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How Your Car's Steering Works

Alex Palmeri
August 8, 2018

Looking into the future, there may come a day when you won’t need to steer your car — it’ll do it all itself. But even if vehicles eventually come without a steering wheel, they’ll still require a steering system.  

These systems have evolved dramatically over the last few decades, and in this article, we’ll cover the different types of steering systems, their components, methods of power steering, alignment angles, and how this all works together to keep you pointed in the right direction.

Steering basics 

At its core, a steering system takes the rotational force created when you turn the steering wheel and converts it into a swiveling movement of the front wheels. Let’s look at simplified example.

A go-kart has the most basic steering system, with a shaft pointed down between the wheels. Connected to a small arm on the bottom of the shaft are tie rods going out to each wheel. These three simple pieces turn the spindles, which the spinning wheels are connected to.

In your car, the steering wheel is attached to the steering column, which in turn is attached to a steering gear. This gear moves the pitman arm, a part that connects to the drag link and tie rods — metal pieces that go out to the spindles, which the front wheels are mounted on.

When you turn your steering wheel, you rotate a shaft inside the steering column and thus move the steering gear. The gear is what transfers the rotation of the wheel into a side-to-side motion of the steering linkage. 

Because your wheels and tires are connected to the spindles, they move when the linkage pushes or pulls the spindles in and out. Universal joints are used between the steering column and gear box or rack, and ball joints are used between the gear box or rack and the spindle. This allows the spindle to move up and down, as well as turn right and left, while maintaining acceptable alignment and steering control. 

Now let’s look more specifically at different types of steering systems, and how they work. 

Rack-and-pinion steering

Most cars and trucks use a rack-and-pinion steering system. This simple yet effective system consists of a rack — a horizontal piece of metal with teeth on one side — and a pinion gear — a round gear with teeth that interlock with the rack — set inside a tube.

In the diagram at right, when you turn the wheel (1), the steering shaft (2) turns, as does the pinion gear (3) on the end of it. Tie rods (4) attach to each end of the rack, and move the spindles and wheels (5). 

When you turn the wheel, the gear spins and moves the rack and tie rods. The tie rods are threaded metal rods with ball joints at each end. The threaded, straight end screws directly onto the rack while the end with the right-angle joint is attached to the spindle, allowing the spindle to swivel and move in the desired direction.

The diameter (or number of teeth) on the pinion gear will affect the steering in two ways. A small gear with just a few teeth will make it easier to turn the wheel, but will react slowly, requiring more rotations to make a sharp turn. A larger pinion gear (more teeth) will give a sporty quick turn if you have the muscles to turn it. Heavy cars require power steering because the amount of mechanical advantage offered by a rack and pinion system is limited to the smallest size gear that will move the rack without stripping off the teeth.  

Power-assisted rack-and-pinion

Most vehicles that use rack-and-pinion also use power steering. In this case, there is a cylinder and piston that are connected to the rack. Ports on each side of the piston are connected to the power steering lines. A power steering pump supplies pressurized fluid, and a rotary valve directs the fluid to each line. 

When you turn the wheel, the rotary valve sends more pressure to one side of the piston, providing assistance in that direction. This changes if you turn the opposite direction. The rotary valve maintains equal pressure at the piston when you drive in a straight line. Some systems can vary the amount of pressure based on turning force, vehicle speed, vehicle load and other factors. The result is easy low-speed maneuverability in parking lots, combined with a firm turning effort at highway speeds where oversteering could be dangerous.  

Recirculating-ball steering

Invented before power steering, and used on many older vehicles and large trucks, a recirculating-ball steering system accomplishes the same task as rack-and-pinion but in a different manner, by using a worm gear. Instead of teeth, this type of gear has a sort of spiral running the length of it, like you would see on a bolt.

With this setup, you still have a steering shaft that spins as you turn the steering wheel. But now the shaft is connected to the worm gear, which is inserted into a metal block with gear teeth on one side. The teeth of the metal block mesh together with a sector gear — a gear with teeth on only one side. The sector gear is attached to a pitman arm, a small lever that rotates. When you turn the wheel, the block moves and turns the pitman arm, which is attached to the steering linkage. 

