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KPI and camber gain

Motorsport Wheel Alignment Fundamentals

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Discussion and questions related to the course Motorsport Wheel Alignment Fundamentals

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I had a hard time visualizing how increased KPI angle will result in more positive camber to the outside wheels when turning. Easy to understand how positive caster promotes negative camber gain though.

I watched a youtube video explaining things and they really proved that KPI will reduce the negative camber to the outside wheel during cornering, but how? Is there anywhere on internet I can see this effect in action?

Hello Hairul,

Adding KPI does indeed decrease negative camber on the outside front wheel. I don't have a good internet source for helping you visualise this, but if you look at a suspension form front on that has positive KPI then you can imagine the whole assembly rotating down (you add a vertical component to the wheel travel when you add positive KPI). In this case, it seems pretty clear to me that you will add positive camber to the outside tyre. Maybe we need to add an animation into the course to help make it clearer.

Tim

Tim is correct. Adding positive caster will reduce camber on turn-in, if that's what is confusing you?

Yes. Animation will be great.

This is how I imagine camber gain works for positive caster. I've drawn it out in the attached pictures.

The first pic I show caster by looking at the side. The wheel have 0° of camber. Now when we turn the wheel, it will move on the caster axis. The shock is at an angle so if we plot a line along its rotation, we can see that it will not move flat. Instead, it will have high spot and low spot and everything in between. In the right, I've drawn the wheel in full lock (exagerated) and we can see the wheel ended in the high spot and now it suddenly have extreme camber, matching the caster angle. This is the outside wheel in a right hand corner. Because the wheel is now in high spot, the wheel actually lift a little bit from the ground, while the inside wheel will drop and lift the car up.

In the second pic, I draw a front view drawing of wheel with zero camber and excessive KPI. If we turn to full lock and look at it from the side, there's no camber losed. It starts with 0 and stays 0 at full lock. Even if you set it with neg camber and then turn to full lock, it'll still be 0°. No matter how much your KPI or how much camber you set

Attached Files

Uh, seems like you're forgetting the relationship between the axis of the wheel and the axis of caster, and KPI, the stub axle is being rotated about are fixed in relationship to each other, in three dimensions - your sketches certainly don't seem show that, but that may be down to the quality of them ;-).

Sorry I don't understand. If you can dumb that down for me or direct me to a visual aid I would be truly grateful for that. It's been months of struggle to wrap this concept round my head

Hairul, I wonder if a physical model might be helpful for you. Maybe something with some cardboard and a toothpick? I certainly find playing with something physical helps me grasp things sometimes!

That last sentence could be taken out of context so easily Tim!

OK, consider the camber of the wheel, as seen from in front, and the KPI which is the axis the wheel assembly will rotate around, then the angle between those two - this angle is fixed because it's built into the whole assembly.

Now consider the caster as seen from the side, this is the same axis as the KPI, just seen from the side.

Now consider what happens if the wheel is turned to 90 degrees - that angle between the KPI and the camber is now the angle between the camber and the caster axis - same axis, remember - you will see there is quite a lot of positive* camber now at the wheel, and different whether turned to the front or to the rear. As the wheel assemble was rotated it was progressively gained.

*Remember, positive camber is when the top of the wheel is leaning out, negative when leaning in.

Maybe I need to re-read my posts before sending them, Stephen!

Thanks for the explanation, Gord. I've got to say though, even I struggle a little to translate all that to something physical in my head.

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