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Author Topic:   center of gravity???
jello
Dirt Roller

Total posts: 16
posted February 14, 2005 08:12 PM  
tried to figure the center of gravity by
using the formula in the tool box came up
with a center of gravity 60 inches back
from the front tire and 36 inches above the
ground. Does this sound normal or did I
mess something up. I thought I was gonna
have to build a taller garage when I tried
to jack that thing up so high LOL. I dont know what I was expecting, but the vertical
# seems high to me.

thanks for any help

Iowamod20
Dirt Full Roller

Total posts: 73
posted February 15, 2005 06:10 AM  
36" is way high. If this is a dirt modified, you can just assume 18.5" to 20" high for your cg and be pretty close on your calcs.

jelloatwork
Dirt Newbie

Total posts: 1
posted February 15, 2005 06:35 AM  
who knows what I did wrong, but thanks
for the info.

here is what I came up with. . .

wheelbase 108
weight 2350
adj. wheelbase 104.5
rear% 56
raised the car 24 inches
weight added to front wheels 184 lbs

anybody see where I fell off the wagon??

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted February 15, 2005 07:14 AM  
Make sure your wheelbase is actually 108.

Also at 108 raising 24", I come up with more like 105.3" adj wheelbase.


Generally I think you can consider the cam heigth roughly the height of the center of gravity. Then you can place ballast in the car based on that.

dluna
Dirt Freak

Total posts: 334
posted February 15, 2005 07:24 AM  
Ballast above CG = more body roll / side bite?

Opposite happens for ballast below CG?

Is this correct?

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted February 15, 2005 08:31 AM  
Actually ballast above roll center not necessarily center of gravity. Adding ballast anywhere above the roll center height will produce more transfer.

What I meant was you can aadd ballast around center of gravity and not affect the car as much as adding it above or below the center of gravity. If you have a car that handles really well but you just need to add ballast but dont want more roll, transfer or whatever then you should add it around the center of gravity height, that way it wont affect the car as much. Technically it will change some because you are still adding more weight above the roll center but i think you get the idea.

wfoondirt
Dirt Forum Champ
Total posts: 505
posted February 15, 2005 02:06 PM  
quote:
Adding ballast anywhere above the roll center height will produce more transfer.

Thats not always the case. Body roll is based on the length of the moment arm between the rc and the cg. The only way to increase it is to raise the cg, i.e. add weight above the cg, which in most every case is above the rc. If you add weight that is above the rc but below the cg you will actually lower the cg thus resulting in less body roll. Also roll center height (RCH) has no direct effect on total lateral weight transfer. Total lateral weight transfer is defined as:
Lateral Weight Transfer = Weight * CG Height / Wheel Track * g Force
Thus the RCH doesn't come into play directly.



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