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King pin inclination

Motorsport Wheel Alignment Fundamentals

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Discussion and questions related to the course Motorsport Wheel Alignment Fundamentals

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Does adjusting camber on the top of the shock mounts as is common practice with most coil over set ups also change the King pin inclination.

Yes, as you're clearly referring to a MacPherson strut*.

The 'kingpin inclination' is the angle between the axis the stub axle assembly rotates around and the vertical, as seen from the front. With the MacPherson strut the two points that set the angle are the bottom mount, where it is attached to the wishbone/track control arm and the top mount bearing. So moving the top mount will move the KPI by the same degree the camber is changed.

*That is just one type of "coil over" and some are used with double wishbone, or multi-link, suspension designs with different top mount positions available.

If so, then why is it not likely to be adjustable and only when we get to professional level motorsport where adjusting it is possible? Just curious if there is more to it

Hairul, I'm not sure if I understand your question. If you have an adjustable top plate for camber (I pasted an image below) which is common in most aftermarket coilover kits for a MacPherson strut, when you adjust camber, you are also adjusting the KPI.

Tim, I'm referring to what is said in the KPI module: "KPI is an aspect of production cars that's likely not adjustable and only when we get to professional level motorsport we may have the option of changing it."

As you said, adjustable strut tops are common so I'm wondering why in the course it is mentioned as unlikely to be adjustable. Also for the fact that nothing is said in the course about how adjusting camber with strut tops result in KPI change (or have I missed it?), hence my curiosity that there is something I don't quite understand.

Hairul, I think the point being made in the module you refer to is that for an unmodified factory road car the KPI is very unlikely to be adjustable. It's only when you start fitting aftermarket parts that you will get some adjustability in most cases.

I've added a small diagram below to be clear on how KPI and camber are related, but I think you understand already.

The thing I think might be confusing you is that camber is often adjustable but KPI isn't? In the case of a MacPherson strut, you can often have slotted holes in the upright attachment to the strut as shown below. You can see if you adjust the camber in this way, the KPI would not change, although the scrub radius would!

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