What is rack and pinion steering?

Most cars, SUVs, and small trucks come equipped with a rack and pinion system that converts the circular motion of the steering wheel into linear motion, causing the wheels to move and turn as required by the driver.

Today on the Sun Transmission blog, we will discuss the rack and pinion system, explaining what it is, how it works, the associated issues, and how to solve them.

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Getting to know the rack and pinion steering system

The rack and pinion system are one of the most used steering systems in vehicles. It consists of a circular gear called the pinion that rotates around its axis and a toothed linear gear called the rack, which moves linearly according to the rotation of the axis.

The operation of a rack and pinion mechanism is similar to simple gears, requiring them to have the same pitch and module. Pitch indicates the number of teeth on the pinion, while the module refers to the size of the teeth.

The rack and pinion system might seem complex, but it is the central component of steering. This mechanism has been used since the 1930s, with BMW manufacturing the first rack and pinion gearbox, though it was Ford's Mustang II in 1974 that first used it in a vehicle.

How does the steering rack work?

In summary, the rack and pinion system perform two basic functions:

• Converts the rotational motion of the steering wheel into linear motion to turn the wheels.
• Reduces the speed of rotation so that the steering wheel can turn the wheels.

The steering wheel and steering column transmit the force applied by the driver to the steering gear, which reduces the steering wheel's rotation speed to transfer the force to the wheel movements.

When the driver turns the steering wheel, the pinion rotates and engages with the rack, causing the wheels to move left or right. This is achieved through tie rods connected to the ends of the rack, responsible for turning the wheels in the desired direction.

The tie rods play a crucial role in transmitting the steering motion from the pinion to the rack and wheels. These tie rods have inner and outer ends; the inner ends are connected to the rack and pinion system, while the outer ends are connected to the steering knuckles.

How does rack and pinion steering work with power steering?

Power steering is integrated into some rack and pinion steering systems to reduce the effort required by the driver to steer the vehicle.

Power steering can be hydraulic or electric. Hydraulic systems use an engine-driven pump to generate hydraulic pressure that assists in the movement of the rack and pinion gears. Electric power steering systems use an electric motor to generate pressure.

It's worth noting that vehicles with power steering have a different rack and pinion design, utilizing two steel tubes beside an electric rack to perform left and right turning functions.

The purpose of power steering is to enhance driving experience, especially at low speeds and during parking maneuvers. It reduces steering effort, adds comfort, ease of driving, and enhances driving safety.

What are steering rack ratios?

In general, the number of teeth on the pinion and the length of the rack determine the rack and pinion steering ratio, indicating how much the steering wheel turns compared to how much the wheels turn. For example, if a 360° turn of the steering wheel results in a 20° turn of the car's wheels, the steering ratio is 18:1, calculated as 360 divided by 20. A higher ratio means less steering wheel movement is needed to turn the wheels, providing a more agile steering feel with greater responsiveness.

Conversely, a lower steering ratio requires more input from the driver to turn the steering wheel, resulting in slower and less responsive steering.

Sports cars typically use a higher steering ratio than cars and trucks because they are lighter and require greater efficiency while ensuring safety during high-speed turns. Vehicles with power steering have optimized steering ratios, increasing reliability and driver safety.

Why is it important for vehicle safety?

Rack and pinion steering is considered safer due to its responsiveness and the precision it allows, especially when paired with power steering.

The direct connection between the steering wheel and the steering system immediately transmits the driver's steering inputs to the wheels, providing a sense of quickness and control that enhances safety for cornering, navigating roads, making tight turns, and parking with precision and safety.

Moreover, rack and pinion steering systems have a compact design, making them suitable for small vehicles with limited space, contributing to better weight distribution and overall vehicle safety, especially in challenging driving situations.

The maneuverability of a vehicle equipped with rack and pinion steering allows for quick lane changes, parking in tight spaces, driving on busy streets, responding promptly to unexpected situations (such as a vehicle suddenly entering the path at high speed), and maintaining stability.

Common problems with rack and pinion steering

Although rack and pinion steering are made of steel, it can develop faults due to continuous vehicle use, repetitive impacts from uneven roads or concrete, or contamination of the transmission flow, carrying sand into the gears. The most common issues include:

Steering wheel vibration

A shaking, vibrating, or wobbling steering wheel indicates issues with the rack and pinion. These problems can occur at any driving speed but are more noticeable on uneven roads.

Hard steering wheel turns

If suddenly it becomes harder to turn the steering wheel, there may be an issue with the rack and pinion. Often, this is due to low pressure from steering fluid leaks or contamination.

Fluid leaks

This problem is exclusive to hydraulic power steering systems, as electric systems do not use steering fluid. These leaks can occur due to deteriorated seals or gaskets, causing stiff steering, overheating of the rack, and gear failure.

Squealing noise

If there are fluid leaks, you might notice a burnt smell and a squealing noise while driving, caused by metal rubbing. This noise is particularly noticeable during steering.

Wandering steering

Wandering steering is a safety issue, making it difficult to drive straight and control the vehicle for turns.

Seek advice on obtaining rack and pinion steering

As you can see, the rack and pinion system are widely used in modern cars to enhance driving experience and safety during turns and maneuvers.