An Ackermann steering mechanism allows the inner wheel to turn at a sharper angle than the outer wheel during a turn, so both front wheels trace arcs around the same center point. Building one requires getting the geometry right first, then fabricating a simple trapezoid-shaped linkage that produces the correct angle difference. Whether you’re building a go-kart, a small EV, a soap box racer, or a robotics project, the core process is the same.
How Ackermann Geometry Works
When a vehicle turns, the inner front wheel needs to steer at a greater angle than the outer wheel because it follows a tighter arc. If both wheels turned the same amount, the tires would fight each other, scrubbing sideways across the pavement. This wastes energy, destroys tires, and makes the vehicle handle poorly.
The Ackermann principle solves this by angling the steering arms inward so that imaginary lines drawn through both steering arms meet at the center of the rear axle. This creates a trapezoid-shaped linkage (not a perfect rectangle), and that trapezoid naturally produces a greater turning angle on the inside wheel. The relationship between the two wheel angles is governed by one core equation:
cot(outer angle) minus cot(inner angle) = track width / wheelbase
Track width is the distance between your two front wheel centers. Wheelbase is the distance from the front axle to the rear axle. These two measurements are the foundation of everything that follows.
Calculating Your Steering Angles
Before cutting any metal, you need to calculate the ideal inner and outer wheel angles for your vehicle’s dimensions. Start by measuring your wheelbase and track width in the same units.
For any given steering input, the left and right wheel angles are:
- Inner wheel angle = arctan(wheelbase × tan(steering angle) / (wheelbase + 0.5 × track width × tan(steering angle)))
- Outer wheel angle = arctan(wheelbase × tan(steering angle) / (wheelbase − 0.5 × track width × tan(steering angle)))
For example, if your wheelbase is 40 inches and your track width is 30 inches, plug those values in for several steering angles (10°, 20°, 30°) to see how the inner and outer angles diverge. At small angles the difference is slight. At full lock, the inner wheel might be at 35° while the outer is only at 25°. Building a spreadsheet or using an online Ackermann calculator saves time here and lets you check your linkage design against the ideal numbers.
Designing the Trapezoid Linkage
The physical mechanism is a four-bar linkage shaped like a trapezoid. It has four key parts: two steering arms (one on each wheel’s knuckle), one tie rod connecting them, and the front axle or frame rail acting as the fixed base. The steering arms are shorter than the tie rod, and they angle inward, which is what creates the trapezoid shape and produces the Ackermann effect.
Setting the Steering Arm Angle
The classic rule of thumb is to angle each steering arm so that a line drawn along the arm, from the kingpin (steering pivot) to the tie rod end, points directly at the center of the rear axle. This gives you approximately 100% Ackermann geometry. You can verify this by laying your chassis on a flat surface, marking the rear axle centerpoint, and using a string line from that point through each kingpin. The tie rod mounting hole on each steering arm should fall on or near that string line.
If the steering arms point straight ahead (parallel to the chassis), you get zero Ackermann, meaning both wheels turn the same amount. If they angle inward past the rear axle center, you get more than 100%. For most street and low-speed applications, 100% or close to it is the target. Some racing applications deliberately use less Ackermann, but for a DIY build, starting at 100% gives you clean, predictable handling.
Choosing Steering Arm Length
The length of your steering arms controls how much the wheels turn for a given amount of tie rod movement. Shorter arms give more turning angle per unit of tie rod travel, but they also require more force. For a go-kart or small vehicle, steering arms between 3 and 6 inches are typical. Make both arms the same length unless you have a specific reason not to.
Sizing the Tie Rod
The tie rod connects the outer ends of both steering arms. Its length equals the distance between the two tie rod mounting points when the wheels are pointed straight ahead. Measure this carefully after your steering arms are positioned. The tie rod needs to be adjustable in length so you can fine-tune toe alignment later. Threading rod ends onto each end of a steel tube gives you that adjustability.
Materials and Hardware
For the tie rod itself, mild steel tubing works for low-speed projects like go-karts. For anything faster or heavier, use chromoly steel tubing (4130 is the standard choice for racing fabrication). Wall thickness of 0.120 inches is a common starting point for small vehicles. For full-size off-road builds, 7/8-inch or 3/4-inch diameter chromoly tubing with appropriate wall thickness handles the loads.
