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
KPI (Kingpin Inclination Angle)
- Thread starter W5R
- Start date
The answer to "what is KPI" leads directly to another unanswered and relevant question which includes the answer to your KPI inquiry.
That, more inclusive knowledge would be the answer to "what is INCLUDED angle?"
You may call Hunter Engineering in St.Louis (Google 'em up) .....and ask them to send you their little manual....likely free of charge....on KPI, Included angle, and for that matter ackerman. These are all in the cagegory of "Steering Angles".
They have an 800# but I'll leave that to you, to take it from there.
Hunter Engineering
11250 Hunter Dr, Bridgeton, MO 63043
(314) 731-0000
Also...be SURE to have Mike McCarty's manual "Understanding Chassis Theory and Dynamics". McCarty's manual includes a GREAT tip sheet for what to do at the track to improve handling. If you understand all that's taught from these two sources, you'll be right up there with the late great Smokey Yunnick.
Hunter Engineering also runs week long classes for front end alignment, which is not free. Well worth your time and money, if serious about the subject.
Several of their instructors there can school you....(take one to dinner) on the effects of these angles, both static and dynamic.
Hunter Engineering is a magnificient facility......full of engineers and really smart people with lots of answers. Hope this helps! ....Paul D. (Power)
That, more inclusive knowledge would be the answer to "what is INCLUDED angle?"
You may call Hunter Engineering in St.Louis (Google 'em up) .....and ask them to send you their little manual....likely free of charge....on KPI, Included angle, and for that matter ackerman. These are all in the cagegory of "Steering Angles".
They have an 800# but I'll leave that to you, to take it from there.
Hunter Engineering
11250 Hunter Dr, Bridgeton, MO 63043
(314) 731-0000
Also...be SURE to have Mike McCarty's manual "Understanding Chassis Theory and Dynamics". McCarty's manual includes a GREAT tip sheet for what to do at the track to improve handling. If you understand all that's taught from these two sources, you'll be right up there with the late great Smokey Yunnick.
Hunter Engineering also runs week long classes for front end alignment, which is not free. Well worth your time and money, if serious about the subject.
Several of their instructors there can school you....(take one to dinner) on the effects of these angles, both static and dynamic.
Hunter Engineering is a magnificient facility......full of engineers and really smart people with lots of answers. Hope this helps! ....Paul D. (Power)
alvin l nunley
Site Supporter
When I decided to build karts, early 70s, I did some reading on kingpin inclination and caster.
I came away with the feeling that this information had little to do with karts.
With no kingpin inclination, and no caster, the wheels on the front of your car would have a tendency to wander all over the place. Kingpin inclination creates an arc, and the wheels center on the top of that arc. When you turn the wheels, both wheels go down raising the car. In the early years of automotive development there was no power steering, and this raising of the car made steering harder. Negative caster helps make it easier to steer. Now how that stuff has anything to do with helping a kart handle is beyond me.
When designing my 1st kart, I decided a kart didn't need kingpin inclination. The fact that the bug kart, at that time, didn't have kingpin inclination, only reinforced my belief. I didn't sell a lot of those karts but the ones I did sell, the people that bought them were very happy with them.
With positive caster, kingpin inclination will add to the caster effect on the inside tire, and subtract from the caster effect on the outside tire.
I think the reason all karts have kingpin inclination is because of this; if you build a kart that doesn't have it, and somebody is not happy with the handling, the 1st thing they probably would tell their friends is "it's because of the lack of kingpin inclination!!!"
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
I came away with the feeling that this information had little to do with karts.
With no kingpin inclination, and no caster, the wheels on the front of your car would have a tendency to wander all over the place. Kingpin inclination creates an arc, and the wheels center on the top of that arc. When you turn the wheels, both wheels go down raising the car. In the early years of automotive development there was no power steering, and this raising of the car made steering harder. Negative caster helps make it easier to steer. Now how that stuff has anything to do with helping a kart handle is beyond me.
When designing my 1st kart, I decided a kart didn't need kingpin inclination. The fact that the bug kart, at that time, didn't have kingpin inclination, only reinforced my belief. I didn't sell a lot of those karts but the ones I did sell, the people that bought them were very happy with them.
With positive caster, kingpin inclination will add to the caster effect on the inside tire, and subtract from the caster effect on the outside tire.
I think the reason all karts have kingpin inclination is because of this; if you build a kart that doesn't have it, and somebody is not happy with the handling, the 1st thing they probably would tell their friends is "it's because of the lack of kingpin inclination!!!"
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
jack burroughs
member
Kingpin inclination in the form of high castor makes anything handle better at high speed, hence early rails used up to 45* castor, but the wheels are more subject to high speed wobble then when the advent of power steering got to almost all cars on the road they could handle negative castor to reduce the tendency to shimmy. From Bear Alignment handbook.
