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Old 04-19-2009, 06:16 PM   #1 (permalink)
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how do you find the center of gravity?

how do you find the actual center of gravity of your vehicle? so i can punch in the proper numbers in to the 4 link calc.

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Old 04-19-2009, 06:25 PM   #2 (permalink)
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Suspend it from three different points, drawing a plumb line across it from each attachment point. The area where all three lines intersect is the center of gravity.
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Old 04-19-2009, 09:19 PM   #3 (permalink)
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Meh...thats the exact way to do it but most of us just get it close. The top bolt of the tranny bell houseing is usually pretty accurate.

Put in 50" for COG and then put in 25". Pay attention to the summary. It doesnt affect much of anything. You obvioulsy want it low, but in terms of link calculators its means little.
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Old 04-19-2009, 09:42 PM   #4 (permalink)
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Suspend it from three different points, drawing a plumb line across it from each attachment point. The area where all three lines intersect is the center of gravity.
Can you elaborate on this please?

UH???? with out an accurate COG your anti squat numbers mean nothing! And last time I check most people run the 4-link calc to find their AS numbers more then anything!

Last edited by Toyota_Force; 04-19-2009 at 09:45 PM.
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Old 04-19-2009, 11:35 PM   #5 (permalink)
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Originally Posted by Toyota_Force View Post
UH???? with out an accurate COG your anti squat numbers mean nothing! And last time I check most people run the 4-link calc to find their AS numbers more then anything!
Not really. I will agree that an accurate COG is nessicary, however moving it 10", only affects AS by like 20%. Given that most builders have 3-4-5 mounting points for upper links........that 20% can be regained threw a mounting point. Like I said, Its important for the rig, but on the calculator....not so much.
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Old 04-20-2009, 12:06 AM   #6 (permalink)
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weigh the front of the vehicle when it's level, then weigh the rear of the vehicle. This will give you the total weight, and allow you to calculate "b" which is needed below.

now lift the rear up as high as you can, and record the rear weight again.

cg height = ((WF*l)-(W*b))/(W tan θ)

WF = weight of the front when elevated = total weight - the elevated rear weight
l = wheelbase
W = total weight
b = horizontal distance from cg to rear axle when level
θ = the angle you raised the rear of the vehicle

you will first need to calculate b which is .

WFL/W*l

where WFL = weight of the front when level
W = total weight
l = wheel base

the cg height given is the distance above the rear axle center line.

yes i got this from a book

Milliken, William F. Race car vehicle dynamics. Warrendale, PA, U.S.A: SAE International, 1995.

Last edited by dukegnarley; 04-20-2009 at 12:08 AM.
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Old 04-21-2009, 06:44 PM   #7 (permalink)
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Yes in some truck that have adjustability built in it's not a huge deal but for some people using pre-fabbed mounts with no adjustments it's a big deal! I guess it depends on the situation! But I know this one for sure has no adjustments and he needs to know so he can get it dialed in right hopefully the first time!


HOLY Hanna that's a huge equation! But ya that would work but not exactly easy to get! Any other ideas?
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