Rod ends (also called heim joints) are the pivoting connectors at each end of the tie rod. They thread into the tube and allow the linkage to articulate as the wheels turn. For a go-kart or lightweight build, 3/8-inch or 1/2-inch rod ends are sufficient. Heavier vehicles typically use 3/4-inch or 7/8-inch heim joints. Use a right-hand thread on one end and a left-hand thread on the other so you can adjust the tie rod length by simply rotating the tube without disconnecting either end.
Steering knuckles can be fabricated from 1/4-inch or 3/8-inch steel plate, depending on vehicle weight. The knuckle needs a kingpin bore (or bolt hole for the steering pivot), a spindle or hub mounting point for the wheel, and a drilled hole for the tie rod end. If you’re building from scratch, cut the knuckles from plate steel and drill the tie rod hole at the angle you calculated for your Ackermann geometry.
Step-by-Step Assembly
Start with your frame or front axle mounted and your wheelbase and track width finalized. Any changes to those dimensions after you build the linkage will throw off your geometry.
Mount your kingpins or steering pivots on both sides. These are the vertical axes each front wheel rotates around when you steer. On a simple go-kart, a bolt through the frame with bushings can serve as the kingpin. On a more serious build, use actual kingpin assemblies or ball joints.
Attach your steering knuckles to the kingpins and mount the wheels. With the wheels pointing straight ahead, confirm your track width measurement. Then install your steering arms onto the knuckles, with the tie rod mounting holes angled inward toward the rear axle center as described above. If your knuckles and steering arms are one piece, this angle is already built in when you fabricate them.
Thread your rod ends onto each end of the tie rod tube and connect them to the steering arm holes. Adjust the tie rod length until both wheels point straight ahead with equal toe (ideally a slight toe-in of about 1/16 inch total for stability). Lock the rod end jam nuts once alignment is set.
Finally, connect your steering input. This can be a steering wheel with a shaft going to a pitman arm that pushes or pulls the tie rod, or a rack and pinion unit, or even a simple lever on one knuckle. The key is that the steering input moves the tie rod side to side, which turns both wheels through the trapezoid linkage.
Testing and Adjusting
With the vehicle on a flat surface, turn the wheels to full lock in both directions. Measure the inner and outer wheel angles with a protractor or angle finder and compare them to your calculated ideal values. They won’t match perfectly because a four-bar linkage only approximates true Ackermann geometry, but they should be close.
If the difference between inner and outer angles is too small (both wheels turning nearly the same amount), your steering arms aren’t angled inward enough. If the difference is too large, they’re angled inward too much. Adjusting means either refabricating the steering arms or, if you designed them with multiple mounting holes, moving the tie rod attachment point.
On a test drive, watch for signs of poor geometry. Uneven front tire wear, especially feathering or scrubbing on the edges, means the wheels are fighting each other through turns. The vehicle pulling to one side during turns or requiring excessive effort to steer at low speed also suggests the angles are off. A correctly set up Ackermann linkage makes the vehicle feel light and natural through corners, with the tires rolling cleanly instead of sliding.
Common Mistakes to Avoid
The most frequent error is making the steering arms parallel to the chassis centerline instead of angling them inward. This produces zero Ackermann and guarantees tire scrub in every turn. The second most common mistake is making the two steering arms different lengths or mounting them at different angles, which gives you asymmetric steering: the vehicle turns tighter one direction than the other.
Another pitfall is ignoring bump steer. If the tie rod isn’t at the same height and angle as your suspension’s control arms (or axle pivot), the wheels will toe in or out as the suspension moves over bumps. On a solid-axle or no-suspension build like a basic go-kart, this isn’t a concern. On anything with independent front suspension, the tie rod inner mounting points need to be at the same height as the lower control arm pivot points.
Finally, make sure your rod ends and tie rod tube are strong enough for your application. Undersized hardware on a heavier vehicle can bend or break under hard cornering loads. When in doubt, go one size up on rod ends and one step up in tubing wall thickness.