High centre of gravity vs low centre of gravity - Page 4 - AUSJEEPOFFROAD.COM Jeep News Australia and New Zealand

4WD.COM
Find out how to advertise on Ausjeep?

Go Back   AUSJEEPOFFROAD.COM Jeep News Australia and New Zealand > GENERAL > Hot Topic of week


Portal Register Forums Trading Your Jeep New Garage Mark All Read

Post New Thread  Reply
 
Thread Tools Search this Thread
  #28  
Old 08-12-2012
SeaComms's Avatar
SeaComms  SeaComms is offline
MonsterMoose
 
Join Date: Jun 2010
Location: Noosa QLD.
Age: 53
Posts: 8,108
What Jeep do I drive?: JK
Likes: 1,282
Liked 753 Times in 425 Posts
Check out my Ride(s)
Default

Here's my 2c with some ideas to procrastinate on.

When referring to COG, it really has no relevance unless comparing two identical track/wheel base vehicles or you own vehicle in a before after lift scenario. If you increase the height of COG above ground of your vehicle, you will reduce stability, which increase the ease of which it will tip over. Now increase the wheel track and you have decreases the effect of the COG raise on a side to side basis, but not on an end over end basis.

To work it out you are looking at triangular calculations. First you need to know what your current COG is - something that most will never know anyway, so sort of makes any calculations almost impossible anyway, so we progress on theory alone with no real numbers! (racing teams often need this information and it can be calculated by placing scales under all 4 wheels, raise the scales on side to tip the vehicle and now look at the shift in weight on the scales. This change in weight along with the angle can be used to calculate current COG).

If you picture your vehicle from the side or behind, and draw a line from the COG point to the road where the wheels touch and measure the angle of these lines at the COG point. If this angle decreases (ie by lifting the vehicle/ raising COG or by reducing wheel track / wheel base) then this will reduce stability. Not a difficult concept. It should be noted that like the laws on lifting a vehicle, there are also laws on reducing wheel track - in fact you are not allowed to reduce the wheel track at all without Engineering approval due to the reduction in vehicle stability - not that many people would do this anyway.

What is required to negate a lift (increase of COG) affecting the stability? Looking back at the imaginary triangle from before we need to keep the angle at the top the same, so lifting this point will require spreading the wheels out both to the sides and the ends (wheel base increase and wheel track increase). The ratio of lift to required track increase to keep stability the same changes depending on what the COG starting point compared to wheel track was. This is why I mentioned before without knowing what your COG is to start with makes the calculations impossible. Its not as simple as lifting 2in requires 2in wheel track increase to keep stability the same (although this is actually true if your COG height above ground happens to start at exactly half your wheel track!)

However, what is not as easy to work out is what effect any of this has in the real world on stability of your particular vehicle. A lot will depend on how close you as an individual push your vehicle to the limits of its stability. If you never get within 20 of the tipover angle of your vehicle, then lifting the COG will mean you no longer get within say 15 of the tip over angle, so no real change in capabilities of your vehicle in your hands. If you are an extreme offroader or drive really hard round roundabouts/corner and consistently run your vehicle right at its limits of tipping over, lifting the COG will most likely find you rolling onto your side or roof if you continue to drive the same way.

Now of course that is presuming that the lift you just put in has identical spring rates, because if you have stronger springs then you won't lean as much on an off camber run or when hammering it around a corner, so you would be less likely to tip than if you were running softer springs. Another reason for one of the lift regulations - the one that states the any replacement springs must be as stiff or stiffer than the stock ones.

So in all there is a lot to go into calculations, much more complicated than possible for most, and this is one of the main reason for legal lift limits without engineering, as the engineer will look at this increase in onroad rollover potential as part of the approval. Off road effects are generally of no interest to the Engineer.

So, clear as mud
__________________
Cheers, Dave :)


2010 JK now replaced with 2015 Granite Crystal KL Trailhawk
Over 5'000 Club

Last edited by SeaComms; 08-12-2012 at 10:32 AM.
  #29  
Old 08-12-2012
Wooders's Avatar
Wooders  Wooders is offline
Time to tinker
 
Join Date: Jul 2002
Location: www.wooders.com.au
Posts: 10,788
What Jeep do I drive?: CJ
Likes: 134
Liked 447 Times in 232 Posts
Default

Not bad seacomms.
Only thing you haven't covered is changing the weight/location.
Eg:
Replacing the diffs with heavier ones, even without changing the suspension height will in effect lower the COG point. Even simply packing stuff in the cabin compared to on the roof.

