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How Steering Works

The driver's link to the road

Back when we were kids, we were happy to steer our home-built go-karts with a piece of rope. Add a few decades of personal driving experience, a few thousand pounds of metal and a lot more speed, and suddenly the issue of vehicle steering becomes far more critical. Making a modern automobile answer a driver's fingertip commands takes a significant amount of technology.

Road Feel

Boiled down to its basics, your vehicle's steering system must carry your steering inputs to the front wheels faithfully and with a minimum of play, regardless of suspension motion or power application. And the connection between your hands and the wheels needs to be a two-way street. Not only are you sending sometimes subtle commands to the front wheels, you are also continuously receiving useful feedback through the steering wheel that can tell you a lot about the car's situation. It's the quality and nuance of this feedback that separates a BMW M5 from a clapped-out New York City taxi. (There are a few other differences, of course, but we won't get into them now.)

The mechanics of this critical control system don't vary much in concept from vehicle to vehicle. To start at the beginning, the steering wheel is mounted on the end of a shaft that passes through the front wall of the passenger compartment (typically called the firewall). Along the way, it incorporates a telescoping mechanism designed to allow the steering column to collapse in the event of a crash—a major advance from the days when old rigid steering shafts would harpoon the hapless driver like an unlucky sea creature.

The steering shaft's forward end fits into a steering gearbox, where the rotary motion of the steering shaft is converted into lateral motion. Links called tie-rods carry this lateral motion outboard to the front wheels, where they are connected to short arms on the pivoting spindles that carry the front wheels. All but the lightest and/or cheapest cars have some sort of power steering system, which is designed to keep the effort at the steering wheel down to a comfortable level. Even if the power steering system should fail, the driver still has a direct mechanical connection to the wheels that makes it possible to steer—but it takes some serious muscle (thus the old "armstrong steering" cliché).

Rack or Ball?

Steering systems seem pretty straightforward, but the details of the execution burn up tremendous engineering time and effort. Take for example the different types of steering gear. Rack-and-pinion and recirculating-ball are among the most common steering-gear types used to convert the rotary motion of the steering wheel into the lateral motion that actually controls the wheels. In current-day vehicles, the detail design and engineering seem to have greater effects on the performance of the steering than does the basic steering-gear type.

Many factors influence a car's handling—far more than we can do justice to here. The design of the front suspension and the specs of the wheel placement are critically important, as is the angle of the steering axis of each wheel, which affects stability and cornering power. Friction and play in the steering system must be kept to an absolute minimum. The design of the driveshafts in front-drive cars also can come into play, since the application of engine power can cause the steering to pull to one side (torque steer is the common term).

Even the design and performance of the power steering system plays a large role in the handling quality of a car. Most of these systems use engine power to drive a pump that uses pressurized fluid to magnify your steering effort. Some other systems are all-electric, using electromagnetic force to help do the work of steering. Regardless of the type of system, power steering is engineered to assist without completely robbing the steering of its communicative "feel." Success on this front varies widely, with some cars delivering a lively, responsive feel combined with acceptably low physical steering effort. Some others simply feel numb. Either way, the vehicle may be quite controllable, but there's no question that more communicative steering makes driving more fun.

Steering engineers are perpetually at work on this challenge, working with chassis engineers to help reduce bad traits and enhance good ones. Some types of feedback like excess road vibration and sharp kickback through the steering on bumps are unwelcome, while subtle changes in steering effort that indicate that the front tires are losing their grip in a corner or are starting to hydroplane are critically important. A car's "on-center" steering feel is a big part of its perceived stability and controllability. "Turn-in" is another phrase you'll hear batted around in road-test copy, and describes the way a vehicle turns into a corner. Assessing steering character is like wine-tasting—which explains why there is no clear consensus about what car steers best.

Car Care

Maintenance requirements with modern steering systems are relatively minor. You need to maintain the power steering fluid level and have the various rubber boots that protect moving parts inspected on a regular basis (listed in your owner's manual). Power steering hoses and fittings need to be inspected regularly too. Wheel alignment, wheel balance and suspension damper (a.k.a. shock-absorber) wear also weigh heavily on steering quality and accuracy. Unusual vibration, consistent pulling to one side, clunking or popping sounds or a steering wheel that doesn't aim straight ahead when the car is traveling straight are all signs that its time for a visit to a dealer, mechanic or alignment shop.

With the complexity and sophistication of modern steering systems, the days when any steering problem can be fixed with a new piece of rope are long gone.