Lesson 1: What is Hydraulic Steering?


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Lesson 1: What is Hydraulic Steering?

As off-road driving enthusiasts or competitors, we all go through a natural progression of mechanical mayhem as we rise through the ranks in the world of off-road motorsports. From trail riding to technical rock crawling, off-road racing, or monster trucking, we see how high we can kick up the mud or dust and chase our vehicle's weak links with upgrades that will allow us tackle that next rock ledge, conquer that next hill climb, or win that next race with more finesse and/or speed than before. 

Bigger tires, stronger axles, and more power... these are the items that quickly rise to the top of every driver's list of must haves. And while steering upgrades might not seem as glamorous of an investment as a powerful new motor or shiny new wheels, there are few other vehicle upgrades that can so significantly influence whether your off-road driving experience is an enjoyable or a miserable one. 

The Steering Evolution

Perhaps you have heard it called hydraulic steering, hydro steering, or full hydro. No matter what you call it, a fully hydraulic steering system offers the ultimate steering platform for the most extreme off-road drivers. Benefits include:

  • Easy steering of large, heavy tires
  • Suspension and chassis design freedom
  • High strength to handle abusive driving environments
  • Compact installation
  • Tunable performance
  • Rear steer capability
  • Did I mention suspension and chassis design freedom?!

    Compared to most of the technological advancements introduced to the off-road industry over the past decade, hydraulic steering technology has changed relatively little since it's adoption in agriculture and heavy machinery dating back to the 1960's.

    While the concept is tried and true, the application of hydraulic steering in the off-road motorsports venue, applied improperly, can quickly strain the limits of equipment capability and just as every off-road vehicle and intended use is unique, so is the ideal steering system configuration. Although there are many full hydro "kits” on the market, there is no one-size-fits all solution which makes it so important to understand the basics of system design and to consult a professional, when needed, that can help you size and select the most appropriate components for your vehicle.

    Whether you are new to the concept of hydraulic steering or a seasoned off-road veteran wanting to brush up on the basics, this tech series will take a top-level look at the fundamentals of hydraulic steering. So, let’s get started!

    Steering Types

    In order to truly understand hydraulic steering, we need to start with the basics. For our needs in the off-road world, we can generally lump different steering systems into one of three categories:

    • Power Steering
    • Hydro Assist Power Steering
    • Fully Hydraulic (Full Hydro) Steering

    Important to keep in mind is that any good steering system serves two important functions; it provides enough force to steer a vehicle with reasonable input effort from the driver and it controls the position of the steering such that operating a motor vehicle is predictable and safe.

    Power Steering

    If we consider only OEM vehicles with solid front axles for the moment, they almost exclusively feature a mechanical steering gearbox mounted on the vehicle chassis that converts the rotational motion of the steering wheel into a linear motion which in turn forces the tires to steer left or right.

    In these traditional power steering systems, a steering pump supplies pressurized oil to the steering box to hydraulically generate additional steering force for a given amount of driver effort applied through the steering wheel. In other words, this makes the steering wheel feel easier to turn.

    These systems have limitations in terms of the steering force that they can generate and because they feature a mechanical linkage between chassis and axle, the steering box and steering linkages need to be positioned such that they work with the vehicle suspension to avoid dangerous bump steer.

    Hydro Assist Steering

    As the need for stronger steering becomes evident with increasingly large tire sizes and rough terrain, you may also hear the term hydraulic assist or hydro assist thrown around as an option for increasing steering force.

    This type of setup involves drilling and tapping into the steering box and plumbing the pressurized fluid from the existing power steering system to a hydraulic cylinder, also called a ram, connected between the axle housing and tie rod. When turning, the hydraulic cylinder generates assistive steering force while the steering box continues to control the steering position of the tires through a mechanical linkage (drag link).

    While hydro assist can help produce the force needed to steer big tires in rough terrain, suspension and chassis design is still limited due to the required mechanical steering linkage between chassis and axle. This is where full hydro comes in for those wanting to achieve the most extreme off-road performance.

    Full Hydro Steering

    In a fully hydraulic steering system, control of both steering force and steering position relies 100% on fluid power which is plumbed through flexible hoses. This means that there is no longer a mechanical steering linkage between the chassis and axle which opens up options for more advanced truck and buggy suspension and chassis designs.

    A power steering system is technically a hydraulic system and as such, many aspects of the hydraulic circuit in a power steering system are also applicable to a full hydro steering system.

    In fact, the only fundamental difference between power steering and full hydro is that with full hydro, the steering box is replaced by a steering control valve, often referred to as an orbital valve, which precisely controls the volume of steering fluid supplied to a hydraulic steering cylinder mounted on the axle.

    Of course, if one were to simply replace their steering box with a steering control valve and plumb it to a hydraulic cylinder without any other upgrades, they would surely be disappointed with the resulting performance. You see, over the years of operating vehicles that have evolved over the past century to use the same fundamental methods of control, we have become accustomed to a certain vehicle response when we input force into a steering wheel. You could say that we have developed an automatic expectation within our genetic code. 

    The challenge lies in the fact that for a fully hydraulic steering system to deliver a vehicle response that meets these physiological expectations generally requires significantly higher pressure and flow rate than is demanded by a traditional power steering system with mechanical steering gearbox. 

    Higher pressures and flows translate to greater energy consumption and heat generation compared to a traditional power steering system. Without careful planning, these factors can lead to cavitation, steering fluid breakdown, pressure spikes, and a host of other issues that can damage steering pumps and valves. For this reason, successful implementation of hydraulic steering requires careful balancing of steering performance needs with system capabilities.

    Add in the fact that off-road vehicles are reaching faster speeds and tackling bigger obstacles than ever before and it’s easy to see why hydraulic steering systems are often one of the most troublesome and misunderstood vehicle systems in the off-road world.

    But fear not, because with just a bit of engineering and understanding of hydraulic systems, a properly designed full hydro steering arrangement can yield performance and reliability rival to the best mechanical steering systems out there while also providing steering force and vehicle design freedom that can’t be matched.

    Whether you drive a mildly built jeep, tube buggy, rock crawler, rock bouncer, desert racer, mega truck, or monster truck, the same basic principles are applied to help you get the best driving experience out of your vehicle.

    So stick around because this series of Hydro Steering 101 articles will cover all of the details that you need to know. Stay up to date on the latest articles by signing up for Radial News below and following @RadialDynamics on Facebook and Instagram. In the meantime, if you need help with upgrading or building a new steering system, you can always reach out for a steering solution as unique as your ride. Thanks for tuning in!


    About the Author

    Eric Amato

    Eric received his Bachelor's in Mechanical Engineering from Umass Amherst in 2008 and has since dedicated his career to fluid mechanics. Today, he is a full-time manager of industrial spray systems and fabrications in addition to being owner and engineer of Radial Dynamics. In his free time, you can find him either racing his buggy, traveling, practicing photography, or working with his wife on their apple orchard in western Massachusetts.