Mr South 59
New member
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 kingpin angle would be 16*.
Hope this helps
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 kingpin angle would be 16*.
Hope this helps
paulkish
old fart
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.
paulkish
old fart
after all that I think I can say it short...
KPI will effect handling because changing KPI alters the weight available to be projected to the RF. It also alters how weight is projected to the RF, when the RF tire is turned and pushed into the track. Changing KPI will also change RF tire presentation when the RF wheel is turned, as Mr South 59 explained.
I think it's very complicated. I also think how fronts on LTO's are used has nothing at all to do with how passenger cars are aligned and how front ends on karts which turn both left and right are setup.
KPI will effect handling because changing KPI alters the weight available to be projected to the RF. It also alters how weight is projected to the RF, when the RF tire is turned and pushed into the track. Changing KPI will also change RF tire presentation when the RF wheel is turned, as Mr South 59 explained.
I think it's very complicated. I also think how fronts on LTO's are used has nothing at all to do with how passenger cars are aligned and how front ends on karts which turn both left and right are setup.
alvin l nunley
Site Supporter
I don’t think is very complicated at all.
But I disagree with your thought that LTO front geometry and Sprint geometry are not the same. The only dissimilar thing is the fact that the Sprint kart has to turn both ways. Left and right. The LTO kart, as its name implies, only turns left, so the geometry can be optimized. The fact that it is optimized for, “left turn only” doesn’t make the principle different, only the application. The fact that LTO karts can be adjusted, without major changes, to race Sprint, should prove that.
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.
alvin l nunley
Site Supporter
I’m not sure that’s true or not, (the angles) it could be, (the fact that you can’t turn the front wheels 90 degrees might prevent you from proving it) but the fact that the same thing happens on both sides, means, one side cancels out the other. The only thing that camber does; it centers the wheels in the middle of the arc. Like I explained earlier.
Go to Wikipedia, the illustrations are there for everyone to see. I didn’t dream any this stuff up, I got my information from people who really know!
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.
Mr South 59
New member
I know for sure!!!
Al that is why mentioned the mockups. On a mockup you can turn the spindle 360°. You can change KPI, camber, and caster and measure any angle in any position. I also mentioned the amount/timing of the camber gain on that spindle. Because on an LTO kart under racing conditions the spindles only rotate between 3*-7*.(the 7* is usuilly to the right). If you need the amount/timing of the camber gain to be more or quicker you will need more KPI angle. If you need less camber gain you will need less KPI.
And Al. It is not a fact that both sides do the same thing. They don't!!! Like the Triton. It has different KPI on both sides. It also runs better with 4* caster split. So with the RF having a lot more KPI angle it also has 4* more caster. And it likes 4* camber and the LF likes about 0*. And like Paul would mention , the RF and LF have totally different forces on them. The geometry is nothing alike from the left front to the right front. The forces are nothing alike. So how could they react the same way on both sides Al?
And Al. LOL If you really think that the only thing that camber does is, it center the wheels in the middle of the arch. LOL You really need to quit reading Wikipedia and buy a real gokart. And please don't give any frontend geometry advice until you do. You really don't get it!!!
Al that is why mentioned the mockups. On a mockup you can turn the spindle 360°. You can change KPI, camber, and caster and measure any angle in any position. I also mentioned the amount/timing of the camber gain on that spindle. Because on an LTO kart under racing conditions the spindles only rotate between 3*-7*.(the 7* is usuilly to the right). If you need the amount/timing of the camber gain to be more or quicker you will need more KPI angle. If you need less camber gain you will need less KPI.
And Al. It is not a fact that both sides do the same thing. They don't!!! Like the Triton. It has different KPI on both sides. It also runs better with 4* caster split. So with the RF having a lot more KPI angle it also has 4* more caster. And it likes 4* camber and the LF likes about 0*. And like Paul would mention , the RF and LF have totally different forces on them. The geometry is nothing alike from the left front to the right front. The forces are nothing alike. So how could they react the same way on both sides Al?
And Al. LOL If you really think that the only thing that camber does is, it center the wheels in the middle of the arch. LOL You really need to quit reading Wikipedia and buy a real gokart. And please don't give any frontend geometry advice until you do. You really don't get it!!!
Al, take an oval kart to a road course that runs clockwise and let me know about your success. Even a counter clockwise track with a couple 180* corners will quickly put your claim to rest.
I also agree with Paul in that differences in oval and sprint karts are significantly different in regards to front end geometry, mostly in regards to ackerman. Simply swapping the steering shaft from a sprint kart and oval kart would have significant negative effects to each.
I also agree with Paul in that differences in oval and sprint karts are significantly different in regards to front end geometry, mostly in regards to ackerman. Simply swapping the steering shaft from a sprint kart and oval kart would have significant negative effects to each.