# Kingpin inclination (KPI / SAI)

> What is kingpin inclination and what does it do?

- Category: Car design › Suspension geometry
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/kingpin-inclination/ · JSON: https://xemstudio.com/api/geometry?object=kingpin-inclination · Plain text: https://xemstudio.com/objects/kingpin-inclination/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

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

## 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.

## Sizes

| 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 |

## Where the files are

- High Performance Academy: [Wheel alignment terminology: king pin inclination and scrub radius](https://www.hpacademy.com/courses/motorsport-wheel-alignment-fundamentals/wheel-alignment-terminology-king-pin-inclination-and-scrub-radius) — web — Publisher's page; dimensions are facts
- Suspension Secrets: [Suspension geometry explained](https://suspensionsecrets.co.uk/suspension-geometry-explained) — web — Publisher's page; dimensions are facts
- Wikipedia: [Scrub radius](https://en.wikipedia.org/wiki/Scrub_radius) — web — Publisher's page; dimensions are facts
- University of Utah, Mechanical Engineering: [Formula SAE Suspension System (senior design)](https://mech.utah.edu/wp-content/uploads/2024/12/5-Formula-SAE-Suspension.pdf) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/kingpin-inclination/index.json · license: https://xemstudio.com/files/hardware/kingpin-inclination/LICENSE.md

- kingpin-inclination-geometry: [STEP](https://xemstudio.com/files/hardware/kingpin-inclination/kingpin-inclination-geometry.step) · [STL](https://xemstudio.com/files/hardware/kingpin-inclination/kingpin-inclination-geometry.stl) — kpi demo: front axle, track 190 mm, Ø50 tyres, 2.35° (illustrative layout)

## Questions

**Is KPI adjustable?**

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

## Fits with

- [Camber angle](https://xemstudio.com/objects/camber/)
- [Caster angle](https://xemstudio.com/objects/caster/)
- [Front kick-up (RC)](https://xemstudio.com/objects/kick-up/)
- [Front toe (toe-in / toe-out)](https://xemstudio.com/objects/toe-front/)
- [Rear toe-in](https://xemstudio.com/objects/toe-rear/)
- [Ackermann steering geometry](https://xemstudio.com/objects/ackermann/)