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Ackermann steering geometry

What is Ackermann steering and how is it calculated? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: ackermann, ackerman steering, ackermann geometry, ackermann angle, rc ackermann, steering geometry inner wheel, ackermann formula, 100% ackermann, ackermann plate, steering trapezoid

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

sizes
4 in table

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.

Ackermann steering geometry size chart

parametervalue or rangesource
Ackermann conditioncot(phi_o) - cot(phi_i) = w / lraw.org
Inner wheel anglephi_i = atan(2l sin phi / (2l cos phi - w sin phi))raw.org
Steering-arm rulearm pivots on line from kingpin to rear-axle centreWikipedia
InventedLankensperger 1816; Ackermann patent 1818Wikipedia

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

raw.org (kinematics notes)Ackerman steeringwebPublisher's page; dimensions are facts
WikipediaAckermann steering geometrywebPublisher's page; dimensions are facts
CompetitionXRC Ackermann Steering ExplainedwebPublisher's page; dimensions are facts
Tekno RCTekno RC Setup GuidewebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

ackermann-geometryAckermann demo: inner wheel 30°, outer wheel per the Ackermann relation for wheelbase 260, track 190 (illustrative layout)STEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=ackermann

Ackermann steering geometry, isometric render of a generated part
Render of ackermann-geometry from the free STEP; not to scale.

Fits with

Camber angle, isometric render of a generated part
Camber angle4 sizes★ 1 file
Caster angle, isometric render of a generated part
Caster angle5 sizes★ 1 file
Front kick-up (RC), isometric render of a generated part
Front kick-up (RC)4 sizes★ 1 file
Front toe (toe-in / toe-out), isometric render of a generated part
Front toe (toe-in / toe-out)3 sizes★ 1 file
Rear toe-in, isometric render of a generated part
Rear toe-in3 sizes★ 1 file
Reverse (anti-) Ackermann, isometric render of a generated part
Reverse (anti-) Ackermann2 sizes★ 1 file

Questions

Does Ackermann depend on wheelbase?

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