Increased Fuel Consumption: When your wheels are fighting against each other, your engine has to work harder to maintain momentum, leading to a noticeable drop in fuel economy.
• Stress on Suspension Components: Constant misalignment puts undue stress on various suspension parts, such as ball joints, tie rod ends, and bushings, potentially leading to premature failure and costly repairs.

When Should You Check Your Subaru's Wheel Alignment?

Subaru recommends inspecting your wheel alignment at regular intervals to preemptively address any issues. The general guideline is:

• Every 30 months or 30,000 miles, whichever comes first.

However, certain driving conditions can necessitate more frequent checks:

• Winter Driving: The presence of potholes, kerbs, and general road debris common in winter can easily knock your alignment out. If you frequently encounter these conditions, consider checking your alignment more often, perhaps seasonally.
• After Impact: If your Subaru has been involved in an accident, even a minor one, or has hit a significant pothole or kerb, it's wise to have the alignment checked immediately.
• New Tyres: It's good practice to check the alignment whenever you fit new tyres to ensure they wear evenly from the outset.
• Steering or Suspension Work: Any work carried out on the steering or suspension system should always be followed by a wheel alignment check.

Key Components of Subaru Wheel Alignment Measurement

Measuring wheel alignment involves a series of precise checks of various angles and distances. Here are the key parameters you'll encounter when checking a Subaru:

1. Wheel Arch Height (Vehicle Ride Height)

Before diving into the alignment angles, it's crucial to ensure the vehicle's ride height is correct. This is measured from the ground to a specific point on the wheel arch. An incorrect ride height can influence the alignment readings. To measure wheel arch height accurately:

1. Adjust Tyre Pressures: Ensure all tyres are inflated to the manufacturer's specified pressures. This is a fundamental step for any accurate measurement.
2. Load the Vehicle: The vehicle should be at 'curb weight'. This means it should have the spare tyre, jack, and any essential tools on board, and the fuel tank should be topped up. The steering wheel should be in a neutral, forward position.
3. Measure from Arch to Ground: A common method involves suspending a plumb bob (a weighted string) from a reference point on the wheel arch (often labelled 'A' in workshop manuals). This string will hang directly above the centre of the wheel spindle.
4. Determine the Spindle Centre: The centre of the spindle (the axle hub) is the reference point for many alignment measurements.
5. Measure the Distance: Measure the distance from the point directly below the suspended thread (above the spindle centre) to the centre of the spindle. Alternatively, measure the distance from the ground to the wheel arch at a designated point.
6. Consult the Service Manual: Always refer to your Subaru's specific service manual for the exact measurement points and the acceptable range for wheel arch height.

2. Camber (Front and Rear)

Camber is the angle of the wheel relative to the vertical plane when viewed from the front or rear of the vehicle.

• Positive Camber: The top of the wheel tilts outwards.
• Negative Camber: The top of the wheel tilts inwards.
• Zero Camber: The wheel is perfectly vertical.

Correct camber is vital for tyre contact with the road during cornering and for straight-line stability. Excessive positive or negative camber will cause rapid tyre wear on the inner or outer edge, respectively.

3. Caster (Front)

Caster refers to the angle of the steering axis (the line through the pivot points of the steering system) relative to the vertical plane when viewed from the side.

• Positive Caster: The steering axis is tilted backward towards the rear of the vehicle.
• Negative Caster: The steering axis is tilted forward towards the front of the vehicle.

Caster significantly influences steering stability and the self-centring action of the steering wheel. Proper caster helps the wheels return to the straight-ahead position after a turn and contributes to a stable feel on the motorway.

4. Toe-in (Front and Rear)

Toe is the angle of the wheels relative to the vehicle's longitudinal axis when viewed from above.

• Toe-in: The front edges of the wheels are closer together than the rear edges.
• Toe-out: The front edges of the wheels are further apart than the rear edges.

Toe settings are critical for tyre wear and directional stability. Too much toe-in or toe-out can cause the tyres to scrub sideways as the vehicle moves, leading to rapid wear and poor handling. Front toe is often adjustable, while rear toe may also be adjustable depending on the Subaru model.

5. Thrust Angle (Rear)

The thrust angle is the angle of the rear axle relative to the vehicle's longitudinal centreline. Ideally, the thrust angle should be zero, meaning the rear axle is perfectly perpendicular to the vehicle's centreline.

An incorrect thrust angle indicates that the rear axle is not aligned correctly with the vehicle's direction of travel. This can cause the vehicle to 'dogleg' or pull to one side, even if the front wheels are aligned. It's a key indicator that there might be underlying structural or suspension damage at the rear.

