Chassis math formulas

[alvin l nunley]

Try these

Thank you.

It's hard to tell from those views, (not the picture, there pretty good, but the angle) but that first picture definitely shows, to my view anyway, that the top of the kingpin is outside the wheel. I'm going to include a couple of new drawings that I made which better represent what I've been told.

To better suit the critics, I have increased the kingpin inclination, in the first picture, to 12°. In my picture, both the top and the bottom of the spindle are inside the wheel. The point I was trying to make is; the scrub radius does not change with a change of kingpin inclination. On a typical kart, kingpin inclination has no effect on scrub radius as defined by Wikipedia.

I think when speaking of scrub radius, they're talking about a kingpin that has very little caster. With a kart, because of the large amount of caster, the scrub radius, as defined in Wikipedia, wouldn't even be on the bottom of the tire! I'm going to have to do some three-dimensional drawings to show where it's at. I don't even have to look to know it's not on the bottom.

Now, if you want to change the definition of scrub radius, as defined in Wikipedia, we could have that discussion.

 

[95 shaw]

My caster turns to camber was a simplification instead of saying with a near zero scrub radius, the major effect of caster is not weight jacking, but the increase in caster.

The last word should have been camber.

 

[paulkish]

The whole premise is to realize that weight is transfering, and that weight transfer has to be accounted for when tuning and viewing what the changes do. Its just a method for looking at things. in no way is it accurate all the way around the corner as the g forces change all the way through the turn. The point was to be looking at what changes do to the contact patch to see what happens when a change is made. Its simply a tool. If you had read the whole thread, I stated that at the end to allow you to make assumptions of you own.
If it doesn't work for you, not a problem. just a way to look at things.

My comment has nothing at all to do with assumptions and how to look at things. It's a statement of how the formula you presented in your second post, has no validity when considering how LTO's with stagger and a solid axle work. I will give you that moving a LTO's ability to use it's stagger and solid axle towards being totally useless for their intended purpose, moves the formula you presented closer towards reality. The reality is your formula is incorrect unless a LTO looses all ability to use it's stagger and solid axle.

I do understand though you and others can use it for something to relate too. But I still see your second post to be trying to show how a lefty righty formula applies to a LTO which is not used like a lefty righty. And your whole premise of presenting it is based on incorrect information and belief of how LTO's work.

Your adding up numbers correctly and getting a correct answer, but the numbers your using have nothing at all to do with the application. ... and I'm not arguing the numbers, I'm arguing and trying to correct your thought process. ... maybe??????????????/

 

[flattop1]

You are right Al. The top of the king pin is outside the wheel, the bottom is inside the wheel.
That new representation is quite close.
This one is from! The bottom.

 

[95 shaw]

My comment has nothing at all to do with assumptions and how to look at things. It's a statement of how the formula you presented in your second post, has no validity when considering how LTO's with stagger and a solid axle work. I will give you that moving a LTO's ability to use it's stagger and solid axle towards being totally useless for their intended purpose, moves the formula you presented closer towards reality. The reality is your formula is incorrect unless a LTO looses all ability to use it's stagger and solid axle.

I do understand though you and others can use it for something to relate too. But I still see your second post to be trying to show how a lefty righty formula applies to a LTO which is not used like a lefty righty. And your whole premise of presenting it is based on incorrect information and belief of how LTO's work.

Your adding up numbers correctly and getting a correct answer, but the numbers your using have nothing at all to do with the application. ... and I'm not arguing the numbers, I'm arguing and trying to correct your thought process. ... maybe??????????????/

I'm really at a loss how a Lefty/Righty formula does not apply to Lefty only. Weight still transfers regardless of which way we are going.
What I presented requires no change in anything you are currently doing. It is simply a different way of looking at things. It makes sense of adjustments. The stagger is still used as you feel is intended.

I made a post about a segway with a staggered axle with perfect stagger. I think that applies.

It really does not matter. As I stated, these are just my thoughts.

