Kingpin inclination (KPI / SAI) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/kingpin-inclination/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
Catalog version: 2026-10-20

Sizes: see table below
- 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.

parameter  value or range  source
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

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- 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
- Suspension Secrets: Suspension geometry explained — web — Publisher's page; dimensions are facts — https://suspensionsecrets.co.uk/suspension-geometry-explained
- Wikipedia: Scrub radius — web — Publisher's page; dimensions are facts — https://en.wikipedia.org/wiki/Scrub_radius
- 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

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/kingpin-inclination/index.json
API: https://xemstudio.com/api/geometry?object=kingpin-inclination