# Ackermann steering geometry

> What is Ackermann steering and how is it calculated?

- Category: Car design › Suspension geometry
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/ackermann/ · JSON: https://xemstudio.com/api/geometry?object=ackermann · Plain text: https://xemstudio.com/objects/ackermann/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Ackermann geometry turns the inside wheel more than the outside so both roll around one common centre without scrubbing (Wikipedia). The ideal condition is cot(outer) - cot(inner) = track / wheelbase (raw.org).
- A simple layout points the steering arms toward the centre of the rear axle so the tie rod and axle form a trapezium (Wikipedia).
- On RC cars more Ackermann gives sharper turn-in but can feel twitchy at speed and wears the inside front tyre (CompetitionX); Tekno adjusts it by moving the steering link fore or aft.
- The file is a reference example built by Xem Studio from the numbers above (Reference 1/10 touring car: wheelbase 260 mm (AARCMCC ISTC 250-270), track 190 mm (EFRA width without body), 50 mm = EFRA rim limit.). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

## Sizes

| parameter | value or range | source |
|---|---|---|
| Ackermann condition | cot(phi_o) - cot(phi_i) = w / l | raw.org |
| Inner wheel angle | phi_i = atan(2l sin phi / (2l cos phi - w sin phi)) | raw.org |
| Steering-arm rule | arm pivots on line from kingpin to rear-axle centre | Wikipedia |
| Invented | Lankensperger 1816; Ackermann patent 1818 | Wikipedia |

## Where the files are

- raw.org (kinematics notes): [Ackerman steering](https://raw.org/book/kinematics/ackerman-steering/) — web — Publisher's page; dimensions are facts
- Wikipedia: [Ackermann steering geometry](https://en.wikipedia.org/wiki/Ackermann_steering_geometry) — web — Publisher's page; dimensions are facts
- CompetitionX: [RC Ackermann Steering Explained](https://www.competitionx.com/?p=14) — web — Publisher's page; dimensions are facts
- Tekno RC: [Tekno RC Setup Guide](https://teknoforums.com/misc/Tekno-RC-Setup-Guide.pdf) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/ackermann/index.json · license: https://xemstudio.com/files/hardware/ackermann/LICENSE.md

- ackermann-geometry: [STEP](https://xemstudio.com/files/hardware/ackermann/ackermann-geometry.step) · [STL](https://xemstudio.com/files/hardware/ackermann/ackermann-geometry.stl) — Ackermann demo: inner wheel 30°, outer wheel per the Ackermann relation for wheelbase 260, track 190 (illustrative layout)

## Questions

**Does Ackermann depend on wheelbase?**

Yes; the ideal difference between wheel angles grows with track/wheelbase (raw.org).

## Fits with

- [Camber angle](https://xemstudio.com/objects/camber/)
- [Caster angle](https://xemstudio.com/objects/caster/)
- [Front kick-up (RC)](https://xemstudio.com/objects/kick-up/)
- [Front toe (toe-in / toe-out)](https://xemstudio.com/objects/toe-front/)
- [Rear toe-in](https://xemstudio.com/objects/toe-rear/)
- [Reverse (anti-) Ackermann](https://xemstudio.com/objects/anti-ackermann/)