Xem Studiomeasured geometry

Library › Car design › Suspension geometry ·

Kingpin inclination (KPI / SAI)

What is kingpin inclination and what does it do? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: kingpin inclination, KPI, steering axis inclination, SAI, king pin angle, kpi vs caster, kingpin axis, steering axis tilt, rc kingpin, included angle

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

sizes
2 in table

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.

Kingpin inclination size chart

parametervalue or rangesource
FSAE example KPI-2.353 deg front, -2.249 deg rear (team sign convention)Univ. of Utah FSAE
Adjustabilityusually fixed on production carsHPA

Where the files are

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

High Performance AcademyWheel alignment terminology: king pin inclination and scrub radiuswebPublisher's page; dimensions are facts
Suspension SecretsSuspension geometry explainedwebPublisher's page; dimensions are facts
WikipediaScrub radiuswebPublisher's page; dimensions are facts
University of Utah, Mechanical EngineeringFormula SAE Suspension System (senior design)webPublisher'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

kingpin-inclination-geometrykpi demo: front axle, track 190 mm, Ø50 tyres, 2.35° (illustrative layout)STEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
Set it up →

Plain text: sheet.txt · JSON: /api/geometry?object=kingpin-inclination

Kingpin inclination (KPI / SAI), isometric render of a generated part
Render of kingpin-inclination-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
Ackermann steering geometry, isometric render of a generated part
Ackermann steering geometry4 sizes★ 1 file

Questions

Is KPI adjustable?

Usually not on production cars; HPA says only at professional motorsport level.