This linkage consists of inner and outer tie rods that attach to the spindles. You will also have a drag link that connects both side tie rods, and an idler arm, another lever that supports the system while also pivoting as you turn the wheel side to side. 

In between the bolt and the treads in the metal block, there are many little ball bearings. These reduce friction and also take up any slack that normally exists between a bolt and threads. This is where the name “recirculating ball” comes from.

Power steering can also be used with a recirculating-ball steering system and works in a very similar fashion to rack-and-pinion. Pressurized power steering fluid is applied to one side of the block, depending on which way you are turning.

Electric power steering

In a never-ending battle to reduce emissions and improve fuel economy, even steering systems are being optimized. In this case, the power steering pump is being replaced with a much more efficient electric motor. 

Electrically assisted power steering uses an electric motor attached to the rack-and-pinion assembly, or directly to the steering shaft. Using various sensors, a computer can detect the direction the driver wants to turn and energize the motor to offer assistance only when needed. 

This eliminates a horsepower-robbing power steering pump that’s continually being spun by the engine. With this style of power steering, the feel and responsiveness can be adjusted on the fly, providing a more accurate and appropriate amount of steering assistance, producing an ideal experience in any driving condition. 

Alignment

With any steering system, geometry and alignment are very important. Without proper alignment, your vehicle may pull to one side, not return to center when finishing a turn, or even steer to one side when hitting a bump. There are three main alignment angles: toe, camber and caster. They affect each other and play a big role in tire wear and handling characteristics. 

Toe: Imagine your two front tires are facing you, so that they could roll toward you. Now imagine someone rotating one or both of the tires so that they would slightly roll toward each other or away from each other. This is toe.

It’s the most common alignment angle that requires adjustment — and it’s adjustable on every car. If it’s not perfect, you’ll begin to notice uneven tire wear. You may also sense the car wandering side to side, feel it pulling to one side, hear a squealing noise when driving or have a steering wheel that rests off center. 

Camber: Again, imagine a tire is facing you, so that it could roll toward you. Now imagine someone standing to the side of the tire pushes or pulls on the top of the tire, so that it tilts vertically. This is camber.

Negative camber refers to the inward tilt of the top of the tire and positive is the outward tilt. Both can be caused by worn out bearings, ball joints or bent spindles can affect camber angles. Bad camber will wear out tires, but not nearly as quickly as improper toe.

Caster: This is the angle of your steering axis when viewed from the side of the car. Imagine the front steering fork on a motorcycle, like at right. It points forward at the bottom and slants backward at the top. This creates positive caster, which helps increase stability when driving straight.

This angle won’t affect tire wear very much, but it will cause your car to feel unstable if not adjusted correctly. Caster usually can’t be adjusted, though. It’s set when the vehicle is built and will typically only change when the car is involved in an accident or with worn steering and suspension components.

How to maintain your steering system

Modern vehicles require very little maintenance when it comes to the steering system. The power steering fluid may require inspection or replacement from time to time — your owner’s manual will provide the specific interval. 

Some older cars have grease fittings on certain steering components, such as tie rod ends, so keeping them lubricated will maintain a smooth steering feel and extend the parts’ service life. 

Also, other vehicles may have steering components that are already threaded for grease fittings, but instead have tiny threaded plugs in the parts from the factory. If you swap out these plugs for grease fittings on your first service, and get them greased at every oil change, these parts will last close to the car’s lifetime.

It’s most important to keep up on your alignment. It should be checked and adjusted if necessary anytime you are replacing tires or if you feel a pull or drift. Consult your owner’s manual for alignment and steering component inspection intervals.

 

Alex Palmeri

About the Author

Alex Palmeri worked nine years as a master technician at Mercedes-Benz of Chicago and is currently the foreman at a large fleet garage. He writes about automotive news, maintenance and racing, and runs a YouTube channel called Legit Street Cars.

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