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Center of Gravity Height Again
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Author:  ky mustang [ Thu Oct 01, 2009 4:48 pm ]
Post subject:  Re: Center of Gravity Height Again

I will try to explain this. Your suspension is mounted under the COG. It will always try to drive under the chassis and lift the back of the chassis.

What loads and controls how much the suspension can lift the chassis is where the ic is located. Every chassis has a neutral line. Where the line passes represents an equal amount of weight on top and below the line. The weight is transferred through inertia not actually moved when the car launches.

If your ic is located below this line more of the weight will be on top of the line leaving less to be transferred on the bottom half . Its not going to be an equal load so this would resist the suspension wanting to separate /lift the rear more and compress the springs and cause squat .

Author:  Beretta [ Thu Oct 01, 2009 5:18 pm ]
Post subject:  Re: Center of Gravity Height Again

I use a program and it does the CG for you but it may not be correct as it don't ask how much your car weigh's :-s ...Looks like it's says that the cam is about CG but that can't be right :-k .... How does the rising the back of the car help find the CG???????

Now when I scale my car VP told me just make the left front 30 to 40 lbs heaver than the right....I have done this and never had any problems with it not going straight....... This is also done with me NOT in the car....Thought it was strange but it works and it must be the way they do there chassis... :-k

Author:  ky mustang [ Thu Oct 01, 2009 9:46 pm ]
Post subject:  Re: Center of Gravity Height Again

The cog is fixed unless you move weight front to back or up and down on your chassis. If you move weight it changes where the COG is and the neutral line . The cog height would be like if you stood your car on its end and tried to balance it in a certain spot. We can't do that without damaging our car so that is where the math comes in to calculate it correctly from scales

A few weeks ago a friend of mine switched from aluminum heads to cast iron. The car slowed down from 5.60 to 5.80's but lifts the front end about double what it did. Its because the cog was raised by adding around 70 lbs. His ic stayed the same , but his a/s values changed.Power was decreased by a small amount. That is one thing I noticed recently that got me to looking at this differently.

Author:  BillyShope [ Fri Oct 02, 2009 6:08 am ]
Post subject:  Re: Center of Gravity Height Again

Beretta wrote:
I have been reading this all along and I just need some pictures along with it to help me see what you guys are talking about "lifting up the back" ....That spread sheet is not showing me anything...... ](*,) #-o

Oh and I have a set of scales..... ;-)

Take a look at the explanation above the spreadsheet on page 31. I don't know where you got the "lifting up the back" quote, but that would describe what you're doing as you set the car on its "nose" by "lifting up the back" of the car. This is usually done with a jack located at the center of the rear axle. Obviously, the scales are only under the front tires. Accuracy is increased as the angle of tilt is increased, which means...if you're using an ordinary floor jack...that you might want to do the lifting in stages. And this means that the whole procedure can be quite dangerous, so be very, VERY careful!
http://www.racetec.cc/shope

Author:  Beretta [ Fri Oct 02, 2009 8:06 am ]
Post subject:  Re: Center of Gravity Height Again

OK but how high should it be lifted???? Should it be done with me in the car???

Author:  BillyShope [ Fri Oct 02, 2009 5:41 pm ]
Post subject:  Re: Center of Gravity Height Again

Beretta wrote:
OK but how high should it be lifted???? Should it be done with me in the car???

How high? Well, if you're careful with your measurements, 30 degrees should be sufficient. That doesn't sound like much, but, when you see the car in that position, it's kinda scary. For me, anyway.

When you're scaling the car on the shop floor...to determine the fore and aft location of the center of gravity..., you might as well sit in the car. It's not necessary, however, for you to be in the car when it's in the tilted position. Before the car is tilted, get a vertical measurement from the shop floor to your belly button as you sit in the car. Then, suppose you weigh 200 pounds, the car weighs 3000 pounds, and the tilt test yields a center of gravity height of 20 inches. The center of gravity...with you in the car...would be that belly button measurement times 200 plus 20 times 3000, the whole thing divided by 3200.
http://www.racetec.cc/shope

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