Center of gravity thread

[06 H3]

Here is a thread to talk about the concerns of COG. Feel free to post up what you know and post up questions on what you want to learn and hopefully we can even get a chart going too.

 

[ReconH3]

This is a great thread that many people overlook. Most people don't understand that COG isn't only an issue that concerns roll overs. COG also affects traction greatly. For example: big heavy spare tires on rear rack cause you to lose traction on the front wheels on uphill climbs. Adding more stuff like fuel containers and hilifts only makes it worst. Adding the spare to a roof rack makes it worst when there is side to side movement because it amplifies the loss of traction on the opposite side. The ideal spot would be inside the vehicle, flat on the ground, right behind the driver and passenger. Most of the time, due to space constraints, that is not possible. Try to keep all cargo as low as possible and as close to the center of the vehicle as possible.


"Ex Umbris Venimus"

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[06 H3]

Thanks for the input recon. I know you would have good info on this. I sorta learned a bit late in the game but nothing is permanent. My issue is that I need the 2nd row so keeping everything down low can be tough but I will work on it

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[Flash]

Never really thought too much about it, other than seeing Manny (THCI magazine) in photos of rolling his H1 on a side hill traverse. My very limited offroad driving has been pretty much up or down hills. Noticed (by chance) that when I pack my tools and spare parts on the floor behind the driver and passenger seats (as opposed to the rear area) I get better traction going up hills. Also noticed that 4 passengers make all the gear go in the back and make finding good lines on rocky terrain more challenging as the vehicle is loaded differently than when driving solo or with just the Mrs.

Good thread idea. I look forward to learning much.

 

[ReconH3]

Thanks for the input recon. I know you would have good info on this. I sorta learned a bit late in the game but nothing is permanent. My issue is that I need the 2nd row so keeping everything down low can be tough but I will work on it

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I learned the hard way, but I am also aware of how people need to preserve all the seating. Everything in this life is about compromises. The idea is that you make your choices consciously knowing the effects it will have.


"Ex Umbris Venimus"

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[06 H3]

Everything in this life is about compromises. The idea is that you make your choices consciously knowing the effects it will have.


"Ex Umbris Venimus"

Sent from my iPhone

That applies to everyday life too!

I will try and put up some pics of when I had my door damage...I was leaning bad!! I dont think the rack will put me in a position bad enough to roll and I will be conscious of it.

A rollover is my biggest concern but that can happen on Low COG rigs if the driver is dumb enough. Its just that a roll over would leave me with a lot of work that I would have to do to bring it back to normal and even though it would be cheaper to start over again I dont think I could I am just a tad attached

Recon would one way to help on leaning is bringing the trackwidth out?

 

[LagunaH1]

Well, let me state the obvious: The H1's COG is low in relation to it's very wide width. I like that.

 

[06 H3]

Well, let me state the obvious: The H1's COG is low in relation to it's very wide width. I like that.

Yes I agree. That is why they can have little flex and not roll over. The new "cool" rig build up is full width axles so they are super wide and stable.

 

[kflips]

Do I recall a desired approach is to have front weight to rear weight within a 60-40 band ?? there are those stands that let you check the flex on your truck but not such an easy thing to calculate or test roll over against the manufacturers info -- Is there an easy way to test it

 

[Portager]

There are three components center of gravity the X or front to rear distance, Y or side to side distance and the Z or vertical distance.

With four scales on level ground you can determine X and Y but not Z. By making your measurements on a slope or raising one side or end or can determine the Z CG.

 

[06 H3]

Kflips, for you and mike steep climbs shouldn't be an issue. Longer wheelbases can help on steep climbs for stability. The downside is that in the rocks the longer wheelbase can get hung up easier

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[bebe]

I tried to get a hold of someone to get you weighed - seems they are all at SEMA in Vegas.

 

[06 H3]

Thanks for all the help bebe. They will all be back next week right?

 

[Ron B]

I believe a stock humvee will take 50+ degrees side slope. A year or so ago Zman on the HML put his 4dr hummer on a side tilt lift to see what it could handle -- I think the uphill tires started to lift at 43 degrees (42" tires and 6 inch body lift...so the truck was about 8" or 9" higher than stock). A stock hummer will do more but anything over 35 degrees is spooky and crossing 40 is serious butt pucker. There are some fun sideways spots on 2N17X, though I don't think they are more than 35 deg -- momentum will kill you when you are that sideways.

The reason I got an open top was because it has a bit lower center of gravity than the 4dr or wagon (300 to 500 lbs less of roof and glass). Rolling is my biggest concern. It's why I added to my roll cage and keep everything strapped down.

 

[06 H3]

Interesting Ron. Do you know where he went for that side tilt? That would be a good documentary thing to have on here along with some #s for the weight pads. Then we would have alot of info on cog. Btw what is trackwidth you have right now?

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[HUMMER INVESTMENTS]

We decided to pile up some dirt, and see if the H1 could make it across going over the side. Well my Pops was the one that drove it because i got a little freaked out. So i decided to get my phone, and when I used the angle measuerer, it said he was at 42 degrees. So with a little companction i think we got the hill down a bit and since i think weve gotten used to the tilt. Ill see if i can get a video of it soon after I get in my CB

 

[Ron B]

I went and searched for the thread about Zman's side tilt test I mentioned in my last post -- it was from '08 and I need to make some corrections -- tires lifted at 41 degrees (not 43) and it was a 3" body lift (not a 6"). So the truck was about 5" or 6" over stock (not 8" or 9").

here os a link to the thread:

http://www.hummernetworkforums.com/viewtopic.php?t=216246&postdays=0&postorder=asc&start=0

and a pic or two from the afore mentioned thread

 

[M22KLARS]

Aaaaaaaand... You're welcome. :hans:

 

[bebe]

Yes - SEMA ends on Friday

 

[bebe]

There are three components center of gravity the X or front to rear distance, Y or side to side distance and the Z or vertical distance.