 

[95 shaw]

Thank you.

It's hard to tell from those views, (not the picture, there pretty good, but the angle) but that first picture definitely shows, to my view anyway, that the top of the kingpin is outside the wheel. I'm going to include a couple of new drawings that I made which better represent what I've been told.

To better suit the critics, I have increased the kingpin inclination, in the first picture, to 12°. In my picture, both the top and the bottom of the spindle are inside the wheel. The point I was trying to make is; the scrub radius does not change with a change of kingpin inclination. On a typical kart, kingpin inclination has no effect on scrub radius as defined by Wikipedia.

I think when speaking of scrub radius, they're talking about a kingpin that has very little caster. With a kart, because of the large amount of caster, the scrub radius, as defined in Wikipedia, wouldn't even be on the bottom of the tire! I'm going to have to do some three-dimensional drawings to show where it's at. I don't even have to look to know it's not on the bottom.

Now, if you want to change the definition of scrub radius, as defined in Wikipedia, we could have that discussion.

My only disagreement with the last drawing is where the center of the contact patch actually is. In static mode, as drawn, depending on air pressure and load on rf tire. maybe only half of the tire face is actually in contact with the track surface. In dynamic mode, slip angles and tread distortion should be accounted for. Lots of things to think about.

Good drawing though.

 

[alvin l nunley]

Here's a couple of more drawings. One is from the back of the RF tire and shows that the spindle is pretty far into the wheel. The spindle has 12° of kingpin inclination and 12° of castor. In this drawing there is no camber angle on the tire. The point I am trying to make is; the intersect point of the kingpin bolt is toward the front of the tire, not even on the ground. I'm not knowledgeable enough to speculate on what that means, but it's sure not like the picture that's in Wikipedia. Their picture indicates, to me anyway, a spindle with no caster. Definitely not one with 12° of castor.

 

[alvin l nunley]

Scrub radius
From Wikipedia, the free encyclopedia

The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road.

So, I needed to reevaluate my understanding of this, and after consulting with Wikipedia, I find I really didn't have a very well-founded understanding. So much for looking at pictures. lol

Now I'm having trouble deciding where the tire contact patch is, on a 10 inch tire, with 3° negative camber.

That contact patch, obviously, has more weight on the edge, with less and less weight as you continue across the tire. That "patch" is going to grow and shrink as the camber increases/decreases, as the air pressure increases/decreases and as the weight of the wheel increases/decreases. To even further complicate the computation, on a kart, because of castor, that line through the spindle does not pass through the tire where the tire is contacting the ground. How that effects the calculations I have no idea.

I don't have any idea how much caster there would be in a full-size car that races on the dirt. My best guess would be that it's a lot less than a kart. My best guess; this would further separate the usefulness of comparing a car to a kart. Amongst other things.

Further drawings to follow!

 

[paulkish]

Yes it is complicated Al. It becomes more so because your now considering for example the RF, in terms of function not just math. To do so the new found complications must be blended with forward slip ratio and a real lateral slip ratio. Contact patches constantly change no matter what math is used to define their potential size and shape. No matter what you use or what path you take to get to the tire contact patch, it's use can only be defined by blending forward and a real lateral slip ratio. Yes there is a definition for the combination of both forward and lateral slip ratio, but it escapes me now. And I have learned to not use it because it lacks including concepts I need for myself to see my own picture. What it is that is missing from the sometimes use reference combining both forward and lateral slip ratio, right now I don't remember. 95 shaw, I think if you take the time to find the somewhat common reference, you'd find it fun reading. ...

Yes it is very complicated.

Formulas are nice but application is about making a tire work as needed. My quest is to learn how each tire needs to be use not only at each point around the track but how to use each tire through one portion of the track to enhance the next.

Knowing the workings of the chassis which allows forces to be applied trying to give the tire a specific contact patch gets even more complicated when you bring in the mechanics of the tire and the track.

