{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "kingpin-inclination",
 "name": "Kingpin inclination (KPI / SAI)",
 "kind": "standard",
 "category": "Car design",
 "group": "Suspension geometry",
 "year": null,
 "question": "What is kingpin inclination and what does it do?",
 "tags": [
  "vehicle design",
  "suspension geometry",
  "rc design",
  "aerodynamics"
 ],
 "aliases": [
  "kingpin inclination",
  "KPI",
  "steering axis inclination",
  "SAI",
  "king pin angle",
  "kpi vs caster",
  "kingpin axis",
  "steering axis tilt",
  "rc kingpin",
  "included angle"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/kingpin-inclination/",
 "sheet_txt": "https://xemstudio.com/objects/kingpin-inclination/sheet.txt",
 "sheet": {
  "basis": "Design rules and figures from the cited sources; example geometry by Xem Studio",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "KPI is the front-view tilt of the steering axis through the upper and lower ball joints (HPA). As the wheel steers, KPI lifts the car, so the steering wants to return to centre; too much makes steering very heavy.",
   "KPI pushes the wheel toward positive camber when steering, partly cancelling caster's camber gain (HPA), and together with wheel offset it sets the scrub radius (Suspension Secrets).",
   "Inclining the axis inward means less positive caster is needed for directional stability (Wikipedia, Scrub radius).",
   "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."
  ],
  "table": {
   "columns": [
    "parameter",
    "value or range",
    "source"
   ],
   "rows": [
    [
     "FSAE example KPI",
     "-2.353 deg front, -2.249 deg rear (team sign convention)",
     "Univ. of Utah FSAE"
    ],
    [
     "Adjustability",
     "usually fixed on production cars",
     "HPA"
    ]
   ]
  }
 },
 "sheet_text": "Kingpin inclination (KPI / SAI) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/kingpin-inclination/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Design rules and figures from the cited sources; example geometry by Xem Studio\nCatalog version: 2026-10-20\n\nSizes: see table below\n- KPI is the front-view tilt of the steering axis through the upper and lower ball joints (HPA). As the wheel steers, KPI lifts the car, so the steering wants to return to centre; too much makes steering very heavy.\n- KPI pushes the wheel toward positive camber when steering, partly cancelling caster's camber gain (HPA), and together with wheel offset it sets the scrub radius (Suspension Secrets).\n- Inclining the axis inward means less positive caster is needed for directional stability (Wikipedia, Scrub radius).\n- 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.\n\nparameter  value or range  source\nFSAE example KPI  -2.353 deg front, -2.249 deg rear (team sign convention)  Univ. of Utah FSAE\nAdjustability  usually fixed on production cars  HPA\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- High Performance Academy: Wheel alignment terminology: king pin inclination and scrub radius — web — Publisher's page; dimensions are facts — https://www.hpacademy.com/courses/motorsport-wheel-alignment-fundamentals/wheel-alignment-terminology-king-pin-inclination-and-scrub-radius\n- Suspension Secrets: Suspension geometry explained — web — Publisher's page; dimensions are facts — https://suspensionsecrets.co.uk/suspension-geometry-explained\n- Wikipedia: Scrub radius — web — Publisher's page; dimensions are facts — https://en.wikipedia.org/wiki/Scrub_radius\n- University of Utah, Mechanical Engineering: Formula SAE Suspension System (senior design) — web — Publisher's page; dimensions are facts — https://mech.utah.edu/wp-content/uploads/2024/12/5-Formula-SAE-Suspension.pdf\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/kingpin-inclination/index.json\nAPI: https://xemstudio.com/api/geometry?object=kingpin-inclination\n",
 "sources": [
  {
   "publisher": "High Performance Academy",
   "title": "Wheel alignment terminology: king pin inclination and scrub radius",
   "url": "https://www.hpacademy.com/courses/motorsport-wheel-alignment-fundamentals/wheel-alignment-terminology-king-pin-inclination-and-scrub-radius",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Suspension Secrets",
   "title": "Suspension geometry explained",
   "url": "https://suspensionsecrets.co.uk/suspension-geometry-explained",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Scrub radius",
   "url": "https://en.wikipedia.org/wiki/Scrub_radius",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "University of Utah, Mechanical Engineering",
   "title": "Formula SAE Suspension System (senior design)",
   "url": "https://mech.utah.edu/wp-content/uploads/2024/12/5-Formula-SAE-Suspension.pdf",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "camber",
  "caster",
  "kick-up",
  "toe-front",
  "toe-rear",
  "ackermann"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [],
 "faq": [
  {
   "q": "Is KPI adjustable?",
   "a": "Usually not on production cars; HPA says only at professional motorsport level."
  }
 ],
 "files_license": {
  "name": "Xem Studio Design License",
  "holder": "Xem Studio",
  "url": "https://xemstudio.com/license/",
  "note": "Xem Studio's own design: free to use, print, modify and sell things made from it; not to be republished or redistributed as files."
 },
 "offers": [
  {
   "file": "kingpin-inclination-geometry",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/kingpin-inclination/kingpin-inclination-geometry.step",
   "stl": "https://xemstudio.com/files/hardware/kingpin-inclination/kingpin-inclination-geometry.stl",
   "note": "kpi demo: front axle, track 190 mm, Ø50 tyres, 2.35° (illustrative layout)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/kingpin-inclination/index.md"
}