Glossary
Ackermann Steering Explained: Geometry, Percentages & Handling
Ackermann steering geometry describes how much more the inside front wheel turns than the outside wheel as the steering is applied. With 100% Ackermann both wheels point at the same turn centre, which suits low-speed, low-slip cornering; with parallel steering both turn equally; anti-Ackermann turns the outside wheel more. Race cars choose the amount based on tyre slip angle behaviour and how much the inside front is loaded.
| Setting | Inside vs outside steer | Typical use |
|---|---|---|
| 100% (full) Ackermann | Inside steers significantly more | Karts, speedway, tight street circuits |
| 30–60% Ackermann | Inside steers slightly more | Most touring and GT cars |
| Parallel (0%) | Equal | Fast circuits, balanced slip angles |
| Anti-Ackermann | Outside steers more | Formula cars with heavy aero load on the outside tyre |
Why it matters
The lightly loaded inside front tyre reaches its peak grip at a smaller slip angle than the heavily loaded outside tyre. If both wheels steer equally, one of them is always working away from its optimum. Positive Ackermann helps in slow corners where the geometry dominates; in fast corners the outside tyre needs more slip angle, which is why fast cars tend towards parallel or anti-Ackermann.
Adjusting Ackermann
Moving the outer tie rod end forward or back on the upright changes the steering arm angle and therefore the Ackermann percentage. Moving the rack fore and aft has a similar effect. Any change alters bump steer and toe, so re-check both. On karts, Ackermann is built into the stub axles and tuned with different spindle offsets.
Frequently asked questions
Does more Ackermann reduce understeer?
In slow corners it often does, because the inside front stops scrubbing and contributes grip. In fast corners excess Ackermann can overheat the inside front and add understeer instead.
How do I measure Ackermann?
On turn plates, apply a fixed steering angle (say 20° on the outside wheel) and read the inside wheel. The difference, compared with the geometric ideal for the wheelbase and track, gives the percentage.
Why do speedway cars run so much Ackermann?
They run large steering angles in slow, sliding corners where the inside front is very lightly loaded. Full Ackermann stops that tyre from dragging and helps the car turn.
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