Very good, you’re doing your homework.
Here’s a picture of what happens when you add kingpin inclination. The spindle on the left has 12° caster with 10° kingpin inclination. The spindle on the right has only 12° caster with no kingpin inclination. Look at the numbers.
Everything is relative. It doesn’t make sense to compare caster settings between two chassis because every frame design is different and materials are different.
In terms of tuning, it doesn’t make sense to compare your caster setup to a different kart. They may work in completely different ways.
Unfortunately it is not clear to me. What these numbers means?
[quote=“JR_Garcia, post:23, topic:6854, full:true”]
Unfortunately it is not clear to me. What these numbers means?
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Exactly what is it you don’t understand? Do you not understand caster? Do you not understand kingpin inclination? Do you not understand the purpose of each?
How about a bit of verbal explanation of your pretty coloured pics for the benefit of the ‘thicker’ ones amongst us.
Also an illustration/explanation of what the other (lh) stub axle is doing?
I understand caster and kingpin inclination as well as the interaction between both. It is not so complicated for an engineer. What I could not understand was your drawing and the numbers (0.6206 and 0.6785) you presented there. The drawing is not self-explanatory. So I agree with @d-i-y80 it would be good to have a written explanation of the pics.
So much for the adage; a picture is worth 1000 words!
Explain to me what you don’t understand!
Explain to me what you don’t understand about him not understanding.
I said I didn’t understand the meaning of the 0.6206 and 0.6785. What unit are?
Notice the part I have drawn intersecting the Centerline of the axle stub. That is what kingpin inclination does. My thinking, and experience has proven me correct, is that you don’t need kingpin inclination when you have that much caster… Kingpin inclination keeps the wheels Tracking a straight line, It’s not needed when you have is much caster is we have in our karts. Caster does the same thing as kingpin inclination and I have found that inclinatioon is not needed.
So I want to understand the reasoning behind why manufactures use kingpin inclination if it is not truly necessary? Thinking about the dynamics of how the angles change during the pivot of the stubs axles:
With 0 caster and only negative (leaning inward) king pin inclination, would the stub not drop in either direction as it rotates away from center?
Now keeping that same negative kingpin inclination, if you were to start to increase the caster angle (move top of kingpin toward the rear), would the end of the stub axle drop more in the rearward pivot than the forward pivot? If so, does this not affect the overall weight transfer of the kart? Is this not a way of increasing the rate of change of the inside wheel and decreasing the rate of change of the outside wheel when turning?
Could this be used as a way of keeping the outside tire’s contact patch more parallel to the surface? Thereby increasing grip to the unloaded corner?
***(Thank you John, edit made)
I’m dying to know more about this as well. Thinking about it for a bit has put my brain in a pretzel. I’d venture to guess that it has as much or more to do with the outside front as it does the inside front. With Al’s example of zero KPI, but more caster, it’s going to create a pretty violent jacking effecting due to increased vertical movement of BOTH sides (in opposite directions).
In thinking about your question about no caster, but still having some KPI, it would still create downward movement of the spindle as it rotates, but the difference is that it would be across a perpendicular plane to that of what we’re used to with modern kart construction. Easiest way to visualize this is to imagine a standard spindle configuration, but with zero caster and some amount of inward KPI…now rotate that spindle 180 degrees (theoretically), and there you go.
So this would lead me to GUESS that modern karts having KPI is to help balance the vertical movement of the spindle, specially to control the rate for each respective side (again coming back to my theory about the outside front). Couple this with other aspects of modern kart geometry, specifically Ackerman on the steering column, and these all work together to make these turds turn left and right.
I could be way off base here, but who knows.
Another good point, as this allows the inside front to turn in further than the outside front thereby making the inside responsible for most of the weight transfer. Otherwise at the extreme, the outside front spindle could raise to the point that is allows the frame to drop and contact the road surface.
It would seem in this thought experiment that although King Pin Inclination is not necessary, it does serve a purpose especially when combined with Ackermann Steering Geometry.
BTW, thanks to @NikG for breaking out the angle finder and @alvinnunley for the great graphics. They really helped me visualize what was happening.
someone asked about what happens you turn the wheel ri to the right. This is an illustration. Notice the black line intersecting the end of each axle. Of course this isan exaggeration, the spindle is turned 40° in each direction. Far more than you would turn it during a race.
Does this exaggerated image help?
So, caster helps both front wheels to go to different directions vertically speaking, it means, while the inner front wheel goes down and pushes against the ground, the outer front wheels goes up, what create a inclination to the front end of the kart and helps to get inner rear wheel lifted.
In the same time KPI influence in the way a wheel goes from a position A to a position B creating an arc. So, why we need this arc? Why not going straight from position A to position B?
That’s the question I asked myself when I built my first kart in 1973 almost 50 years ago. I decided it was not needed and I was proven out. That kart handled as good or better than any kart I compared it to.
Look at a photo of Al’s kart(s) from long ago, and compare with modern era karts. A couple of big differences that stick out to me are 1) scrub radius and 2) front track width. Couple that with a drastically different tire, and probably some difference in chassis material, and I’d say all of these are contributing factors.
I’d be curious to know when manufacturers started utilizing KPI, or has it always been the case?
I raced for a friend back in 2013/2014 aboard a modern chassis that he designed and fabricated. Old photos tell me that his chassis had some KPI built in, so I’d be curious to get his take on why this seems to be an integral design feature.
Where did you see a picture of my kart? 1973/1975 Mayko Shark.
Post a cool Pic of you in your Kart
Regardless of whether this is the exact chassis, the point is that karts of that era were much different in the ways of track width and scrub radius than the karts of today.
