What Are the Different Types of Steering Knuckle?

Ever wondered what that chunky piece of metal is that your wheel bolts onto? That’s the steering knuckle, and its design varies significantly depending on your car’s suspension system.

The two primary types of steering knuckles are the conventional design used in double wishbone suspensions, and the MacPherson strut knuckle, designed for strut-based systems. Other variations exist for rear axles and complex multi-link setups.

The steering knuckle is a crucial, load-bearing component that acts as the central hub for your vehicle’s steering and suspension systems. It’s the critical link to which nearly everything attaches: the suspension arms, the strut or shock absorber, the steering linkage, the brake caliper, and the wheel hub itself. As a specialist manufacturer of automotive parts for over 25 years, we at GSW Autoparts know that the design of this single part dictates the entire architecture of the suspension. Let’s explore the main types you’ll encounter.

What Is a Steering Knuckle?

Before we get into the different types, let’s first establish exactly what a steering knuckle is and what it does.

A steering knuckle is a solid component, typically made of cast iron or forged aluminium, that houses the wheel hub or spindle and connects the suspension and steering components to the wheel. It is the pivot point on which the wheel turns.

From our perspective as parts manufacturers, we see the steering knuckle as the ultimate multi-tasker of the chassis. It has several critical mounting points and functions:

• Wheel Hub Mounting: It has a large, precisely machined hole in the centre where the wheel hub and bearing assembly is mounted, allowing the wheel to spin freely.
• Suspension Pivot: It provides attachment points for the outer ends of the control arms (via ball joints) or the strut. This allows the wheel to move up and down with the road surface.
• Steering Input: It has an arm or mounting point for the tie rod end. When you turn your steering wheel, the tie rod pushes or pulls on this arm, causing the entire knuckle assembly to pivot, thus steering the vehicle.
• Brake Mounting: The brake caliper¹ is bolted directly onto the steering knuckle², positioning it correctly over the brake disc.

Without the steering knuckle, there would be no way to connect all these vital systems together. It is the cornerstone that ties the wheel to the car.

What are the different types of steering knuckle?

While all knuckles perform the same core function, their shape and design change dramatically to suit the type of suspension system they are part of.

The two main types of steering knuckles are the conventional type for double wishbone (SLA) suspensions and the MacPherson strut knuckle. Each is designed to accommodate a fundamentally different suspension geometry and component layout.

As a comprehensive supplier, we at GSW Autoparts provide parts that interact with both of these primary designs. Understanding them is key to understanding modern suspension.

1. Conventional Steering Knuckle

This is the traditional design found in suspension systems that use both an upper and a lower control arm, known as a double wishbone or Short-Long Arm (SLA) suspension.

Its key feature is that it has two distinct pivot points for ball joints, one at the top and one at the bottom. The upper control arm’s ball joint connects to the top of the knuckle, and the lower control arm’s ball joint connects to the bottom. This creates a very stable and precisely controlled "box" geometry. The shock absorber and spring are typically mounted separately, connecting to the chassis and one of the control arms (usually the lower one). This design allows for excellent control over wheel geometry (like camber angle), which is why it’s favoured in performance cars, heavy-duty trucks, and racing applications.

2. MacPherson Strut Knuckle

This is the most common type found on the front suspension of the vast majority of modern passenger cars in the UK and worldwide. It is designed specifically for the space-saving and cost-effective MacPherson strut suspension.

The most obvious difference is that it does not have a mounting point for an upper control arm. Instead, it features a large, heavy-duty integrated bracket on its side. The body of the strut assembly slides into this bracket and is secured with one or two large pinch bolts. In this system, the strut itself acts as the upper locating link and steering pivot. The knuckle still has a mounting point at the bottom for the lower control arm’s ball joint. This design is less complex and lighter than a double wishbone setup, making it ideal for most everyday vehicles.

Other Variations You Might Encounter

Beyond the two primary front suspension types, there are other variations and related components you might come across.

Other variations include rear knuckles, often called hub carriers or spindles, which don’t steer, as well as complex knuckles for multi-link suspensions with numerous mounting points. Materials also vary, from cast iron to lightweight forged aluminium.

From our broad manufacturing experience, we know the knuckle family is quite diverse:

• Rear Knuckles (Hub Carriers): On vehicles with independent rear suspension, you’ll find a similar component at the back. Since the rear wheels don’t steer, it’s not technically a "steering" knuckle. It’s often called a hub carrier or rear spindle. Its job is to hold the rear wheel hub/bearing and provide mounting points for the rear suspension links or arms and the rear brake caliper.
• Multi-Link Suspension Knuckles: Modern, complex multi-link suspensions (often found on premium German or Japanese cars) can have knuckles that look incredibly intricate. Instead of just one or two control arm mounting points, they may have three, four, or even five separate mounting bosses for the various links that control toe, camber, and other dynamics.
• Material Differences: While most standard vehicles use strong and cost-effective cast iron for their knuckles, many performance and luxury vehicles use forged aluminium. Aluminium knuckles are significantly lighter, which reduces the vehicle’s "unsprung weight" (the weight of everything not supported by the springs). This allows the suspension to react more quickly to bumps, improving both ride quality and handling.

How to Identify Different Types of Steering Knuckles

If you look behind your car’s wheel, how can you tell what type of steering knuckle you have? The answer lies in identifying the components connected to it.

To identify a steering knuckle type, look at what connects to it. If a large, tube-like strut is bolted to the side of the knuckle, it’s a MacPherson strut system. If you see distinct upper and lower A-shaped arms connecting to the top and bottom of the knuckle, it’s a conventional/double wishbone system.

Here’s a practical guide for any aspiring mechanic or curious car owner. Safely look behind one of your front wheels (you may need to turn the steering to get a better view).

1. Look for a Strut: The most obvious tell-tale sign of a MacPherson strut knuckle³ is the strut itself. You will see a large, vertical, tube-like assembly that houses the spring. Follow it down, and you will see it bolts directly and rigidly into a bracket on the side of the steering knuckle. You will also only see a single control arm (a lower one) at the bottom. I’d say this accounts for a huge percentage of cars I’ve seen in UK garages.

2. Look for Two Control Arms: If you do not see a large strut bolted to the knuckle, look instead for two separate arms. You will see a lower control arm⁴ connecting to the bottom of the knuckle via a ball joint. Then, look above the brake disc and axle. If you see another, often smaller, upper control arm⁵ connecting to the top of the knuckle, then you have a conventional knuckle as part of a double wishbone suspension. This is a clear indicator of a more performance-oriented suspension design.

By identifying these key connecting components, you can quickly determine the type of steering knuckle and suspension system your vehicle uses.

Conclusion

The steering knuckle is a cornerstone of your vehicle’s chassis, and its design dictates the type of suspension system used. Understanding the difference between conventional and MacPherson strut knuckles is key to understanding modern vehicle dynamics.