With four scales on level ground you can determine X and Y but not Z. By making your measurements on a slope or raising one side or end or can determine the Z CG.

Actually you can, the digital scales ask for input of height, width and length, then with the weight it calculates COG.

My trucks COG is 31" (before I took the rack off. I'll measure it again this weekend with the rack off and see how much it decreases).

There are so many additional components to stability in relation to COG. Add force, speed, weight distribution (junk in your trunk) and it will change everything in an instant.

Tipping point is what most of us are concerned with, and what I mentioned above, it changes constantly. My point is COG is only a part of tipping point. So many trainings I've been to say you will never know your tipping point until you flop. (Trail wise that is). So if you can test your truck (using a forklift w/straps is another way) you can lift it till the straps pull.

But I have also seen a change in tipping point depending on the tire pressure and and the softness of a side wall. It can fold under and send you packing.

Then - you have to add motion to the equation. (force). Moving forward, backward, making a turn etc. Add: uneven terrain too - you can measure your COG but it all goes to hell when you are on big rocks. Knowing your vehicle (experience) is no replacement for a number.

See what I mean - COG is just a component of a flop in the making

 

[ReconH3]

Like Bebe explained, there are too many changing variables to try to put a scientific number to it. Driving your truck is what will give you a feel for it. Like anything you become good at, the more experience you accumulate, the better you become at gauging it.


"Ex Umbris Venimus"

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[ReconH3]

The one goal I had when I built my competition TJ, was the same principle I applied in my H3. I try to lighten everything I can from the frame up, and beef up everything I can from the frame down.

On my TJ I removed the roof and all glass. Including the windshield and replaced it with Speedglass. Speed glass is a special plexiglas that has the surface treated so it doesn't scratch. Made the axles heavier Dana 60/44. Heavier wheels: 36" Swamper TSL/SX on Champion beadlocks. Spare sits on the floor behind driver. The two huge marine winch batteries sit right behind the driver and copilot in the rear footwells. Even if my TJ is now 5" taller than factory, I actually have a lower center of gravity. The center of gravity is also more centered to the middle of the vehicle than if I had kept the spare in the rear rack.

On my H3 I removed the rear glass when we did the slant back conversion. Had I not done the slant back, I would have replaced the rear glass anyways with aluminum panels. One thing I plan to stil change, is the rear passenger doors glass with Speedglass. I also plan to put the spare inside the vehicle when I don't need it as my DD. The heavier axles and wheels, as well as the wider track width have also contributed to a much more balanced vehicle.

Those are the mods I did but may not be the appropriate ones for everyone. The requirements of each individual are always going to be different. Whatever you do, just be aware how it affects you and adjust your driving accordingly. Over time you will learn to "feel" your center of gravity. No gauges or science will ever make up for experience gained out on the trails.


"Ex Umbris Venimus"

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[Ron B]

as mentioned, it's good to know a ballpark that is "safe" for your truck -- momentum, upward/downward angles, which side of the ice chest your beer flops to are all considerations. I don't want anything above the roofline and try to keep the weight as low as possible.

The approx cg for a hummer wagon was discussed on the HML and is located above the rockers, but below and just behind the driver's ass. This was done on purpose by AM General so butt-pucker has little affect on side-slope ability.

The humvee/hummer/h1's numbers of 40% and 60% abilities are not rollover points, they are angles that you can be at all day without starving critical components of oil. As mentioned earlier a stock h1 will be fine up to 45+ degrees while static...moving/bumping around on a trail will drastically change this number. I don't like to go over 40 if I can help it. Did 45 once -- freaky. I felt better after deflating my uphill bags.

Get an inclinometer and learn a ballpark. You will sleep better.

 

[deserth3]

Oh Poop.... Just close your eyes and go for it.:hans:

If you offroad eventually something is going to happen. And there will be some idiot critic saying what an idiot you are.

 

[06 H3]

Desert I will try that and see where it gets me

There are just so many variables! One thing that you three,(bebe recon and ronb) have that I dont is experience so I guess time will help with that, trail time that is.

Ron: I have an inclinometer and its helpful, I think bebe once said start getting scared at around 38. lol

Recon:One of the toughest rigs to build is a daily driver. Comp rigs can be torn down and put stuff wherever, it really makes life easier. DD's need to have space for multiple passengers, trunk space for the crap we need and all the other stuff that can hinder the COG. Btw where do you keep your hi lift? I doubt you need one but there is no way I can store my 60" hi lift inside, so thats why its weight up top on the rack.

Also to recon: what is your trackwidth? do run the same full widths that the ORE JK's run. They are around 88in wide

This is a question to all. Eventually I will do shocks, along with many other variables even these will have a role too? Lets say you have a shock with 12" of travel wouldn't you have less body roll if it was divided up 6/6 or 5/7 instead of 11in of downtravel and 1 in of up travel? I know a guy who runs his shocks like 11/1 and once he has reached all the up travel wouldnt that start giving body roll and affecting the COG?

Also lifting IFS is hurting your COG unless the trackwidth is brought out or flex is gained?