Track Tac

Spindle Angle

I think we can all agree, the kingpin is the center of rotation for the spindle.

We can also agree, regardless of caster, camber, KPI, there is no vertical movement at the center of rotation, or along that axis.

There can be no weight jacking without camber change
 
Last edited:
Now thats a loaded statement.
Weight jacking in the fourm of loading or unloading ?
My initial thought is caster alone will do it .
Which in itself would create some camber change .
I need to ponder on this .
 
95 shaw said:
There can be no weight jacking without camber change
Click to expand...
I guess it depends on your definition of "jacking"! We might have different definitions. My definition is this; when you turn the wheel, on a left-hand turn, because of castor, the left wheel goes down and the right wheel goes up. "Jacking". This should take weight off the LR. That is what I call "jacking". What's your definition?
 
alvin l nunley said:
I guess it depends on your definition of "jacking"! We might have different definitions. My definition is this; when you turn the wheel, on a left-hand turn, because of castor, the left wheel goes down and the right wheel goes up. "Jacking". This should take weight off the LR. That is what I call "jacking". What's your definition?
Click to expand...
Same as yours.

Just working on one wheel for the moment.

Can there be weight jacking without camber change?
 
Last edited by a moderator:
Lto the left does all the jacking . Nothing is constant , the right would do some jacking with reverse caster .
A gain in camber would increase that jacking amount .
Sidewall deflection would reduce that gain .
Contact patch change may be the bigger difference .
 
Yes.

That was the point I was coming to.

There can be camber change without weight jacking.
Camber has a lot to do with it. Kingpin inclination is a key factor.

1573082679421.png

Here is a picture of it.

For turn in in the range we use, camber will change slightly, but little weight will come off the rf tire.
The point is not to unload the most powerful tire to help turn into the corner until weight transfer adds more load to the tire.
Kingpin inclination also keeps the amount of camber gain at turn in low.
 
Last edited:
flattop1 said:
Lto the left does all the jacking . Nothing is constant , the right would do some jacking with reverse caster .

Contact patch change may be the bigger difference .
Click to expand...
Can you imagine a teeter totter where only one end of the thing goes up and down?
The left tire goes down and the right goes up. This causes a pivoting movement with the pivot point being a theoretical line drawn between the LF and the RR. Kind of like a teeter totter.
Can someone tell me how that is affected, dynamically, by camber? Now I realize that camber can, by itself, cause an increase in that teeter totter motion, but only if you don't adjust your corner weights to compensate for the change in camber.
 
1573088239159.png

This is camber change.
As the end of the spindle swings through it's arc, regardless of static camber, the angle of the tire must change relative to the chassis, thus camber change.
If the outside end of the spindle goes up, more negative, or less positive, camber.
 
Last edited:
alvin l nunley said:
Can you imagine a teeter totter where only one end of the thing goes up and down?
The left tire goes down and the right goes up. This causes a pivoting movement with the pivot point being a theoretical line drawn between the LF and the RR. Kind of like a teeter totter.
Can someone tell me how that is affected, dynamically, by camber? Now I realize that camber can, by itself, cause an increase in that teeter totter motion, but only if you don't adjust your corner weights to compensate for the change in camber.
Click to expand...
If you look at your database of chassis setups for lto karts, you should notice some with high cross.
Our chassis are a large flat spring, cross is just preloading the lr/rf spring. When the lf raises that corner of the chassis, we are simply unloading that spring. We wish to maintain or gain weight on the rr/lf tires. To maintain steering, we must minimize losses at the rf until weight transfer increases the weight here. The goal is not to lift the lr tire off the ground. Thus no teeter totter.

See stagger for why not lift the lr off the ground.

This is also why it is important to analyze changes completely to the contact patches.
What you think is happening may not be even close to what is actually occurring.
 
Last edited:
To get back to the OP second question:
How or when to change spindle kingpin inclination.
1573133644295.png

12 degrees caster/zero KPI
1573133759991.png

12 degrees caster, 12 degrees KPI
 
1573133929992.png

0 degrees caster, 12 degrees KPI

If we change spindles to 10 degree KPI, this curve becomes less exaggerated (larger radius) therefore, less camber change
 
Last edited:
1573134160496.png


If we change to 10 degree KPI spindles, the spindle axis moves closer to the inside edge of the tire. (moves the center of the contact patch away from the spindle axis).

Maybe we can talk Alvin into drawing a 10 degree Kpi, 12 degree caster curve to help the original poster?
 
Last edited:
Sounds like some of y'all need to go look up Paul van Valkenburg....
https://www.amazon.com/Race-Engineering-Mechanics-Valkenburg-1993-03-07/dp/B01N8Y0ZV7
Even if the chassis doesn't actually "teeter", the flex induced makes it act like it does. The goal is to reduce just enough load on the LR to prevent too much loss of speed due to friction and to prevent it from fighting the driver's input at the front end to make the kart turn in. However, since it can still assist overall grip level, we don't want it off the ground unless the conditions are such that the RR can handle all the load. ( UAS, ymmv.) The waist of the kart is where the predominant flex characteristics are determined, and the tubing diameters determine the spring rate/s that the geometry of the waist is working through... The chassis is a giant spring, with the loading determined mostly by the inertia of the VCg of the driver, and the tires attempting to negotiate between available grip and driver input... The trick is to know when your RF is under loaded vs. overloaded... And then what to do about it. Something to think about -- can the RF be "overloaded" but stagger negate the usual apparent signs? What does that mean for straight line speed? I'm glad this thread is continuing on...
 
Good points, Ted.

Right now trying to work at one wheel (rf) to show how and why we use KPI. then we can move on to other parts of the setup and chassis design.

If we can keep on subject, and keep those perpetuating a zero KPI theory on board long enough to put either theory to bed, maybe we all can learn something, instead of covering the same ground over and over.

My thinking is when suggesting something repeatedly, I should have a good understanding of how the current theory is being used, and how I believe my suggestion will work in it's stead.

By the way, I have the '93 edition of that book.
 
Last edited:
You must log in or register to reply here.
Back
Top