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Caster angle

What is caster and why do race cars and RC cars run so much of it? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: caster, castor, rc caster block, caster trail, mechanical trail, positive caster, caster self centering, c-hub caster, how much caster, caster vs camber

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

sizes
5 in table

Notes

  • Caster is the side-view tilt of the steering axis. With positive caster the axis meets the road ahead of the contact patch, so the wheel trails and self-centres, improving directional stability (Wikipedia).
  • More caster gives straight-line stability and camber gain when steering but heavier, less responsive steering (Wikipedia; Formula1-Dictionary). On RC cars, higher caster gives more stability and less off-power corner-entry steering (Tekno).
  • Road cars commonly run over 7 deg with radial tyres; some F1 cars exceed 10 deg; RC buggies stack kick-up and caster-block angles to well over 20 deg.
  • The file is a reference example built by Xem Studio from the numbers above (Reference 1/10 off-road: track 250 mm and 90 mm wheel+tyre (EFRA maxima); wheelbase illustrative.). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

Caster angle size chart

parametervalue or rangesource
Road cars (radial tyres)over 7 deg commonWikipedia
F1at least a few deg; some over 10 degFormula1-Dictionary
FSAE example+2.923 deg front, mechanical trail 11.667 mmUniv. of Utah FSAE
RC total caster example11 deg kick-up + 0.5 deg insert + 15 deg block = 26.5 degTekno setup guide
RC caster blocks (C-hub)21, 18, 15 deg optionsAdrenaline RC

Where the files are

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

WikipediaCaster anglewebPublisher's page; dimensions are facts
Formula1-DictionaryCastor anglewebPublisher's page; dimensions are facts
University of Utah, Mechanical EngineeringFormula SAE Suspension System (senior design)webPublisher's page; dimensions are facts
Tekno RCTekno RC Setup GuidewebPublisher's page; dimensions are facts
Adrenaline RC RacingMastering Caster & Kick-Up for Better Offroad RC Racing PerformancewebPublisher'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

caster-geometryCaster demo: steering axis tilted back 26.5°, wheelbase 260 mm, Ø90 tyres (illustrative layout)STEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=caster

Caster angle, isometric render of a generated part
Render of caster-geometry from the free STEP; not to scale.

Fits with

Camber angle, isometric render of a generated part
Camber angle4 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
Ackermann steering geometry, isometric render of a generated part
Ackermann steering geometry4 sizes★ 1 file
Reverse (anti-) Ackermann, isometric render of a generated part
Reverse (anti-) Ackermann2 sizes★ 1 file

Questions

Why does caster add camber when steering?

Tilting the steering axis back makes the outside wheel lean in as it steers; racers use large caster for this camber gain (Wikipedia).