Chassis math formulas

9

95 shaw

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I thought a place for formulas for chassis math problems would be nice.

I think most can find percents from wheel weights.
Yes, I know some have spreadsheets for this. I just feel I get a better understanding of what happens when using a piece of paper and calculater .
Please post your formulas here.
 
Lateral weight transfer can be calculated anywhere in a corner.

[(Total weight × center of gravity height) ÷ track width] × g force = amount of weight transferred laterally.

Same formula works for front/rear transfer.
 
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Chassis wheel weights can be calculated from total weight and percentages.

First calculate weights from percentages

Left = total times left percent
Front = total times front percent
Cross = total times cross percent

Right front wheel weight can be calculated

If cross is greater than left then add difference to front weight and divide by 2
If cross is less than left then subtract difference from front weight and divide by 2

Once rf wheel weight is known, simple subtraction from known weights will give all other corner weights.
 
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I envy your math skills, and your skill with a calculator, pen/pencil, notepad. I envy that you have the time to do all this. I can't imagine why somebody would want to do this, when the spreadsheet is so much quicker and more accurate (just a guess), but whatever.(quote)

I tried to address this in the opening post. I answered the why in this thread. Post 32
http://karting.4cycle.com/showthread.php?80852-Question/page2
 
For theoretical analysis, transfered weight can be divided front and rear using the front weight percentage

Multiply the total amount transfered by the front percentage to get amount transfered at the front.
Subtract this amount to get weight transfered at rear.

For left turns add front transfered weight to right front static weight. Subtract from left front static weight.
Do the same at the rear.

The results will be new wheel weights after weight transfer.

This will allow you to see the effects of making changes to left, front, cross, center of gravity height, and track width during cornering. Understanding the effects should help make seeing why a particular change affected the chassis.

This is without any input of tire lateral grip performance, which is another can of worms.
 
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If you're following along., you may have noticed the weights are not what you expected if you Used numbers from a setup you know works on your chassis.

Typical thought is the numbers added together should be close front and rear. Although this gives a picture of what is happening, it's not the whole story.

Some useful information can be had with what we now know.

If you've played with the g force numbers to the extreme, you have noticed left side tire weight can go to zero or below. Center of gravity height extremes can cause this also.
Coke syrup racers can relate to this phenomenon. It can get exciting.
 
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Tires

I know most chassis discussions begin with the tires. As these four small contact patches are your chassis only link to the track, That is a pretty good place to start.
As I am a mechanic for a road construction dirt contractor, I've always felt changes to the road were harder to make with traffic already on the road.


So here we are.

You can calculate the size of the contact patch of each of your tires.

The weight on the tire divided by the air pressure in the tire will give the area of the contact patch.

Notice I never said anything about the width or size of the tire. These are not factors in determining area of contact patch.

The width of the tire will help determine the shape of the contact patch. As we in the lto world use 3 or four different width tires, this makes a considerable difference.

Since area = length times width, and knowing the width of the tread on the tire, we can determine the shape of the contact patch.
This holds true both static and dynamic for computational purposes. We'll get into the actual shape in the dynamic mode later.
I find it easier to visualize if I draw those shapes on 4 sheets of paper and set them as they would be on the kart . Drawing both static and dynamic will make things more clear.
 
chassis tuning sheets

If you have your contact patches drawn, and are wondering what to do with them, good.

Chassis tuning is, pure and simple, the manipulation of those contact patches.

Changes in the size and shape of these patches will alter how our chassis reacts.
I would take this time to look at what specific changes do to the contact patches. Changes in air pressure will be the easiest to see.
The nogoats tuning sheets will give you changes to make and the directions they are going to go. I recommend getting them if you don't already have them. they are available at:
http://nogoats.net/

If you familiarize yourself with changes and effects, some of the next things will be easier to see.

I am not opposed to using spreadsheets to speed the process, I just feel if you don't know how the numbers are generated, they are not going to do much good. Make your own or get someone else's to help your process.
 