6. Wheel Steering Angle

This measurement relates to the steering system's geometry, particularly how the wheels turn in relation to each other when the steering wheel is turned. Modern alignment equipment can measure the 'ackermann' or 'dynamic' steering geometry, ensuring that as you turn, the inner wheel turns at a sharper angle than the outer wheel. This prevents tyre scrub during cornering.

The Wheel Alignment Measurement Process

Professional wheel alignment is performed using sophisticated equipment that measures all the angles mentioned above with high precision. The typical process involves:

1. Vehicle Preparation: As mentioned, tyre pressures are set, and the vehicle is loaded to curb weight. The steering wheel is centred.
2. Mounting Sensors: Special electronic sensors (or 'targets') are attached to each wheel. These sensors communicate wirelessly or via cables with a central computer.
3. Calibration: The alignment rack and sensors are calibrated to ensure accuracy.
4. Initial Readings: The equipment takes initial measurements of camber, caster, toe, and thrust angle for all wheels.
5. Comparison to Specifications: These readings are compared against the manufacturer's specifications for your specific Subaru model and year.
6. Adjustments: If any angles are outside the acceptable range, adjustments are made. This typically involves adjusting tie rods for toe, and sometimes eccentric bolts or shims for camber and caster, depending on the Subaru model's suspension design. Rear adjustments can vary significantly by model.
7. Re-measurement: After adjustments are made, the readings are re-checked to confirm they are within specification.
8. Test Drive: A short test drive is often performed to ensure the steering feels correct and the vehicle tracks straight.

Common Subaru Alignment Adjustments

The adjustability of alignment angles varies by Subaru model and year. Generally:

• Front Toe: Almost always adjustable via the tie rod ends.
• Front Camber: May be adjustable on some models via eccentric bolts on the lower control arms or by using shims. If not directly adjustable, correcting significant camber issues might require replacing suspension components.
• Front Caster: Often adjustable on many Subaru models, usually through eccentric bolts or by repositioning suspension components.
• Rear Toe: Adjustable on many Subaru models, typically via eccentric cams or bolts in the rear suspension linkage.
• Rear Camber: May be adjustable on some models, often through eccentric cams or shims. In many cases, rear camber is not adjustable and is considered 'fixed', meaning any deviation indicates a bent component or damage.

Checking Suspension Components

During an alignment inspection, it's crucial to check for obvious signs of damage to suspension components. This includes:

• Worn Ball Joints: Excessive play can affect alignment.
• Loose Tie Rod Ends: Crucial for steering accuracy.
• Damaged Bushings: Rubber bushings in control arms and other suspension links can degrade, leading to unwanted movement and alignment changes.
• Bent Control Arms or Links: Any impact can bend suspension components, altering alignment angles.
• Tightness of Bolts and Nuts: Ensure all suspension and steering bolts are torqued correctly.
• Condition of Other Under-Car Components: Check for leaks, worn driveshafts, or damaged exhaust systems that could affect vehicle dynamics.

Frequently Asked Questions about Subaru Wheel Alignment

Q1: How often should I get my Subaru's wheel alignment checked?

A: As a general rule, every 30 months or 30,000 miles. However, it's recommended more frequently if you drive in harsh conditions, after hitting a pothole, or after suspension work.

Q2: Can I check wheel alignment myself?

A: While you can check for obvious signs of wear or pulling, precise measurement requires specialized equipment and a level surface. For accurate alignment, professional servicing is recommended.

Q3: What are the symptoms of a misaligned Subaru?

A: Common symptoms include the car pulling to one side, uneven tyre wear (especially on the edges), a steering wheel that isn't centred when driving straight, and a feeling of instability.

Q4: Does hitting a pothole affect wheel alignment?

A: Yes, a significant impact with a pothole can easily knock your wheel alignment out of specification, leading to the symptoms mentioned above.

Q5: How long does a wheel alignment take?

A: A standard wheel alignment typically takes between 45 minutes to 1.5 hours, depending on the vehicle and the extent of adjustments needed.

Conclusion

Maintaining the correct wheel alignment on your Subaru is a crucial aspect of vehicle upkeep. By understanding the key measurements – wheel arch height, camber, caster, toe, and thrust angle – and being aware of when to have these checked, you can significantly extend the life of your tyres, improve your Subaru's handling and fuel efficiency, and ensure a safer driving experience. Regular inspections and prompt adjustments are the keys to keeping your Subaru performing optimally on all terrains.