The 'art' of today's racing Al is more about knowing how tires need to be used differently all around the track to most efficiently move your LTO along the track. Next the most historically efficient mechanical setup is given to what your LTO racing. The final brush stroke and key in the art of LTO racing today Al is then being able to adjust each tire your using as needed. To not just cause a needed contact patch, but to make the contact patch you have available, able to give neither too much nor too little needed grip/bite at all places around the track.

In the racing LTO 'art' world of today Al, all things of yesterday and history are needed canvas background, with varying tire brush strokes covering background where needed and defining the picture.

In simple; today Al it's all about tires. ...

 

[95 shaw]

It's been said, a picture is worth a thousand words, even moreso, the correct picture.
I'm glad we could help.
Yes, the strategy is different on a dirt racing car, depending on class and car. Arriving at the picture you have works exactly the same.
I have run as much as 12 degrees caster. The required spindles (stock) have 8 degree kingpin build angle.
The suspension adds even more complications. The effect is still to have the right amount of traction at the correct spot.

 

[JWD]

I think you have all wasted a lot of karter's time.

 

[alvin l nunley]

Yes, the strategy is different on a dirt racing car, depending on class and car. Arriving at the picture you have works exactly the same.
I have run as much as 12 degrees caster. The required spindles (stock) have 8 degree kingpin build angle.

I'm having trouble seeing that, can you better explain?

 

[95 shaw]

The mustang II spindle have an 8 degree kingpin inclination. I just described it differently. sorry.

 

[krtrcn]

I have a question.
In all these post not one time has the size of a driver.
I know when I do my set up I'm in the kart, because if I'm not all my numbers change, including camber. What if I put a set of tires on that the right side has camber cut it to them, or rounded outside shoulders for a little more side bite. If I run higher air pressure wouldn't that or could that change my contact patch.
What about the math formula then, or is this a perfect world setup, and let's not forget driving style. "Loose,tight, neutral"
?

 

[95 shaw]

The math formula is just a tool to help learn what the adjustments do. Air pressure is one of the tuning changes commonly made. Camber also changes the shape of the contact patch. The size of the driver changes the vertical center of gravity. The whole idea is to be thinking about how these things affect the contact patch. It is by no means a way to arrive at the perfect setup at all times. The goal was to make assumptions of your own based on what you saw at the contact patches. Tuning is sometimes easier if you look at things differently than you were before.

 

[krtrcn]

That's why I keep a note book.
That's also why chassis manufacturer give you different setups according to your class, and you can tweak it from there.
I just don't understand why some people get on here and can make things so complicated, especially for someone just starting out.
The best way to learn how to set up a kart is trial an error, and a whole lot of set time. He'll my first season if I didn't get lapped their was something wrong.
The biggest thing I'm trying to say is keep it Simple, so everyone can understand.

 

[95 shaw]

That's why I keep a note book.
That's also why chassis manufacturer give you different setups according to your class, and you can tweak it from there.
I just don't understand why some people get on here and can make things so complicated, especially for someone just starting out.
The best way to learn how to set up a kart is trial an error, and a whole lot of set time. He'll my first season if I didn't get lapped their was something wrong.
The biggest thing I'm trying to say is keep it Simple, so everyone can understand.

If you look at the posts above, some cannot see if even explained like this.

Some would like to understand concepts that just get a passing "everyone should know that". It's hard to explain if you don't have some background. That's been my reason for doing this.
Sorry for wasting your time.

 

[95 shaw]

Also, some do not live in the Mecca of racing. 6-8 races a year, 1 class, does not grow your notebook much.

 

[krtrcn]

I've been in this sport for over twenty years, so what when it comes to knowing what my kart needs to do I think I know what to do. I chalk this up to seat time, and not over thinking things.

I've also been taught if you can't say anything good about someone not to say anything at all.
Well I'm going to follow that rule because it obvious that know it all.

Have a nice day.

 

[95 shaw]

Here it is.

The lateral weight transfer formula (post 2), and several others. came from "How To Make Your Car Handle" by Fred Puhn.