Try this .
KPI greatly affects the amount/timing of camber gain/loss that a spindle can create. It's a little hard to explain without diagrams or mock ups but let me give it a try. Think about this...
If you had a 0* KPI setup with had 0* camber and 0* caster on that spindle. Now you turn that spindle 90* to the rear and now you checked the camber. You would have 0* camber. No camber gain at all with a 0* KPI. Now...
If you had a 13* KPI setup and with 0* camber and 0* caster on that spindle. Now you turn that spindle 90* to the rear and now you check the camber. You would have 13* camber. That's 13* camber gain with a 13* KPI.
You would have the same results with a 2* KPI like we run our super late model as you would have with the 13* KPI in the Triton. KPI = camber gain/loss.
Now something a little deeper to think about. I mentioned gain/loss but with the explanation above starting with 0* camber you only have camber gain when turning the the spindle either direction forward or rearward. If that makes sense???
So now let's start with a 13* KPI setup with 3* negitive camber and 0* caster in the RF spindle. Now you rotate the spindle forward slightly and you now have camber 0* camber. Rotate it slightly forward a little more and you now have 3* positive camber. Rotate that same spindle you started with 3* camber forward the full 90* and 13* positive camber.
I explained all of that with 0* caster because it is easier it explain what is happening with KPI. When you add caster into the formula it becomes a little harder to understand. I guess that is why they call it front end "geometry".
Also. I would like to mention that KPI in none adjustable and really has nothing to do with the inclination of the kingpin. KPI is the angle the spindle is welded to the barrel. If the KPI was 13* and you had 3* negitive camber in that spindle the
Feb 22, 2014
Weddle Racing said:
Can someone school me on the KPI when setting up a chassis? Im wanting to know what the angle of the kingpin does for handling, or what it does in general to adjust the angle of the kingpin. I know changing caster changes the angle of the kingpin, but thats about as far as that knowledge goes. Im trying to learn more about chassis setup to improve a few things. Thanks in advance for any help
lol, I just deleted a full page of stuff and I'll try it this way.
Easiest way to think about what it's doing is to think about if you would extend the kingpin on down, using it to point to a spot on the track. The spot it points to will be either towards the inside or outside of the RF tires contact patch and it will be either pointing ahead or to the rear of the RF tires contact patch.
It's an indicator pointing to where forces going to the RF are being projected. Your RF tire is then hung on a spindle. How the RF then will work with the track is influenced by where the force that is pulling it along the track is aimed. To keep the RF tire stable, it's generally going to be puled along by the kingpin, while it's also being pushed into the track by the kingpin.
Remember your the one who is turning the RF tire with the steering wheel. If you get the forces projected way far ahead of the RF tire, the tire will trail where the force is being projected. The more you let the RF tire trail where the kingpin projects, the more it will want to roll on it's own merry way in a straight direction and you'll have to input more effort with your arms to make it turn. Make it point straight down(KPI) and it'll still want to roll a little on it's own way because your still pushing on the RF tire in a turn, but not so much and maybe not so much that you will not even notice it. Make the kingpin point to the rear(which you'll probably never do) and the RF tire will be ahead of forces pushing on it and it will want to flop hellter skelter every which way. That's just about it either pointing to the front or more towards straight up and down or about how the RF trails where the kingpin projects.
Last is how it points left and right. That's mainly about when the kingpin is pushing the RF tire into the track. It's about how you are aiming the push at the tire contact patch. Do you aim it towards the inside of the RF tire, maybe dead center or possibly even a little towards the outside of the RF tire.
That's the easy part. The hard part is you want all the aiming done as needed, when the wheel is turned. And the forces that are going to the kingpin and being projected to the track can come from different directions.
So, ... you have your king pin pointing somewhere when the wheels are straight. Then out on the track you will need to turn the RF tire and have the contact patch of the RF tire presented to the track the way you want it. Then you have weight being sent to the RF corner in the turn. And you want that weight to be projected to the RF tire so it will work with the track as needed. Where your kingpin points is a reference(not exact but just a reference) for where weight is going to be projected. But how it's angled along with camber, etc., also sets up how the tire gets presented to the track when it's turned.
Complicated? yep. I'll post and read this, it's complicated writing about it too. Maybe I'll delete this too.
Quote mr south 59 and mr kish
