Center of Gravity Anyone?¿

[IZwack]

Center of Gravity Anyone ? ¿

No idea where this type of question belongs but since I'm using it to calculate a 3-link front suspension (anti-dive numbers), I thought I'd throw it in here.

Anyways, has anyone done any calculations and figured out where the center of gravity (COG) is on lets say a stock explorer?

I've read on pirate that you could assume the top bolt on the bellhousing but I just want to ask anyone on this board before I make the assumption.

 

[IZwack]

bumpity!

 

[FROADER]

I think it belongs in this forum so here you go. Haven't measured it by the way so good luck.

 

[IZwack]

I think it belongs in this forum so here you go

Ahh true. Thanks for the move!

 

[Chris97Exploder]

Do you need the (x,y) CG of the vehicle or just the x position. The x can be found by balancing the vehicle. But the y would be more difficult/near impossible. Of course it will all be an approximation because you'll never be able to perfectly balance it.

 

[IZwack]

unfortunately, its the Y position (or height) that I need in order to calculate the anti-dive. The Y position can also be found by balancing the vehicle but twice - one with it level on the ground and the next with one end at least 2 feet higher than the other (as if it were on a ramp). the difference between the two weights on one end can be used to triangulate the location of the CoG. but, i dont have access to a scale that can read thousands of pounds.

Anti-Dive % = (COG Height * IC Position)/(Wheelbase*IC Height)

 

[Bronco638]

... but, i dont have access to a scale that can read thousands of pounds...

Did you try a local truck stop? They always seem to have those "CAT" scales advertised on the highway signs.

 

[MrShorty]

Interesting question. I recall thinking quite a bit about this a while back (more along the lines of "when will it roll over sideways"). Here's my "seat of the pants" estimate:

Brake test from safety inspection shows 2300 lbs over front axle, 2000 lbs over back, so my Explorer is fairly well balanced front to back. COG would be a little forward of the middle.
For all practical purposes, vehicle should be balanced left to right. Explorer has gas tank on the driver's side which will shift the COG a little to that side, but 20 gallons of gas is only ~150 lbs, so it won't shift it a lot.
Didn't have any idea on the weight of the glass and roof, but I figured that the roof and glass added a relatively small amount to the weight (10% or 400-500 lbs???). The bulk of the weight would be between the frame and the top of the hood. So I measured between the bottom of the glass and just below the bottom of the door, and said that the COG would be a little above the midpoint.
Can't remember for sure, but it seems like my analysis put the COG somewhere in between the seat and the dash, maybe about where that ashtray/cigarette lighter sit.
I hadn't heard about the "top of the bellhousing" rule of thumb, but that's probably not too bad of a rule of thumb. My analysis would put the COG a little above and little behind the top of the bellhousing.

 

[rookieshooter]

unfortunately, its the Y position (or height) that I need in order to calculate the anti-dive. The Y position can also be found by balancing the vehicle but twice - one with it level on the ground and the next with one end at least 2 feet higher than the other (as if it were on a ramp). the difference between the two weights on one end can be used to triangulate the location of the CoG. but, i dont have access to a scale that can read thousands of pounds.

Anti-Dive % = (COG Height * IC Position)/(Wheelbase*IC Height)

I'm interested in this also. Are you saying that you need two sets of scales when doing the part with the rear up 2 feet higher. Could you do it with one truck scale with whole truck on scale. Then just front or back on scale but jacked up 2 foot? I would like to do this to my project truck. and then to a more or less stock B11. Glad you brought this up.

Just Googled it. It's fairly easy with something flat. They gave an example of a irregular shape of cardboard. Just hang with string at two different places and intersect lines. But something like a 3 diminsion truck. They lost me. But same concept. triangulation. They said that the exact COG is buried deep inside. OK but where.

 

[IZwack]

Thank you much MrShorty. Yeah my estimates are along the lines of what you said. I'm guessing its somewhere near the center console and probably near the floor somewhere.

The good thing is is that I only need one of the 3 domensions that locate the CoG - which is the dimension that says how high it is from the ground - but unfortunately, I don't have the proper tool (scale) to measure it.

I will probably just go with somewhere between floor board and the center console (since i have a 3" body lift) and error for lets say plus or minus 3 inches vertically. The fairly long and moderate wheelbase of the explorer will drown out the +-3 inches of error during calculation.

I'm interested in this also.

rookieshoooter >> no only one scale... but you can read the entire process here: http://www.jeepaholics.com/tech/cog

Hopefully the above website isn't the same one that confused you

.

 

[rookieshooter]

Thanks just marked it. If you get your COG found, like to hear where it is. As if it's lost. LOL

 

[IZwack]

If you get your COG found, like to hear where it is. As if it's lost. LOL

Hehe I doubt I'll be able to find it. I'm just going to make an estimate and take into consideration a boundary error during calculations of the anti-dive value (aiming for 75-80% anti-dive is probably good enough)