Dirt LTO chassis race with both high and low cross setups. It is sometimes helpful to look at each one of these to compare what the chassis adjustments do. If you don't have one in mind, there have been several discussions about these here. A search will give a baseline to play with.

If you have a good baseline setup already, the calculations can be used proactively to have changes ready if needed. A driver change with the same weight, but different heights comes to mind. A change in center of gravity height would be caused.
Start with your baseline and original driver. Then calculate with other driver. Now figure what changes need to be made to get back to the same dynamic contact patches as before. Or at least a reasonable approximation of those.
 
I tried not to make too many assumptions or conclusions in this thread. I wanted others to use the info provided and draw their own. If this has been helpful, then mission accomplished. If not, I tried not to waste too much time.

I posted all of this because I need a base for some other things I want to talk about. Those involve my own conclusions so I will move them to another thread.
Thanks for putting up with me.

If I can figure out how to edit some of my old posts, I'll try to clean up some of the info and spelling/ punctuation errors. I'm blaming my dumb smart phone.
 
If you have any chassis math calculations you would like too add, feel free to do so.
If I made any mistakes or had problems with my presentations, please tell me and I'll try to fix it.
 
95 shaw said:
If you have any chassis math calculations you would like too add, feel free to do so.
If I made any mistakes or had problems with my presentations, please tell me and I'll try to fix it.
Click to expand...

Left rear dragging, right rear dragging, I would like to see this resolved. The idea, that a right rear that is skidding along with a left rear that is planted, and this is helping you go faster, just doesn't sit well with me.

If you could find a long enough piece of dirt, and driver a kart, with stagger, straight down that dirt track, and when you stop, check the tire temps, then you would know.

If the left rear is planted, and the right rear is spinning, it takes energy to spin that right rear tire, it doesn't add energy and make you go faster. That's crazy. Why do you suppose a staggered rear axle makes a kart want to turn left? A spinning tire has a lot less traction than a rolling tire. That's why they have antilock brakes.
 
It's not spinning wildly. 1 inch every 34 is a long ways from that.
Part of the way tires make grip involves slippage to some degree. Besides 1 tire or the other has to slip.

Do the work. Study a little. You claim to have the tools. They do little good in the box.
 
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I suspect even a carefully conducted test under your direct supervision that did not yield the results you wanted would elicit the exact same response.
 
can you send me that spreadsheet, I would like to use that.
alvin l nunley said:
I envy your math skills, and your skill with a calculator, pen/pencil, notepad. I envy that you have the time to do all this. I can't imagine why somebody would want to do this, when the spreadsheet is so much quicker and more accurate (just a guess), but whatever.

One of the things that I like about my spreadsheet is the ability to do "what if's". What if I put two pounds more on the left front? Put the cursor in the left front cell, add two (or whatever) hit return, and there's your answer. Total kart weight, all three percentages (front, left, cross) front to back and LF to RR cross plus percentages and weight on the front cross and the rear cross. Don't know if the FC or RC will do you any good, but they're there.

Or; put in Front Left and Cross Percentages that you desire, and it tells you what each wheel needs to weigh to make those percentages.

Or; put in the individual wheel weights and it tells you what percentages you have.

Best of all, no errors. Ever.

Send requests for a free, fully operational, copy to anunley@austin.rr.com It will not work in a handheld phone or whatever, you need a computer. Desktop, laptop, either one.

There's 29 spreadsheets in what I call Nine Sheets. Lots of karting related stuff. To be fully compatible you need Excel 10, but the generic spreadsheets work pretty well, all except the macros. You have to rewrite the macros for generic spreadsheets.
Click to expand...
 
The best way to make me see your points of view ist to use my own method to dispel my conclusions. Or show my method is faulty.
I have already welcomed that.
 
Give the percentages and air pressures you used, along with the areas of both rear contact patches in the static mode. Then explain the flaw in the method.

Or not. Again it really doesn't matter.
 
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