How To Make An Ackermann Steering Mechanism?

Building an Ackermann steering mechanism is a precise woodworking and metalworking project that requires careful geometry. The core principle is that when you turn the steering wheel, the inner wheel turns at a sharper angle than the outer wheel. This difference prevents tire scrubbing and keeps all four wheels rolling on concentric circles during a turn. To achieve this, you must position the steering arms so that lines drawn from each kingpin through the steering arm ball joint intersect at the center of the rear axle when the wheels are pointing straight ahead.

What Is the Ackermann Steering Geometry?

The Ackermann principle is named after Rudolph Ackermann, who patented the design in 1818. The mechanism solves a real physics problem. When a car turns, the inner wheel travels a shorter path than the outer wheel. If both front wheels turned at the same angle, the tires would fight each other and scrub sideways against the road.

The solution is simple geometry. The steering arms are angled inward, not parallel to the axle. When you draw an imaginary line through each steering arm pivot point and extend it toward the rear of the vehicle, both lines should meet at the center point of the rear axle. This single intersection point is what creates the correct angle difference between the inner and outer wheels during a turn.

This geometry is not just for race cars. Every passenger vehicle on the road uses some form of Ackermann steering. It reduces tire wear, improves stability, and makes the car feel predictable when cornering.

What Tools and Materials Do You Need?

Before you start cutting metal or wood, gather the right equipment. The exact materials depend on whether you are building a full-size vehicle, a go-kart, or a model. The geometry is identical regardless of scale.

• Steering arms: Steel plate or bar stock, typically 6-10 mm thick for small vehicles
• Tie rods: Threaded rod with rod ends or ball joints on each end
• Spindles or uprights: The components that hold the wheel hubs and pivot on the kingpins
• Kingpins: The vertical pivot points for each front wheel
• Pitman arm or steering arm: The lever that connects the steering column to the tie rod
• Welder: MIG or TIG for steel, or a strong epoxy if building a wooden model
• Angle grinder: For cutting and shaping metal
• Drill press: For accurate hole placement
• Measuring tools: Tape measure, protractor, and a laser level or string line for alignment

For a wooden educational model, you can use plywood, dowel rods, and screws. The principles remain exactly the same. For a go-kart or a functioning vehicle, use steel and proper welding techniques.

How Do You Calculate the Correct Steering Arm Angle?

The steering arm angle is the single most important measurement in the entire build. Get this wrong and the mechanism will not work correctly.

Start by measuring the distance between the two kingpin centers. This is your track width at the kingpins. Then measure the wheelbase, which is the distance from the front axle centerline to the rear axle centerline.

Now draw a line from the center of the rear axle to the center of one front kingpin. The angle between this line and the front axle is your steering arm angle. Both steering arms must be angled inward at exactly this same angle.

For example, if your wheelbase is 60 inches and your kingpin center distance is 40 inches, the steering arm angle works out to roughly 18 degrees. You can calculate this using trigonometry: the angle is the arctangent of (half the kingpin distance divided by the wheelbase). In this case, arctan(20/60) gives you about 18.4 degrees.

This angle is not a guess. It is a direct mathematical consequence of your vehicle’s dimensions. If you change the wheelbase or the track width, the angle changes too.

How Do You Assemble the Mechanism Step by Step?

Start with the steering arms. Cut two identical arms from steel plate. Drill a hole at one end for the kingpin and another hole at the opposite end for the tie rod ball joint. The angle between the centerline of the arm and the tie rod hole must match the angle you calculated.

Attach the steering arms to the spindles. Weld or bolt them so they point inward toward the center of the vehicle. The tie rod holes should be closer to the center line than the kingpin holes.

Install the kingpins. These must be perfectly vertical when viewed from the front and perfectly aligned with each other across the vehicle. Use a level to check vertical alignment and a tape measure to confirm equal distance from the chassis centerline.

Connect the tie rod between the two steering arm ball joints. The tie rod should be parallel to the front axle when the wheels point straight ahead. Use left-hand and right-hand threaded rod ends so you can adjust the length and set the toe angle later.

Mount the steering column and pitman arm. The pitman arm connects to one side of the tie rod, usually the driver’s side. When you turn the steering wheel, the pitman arm pushes or pulls the tie rod, which rotates both steering arms and turns both wheels.

Finally, check the full range of motion. Turn the steering wheel from lock to lock. The tie rod ends should not bind or hit the chassis. The ball joints should move freely through the entire range.

How Do You Test and Adjust the Ackermann Effect?

Testing is where most builds succeed or fail. You cannot just assume the geometry is correct because you measured carefully. You must verify it physically.

Place the vehicle on a flat, level surface. Jack up the front end so the wheels are off the ground. Mark the center of the rear axle on the floor with chalk or tape. Then mark the center of each front wheel.

Turn the steering wheel fully to one side. Measure the angle of the inner wheel and the outer wheel relative to the straight-ahead position. The inner wheel must turn more than the outer wheel. For a typical 90-degree steering lock at the inner wheel, the outer wheel should be somewhere around 65 to 70 degrees, depending on your exact geometry.

If both wheels turn at the same angle, your steering arms are parallel instead of angled. You need to increase the inward angle of the arms. If the outer wheel turns more than the inner wheel, you have reverse Ackermann, which is wrong for normal road use. Reduce the steering arm angle.

Also check the toe setting. With the wheels pointing straight ahead, the front edges of the tires should be slightly closer together than the rear edges. A small amount of toe-in, typically 1-3 millimeters total, helps straight-line stability.

What Common Mistakes Ruin the Geometry?

The most common mistake is making the steering arms parallel to the axle. This is visually simple but mechanically wrong. Parallel arms produce equal wheel angles, which causes tire scrub and poor handling.

Another frequent error is measuring the steering arm angle from the wrong reference points. The angle must be calculated from the kingpin centers, not from the wheel centers or the tire edges. Tires have width, and measuring from the outside edge introduces error.

Flexible components also ruin the geometry. If you use thin tie rods or weak ball joints, the mechanism flexes under load. The angles change when the vehicle is actually driving. Use components rated for the weight of your vehicle and the forces involved in cornering.

Finally, do not forget the steering stops. These are physical stops that limit how far the wheels can turn. Without them, the tie rod ends can overextend and pop out of their sockets at full lock. Install adjustable stops on the spindles or the chassis.

When Should You Use a Different Steering Geometry?

Ackermann geometry is not the only option. Some race cars use parallel steering or reverse Ackermann. This is intentional and based on tire physics at high speeds.

At low speeds, the Ackermann effect is ideal. Tires roll without scrubbing and parking is easy. At high speeds and high lateral acceleration, the situation changes. The outer tire carries more load and generates more grip when it has a slightly different slip angle. Some race cars deliberately reduce the Ackermann effect or reverse it entirely.

For a road car, a go-kart, or any vehicle that operates below racing speeds, use full Ackermann geometry. The benefits are reduced tire wear, predictable handling, and easier low-speed maneuvering. If you are building a serious track car, you might experiment with reduced Ackermann, but that is a tuning decision based on specific tire data and lap times.