Cars · Lesson 9 of 15Intermediate5 min read

Steering, Suspension and Alignment

The suspension keeps the tires pressed to the road while the body rides smoothly over bumps, and the steering points the front wheels where you want to go. Alignment is the set of small angles that makes it all track straight.

Springs and shocks

Springs hold the car up and let the wheels move over bumps without lifting the body. Most cars use coil springs; trucks often use leaf springs, stacked strips of spring steel, and some vehicles use torsion bars, steel rods that twist.

A spring alone would keep bouncing after every bump. A shock absorber stops that: as the wheel moves, a piston forces hydraulic fluid through small openings, which slows the motion and turns the bouncing energy into heat. Coil springs have almost no friction of their own, so they always need shocks. Worn shocks or other suspension parts make the ride bouncy and cornering poor.

Arms, joints and bars

Control arms hold the wheel’s steering knuckle and let it move up and down; rubber bushings at their inner ends act as bearings. Ball joints at the outer ends are swivels that let the knuckle move up and down and turn for steering. Many cars use a MacPherson strut, which combines the shock absorber and coil spring in one unit, so only a lower control arm and the strut hold the front wheel. A stabilizer bar, or sway bar, links the two sides and twists to limit body roll in turns.

Seen from the front of the car, driver’s side. Source: U.S. Navy Construction Mechanic Basic, Chapter 14.

Steering

Many cars use rack-and-pinion steering. A small pinion gear on the end of the steering shaft meshes with a long toothed bar, the rack. Turning the wheel slides the rack side to side, and tie rods at its ends push and pull the steering arms on the knuckles. The gearing multiplies your effort: in one example from the Navy’s mechanic course, 10 pounds on the steering wheel can produce up to 270 pounds at the wheels.

Power steering adds more help. Hydraulic systems use an engine-driven pump, and their pressure can exceed 1,000 psi. Electric power steering uses a motor and a torque sensor instead, and the motor works only when you’re steering, which saves energy. It also drops the pump, hoses, fluid and drive belt.

Alignment: camber, caster and toe

Camber is the tilt of the wheel seen from the front: top out is positive, top in is negative. Incorrect camber wears the tire smoothly on one side, and the car leads toward the side with more camber.
Caster is the tilt of the steering axis seen from the side; top tilted back is positive. Positive caster helps the steering return to center and keeps the car stable, like the wheels of a shopping cart trailing behind their pivots. Uneven caster makes the car lead toward the side with less.
Toe is whether the fronts of the tires point toward each other (toe-in) or away (toe-out), seen from above. Toe is the biggest tire-wearing angle; wrong toe scuffs the tread into feathered, saw-tooth edges.

Setting alignment takes special equipment and a qualified technician. A car that pulls to one side on a straight, level road may need it, but check the simple thing first: an under-inflated tire can cause a pull too.

Angles exaggerated so you can see them. Source: Southern Illinois University Automotive Technology.

Parts and what they do
Part	What it does	Signs of trouble
Coil springs	Hold the car up and absorb bumps.	Sagging; a technician checks ride height.
Shock absorbers and struts	Damp the bouncing with fluid forced through small holes.	Bouncy ride, poor cornering, oily leaks on the body; leaking struts are replaced in pairs.
Control arms and bushings	Locate the wheel and let it move up and down.	Wandering, clunks, uneven tire wear.
Ball joints	Swivels that let the knuckle move and steer.	A clunking or popping sound when turning or going over bumps.
Sway bar and links	Limit body roll in turns.	Clunks over bumps from loose parts.
Rack and pinion	Turns steering-wheel rotation into side-to-side motion.	Hard steering from binding; red fluid leaks on hydraulic systems.
Tie rods	Push and pull the steering arms; adjust toe.	Wandering, loose steering, feathered tire wear.
Power steering pump or motor	Adds steering assist.	Heavy steering; a squeal from a slipping belt on hydraulic systems.

You canWhat you can safely do

Keep the tires at the recommended pressure; low tires cause hard steering and pulling (Check Tire Pressure and Tread).
Watch your tires for uneven wear, which often points to alignment or worn parts (Lesson 10).
Notice changes: new clunks, a crooked steering wheel when driving straight, or the car drifting.

StopWhen to call a professional

Suspension and steering parts hold the car on the road, and springs store a lot of energy. Replacing them, and setting alignment, are jobs for a technician with the right tools and specifications. Get the car checked promptly if steering suddenly gets loose or heavy, or if you hear a new clunk from the front end.

Check yourself

Tap an answer to check it, or open “Show the answer.”

What does a shock absorber do?
Show the answer
Damps bouncing by forcing fluid through small openings. Springs hold the car up; shocks slow the springs’ motion so the car doesn’t keep bouncing.
Which alignment angle wears tires fastest when it’s wrong?
Show the answer
Toe. Toe is called the biggest tire-wearing angle; it scrubs the tires sideways as they roll.
What helps the steering wheel return to center after a turn?
Show the answer
Positive caster. With the steering axis tilted back, the tire trails behind its pivot like a shopping-cart wheel and pulls itself straight.
A car drifts to the right on a level road. What should you check first?
Show the answer
The tire pressures. Under-inflated tires can cause pulling; check them before paying for an alignment.

Go deeper

Southern Illinois University Automotive Technology: Alignment Information and Vocabulary An automotive program’s guide to every alignment angle.
U.S. Navy, Construction Mechanic Basic (NAVEDTRA 14264A), Chapter 14: Automotive Chassis and Body The Navy’s chapter on frames, suspension, steering, wheels and tires.
Clemson University Vehicular Electronics Laboratory: Electric Power-Assisted Steering How electric power steering works.

Sources

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A free course from Teddy Rook Book. It explains how cars work in general and follows U.S. sources; your owner’s manual and your vehicle’s service information are the final word for your car, along with state and local rules.