Oh yeah formulas:
http://www.longacreracing.com/articles/art.asp?ARTID=22
Sponsored Posts
  #30  
Old 08-12-2012
Electric Monk  Electric Monk is offline
Established Member
 
Join Date: Nov 2011
Location: Sydney
Posts: 105
What Jeep do I drive?: TJ
Likes: 0
Liked 0 Times in 0 Posts
Default

Did you replace that woman's diffs Wooders?
__________________
2006 TJ
4.11, 32", 6 speed
  #31  
Old 08-12-2012
Gildo's Avatar
Gildo  Gildo is offline
Yeah I bought another one
 
Join Date: Oct 2002
Location: WWW Wheeling
Posts: 4,741
What Jeep do I drive?: XJ
Likes: 49
Liked 91 Times in 57 Posts
Check out my Ride(s)
Default

Why did I watch that video?
__________________
1x CJ8
1x YJ
1x MJ
1x XJ
1x Jeep trailers.
1x Empty Wallet.
Sponsored Posts
  #32  
Old 08-12-2012
BeatOffTheBush  BeatOffTheBush is offline
Senior Newbie
 
Join Date: Jul 2012
Posts: 75
What Jeep do I drive?: JK
Likes: 0
Liked 0 Times in 0 Posts
Default

Obviously LCOG. The only situation you would want higher lift would be to avoid belly scraping, a far lesser problem than overall stability with jeeps IMO.

They're one of the few vehicles which are very very easy to do a fender cut on, take advantage of that.
  #33  
Old 08-12-2012
SeaComms's Avatar
SeaComms  SeaComms is offline
MonsterMoose
 
Join Date: Jun 2010
Location: Noosa QLD.
Age: 53
Posts: 8,108
What Jeep do I drive?: JK
Likes: 1,282
Liked 753 Times in 425 Posts
Check out my Ride(s)
Default

Good point Wooders about the weights, never even though about that while writing it! Good link too, some nasty mathematics made all to easy by simply typing in you numbers. All we need now is some scales capable of supporting around 500 kg and we can work out!

But I guess the bottom line is keep the weight (as in lifts, packing the storage areas, roof racks and roof rack loads) as low as you can to keep it as stable as it can be.

Sent automatically by Tapatalk while I was busy working. Honest boss...
__________________
Cheers, Dave :)


2010 JK now replaced with 2015 Granite Crystal KL Trailhawk
Over 5'000 Club
Sponsored Posts
  #34  
Old 08-12-2012
Squall's Avatar
Squall  Squall is offline
AJOR Gold
 
Join Date: Aug 2008
Location: Sydney
Age: 35
Posts: 425
What Jeep do I drive?: TJ
Likes: 0
Liked 1 Time in 1 Post
Default

Ok my two cent worth

The lift will raise your COG and give you more articulation but leave your diffs at the same hight. But then you can increase your tyres With the extra space raising the diff height.

Cutting your guards will allow you to fill the larger space with bigger tyres and allow your COG to remain lower (the bulk of the Jeeps weight remains lower)

However the larger tyres (35+) mean you have to start looking at new diffs or at the very least re gearing your diffs. Not to mention other issues like steering issues and other upgrades.

I would say the best compromise is a two inch lift on 33s with lockers. Unless you are moving into comp spec stuff
__________________
J - just
E - empty
E - every
P - pocket

Why does my jeep want to bankrupt me?

Last edited by Squall; 10-12-2012 at 04:40 PM.
  #35  
Old 09-12-2012
Bogged  Bogged is offline
MudSplasher
 
Join Date: Feb 2003
Location: outside
Posts: 1,873
What Jeep do I drive?: CJ
Likes: 2
Liked 1 Time in 1 Post
Default

Tip from way back - Just fill your tyres with water.
  #36  
Old 10-12-2012
Richo's Avatar
Richo  Richo is offline
SwampDigger
 
Join Date: Nov 2004
Location: In the pony shed
Age: 15
Posts: 3,586
What Jeep do I drive?: TJ
Likes: 2
Liked 34 Times in 19 Posts
Default

Quote:
Originally Posted by Gildo View Post
Why did I watch that video?
Don't you mean why did you watch it four times Gildo?
__________________
Quote:
Originally Posted by Das_Colonel View Post
Yeah no need to be rude yeti, I'm not a total novice
Post New Thread  Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


» Advertisements_AS2


Powered by vBadvanced CMPS v3.2.3



All times are GMT +10. The time now is 09:57 AM.




AJOR does not vouch for or warrant the accuracy, completeness or usefulness of any message, and are not responsible for the contents of any message. The messages express the views of the author of the message, not necessarily the views of AJOR or any entity associated with AJOR, nor should any advice be substituted as technical advice replacing that of a mechanic. You agree, through your use of this service, that you will not use AJOR to post any material which is knowingly false and/or defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, religious, political or otherwise violative of any law. You agree not to post any copyrighted material unless the copyright is owned by you or by AJOR. The owner, administrators and moderators of AJOR reserve the right to delete any message or members for any or no reason whatsoever. You remain solely responsible for the content of your messages, and you agree to indemnify and hold harmless AJOR, the administrators, moderators, and their agents with respect to any claim based upon transmission of your message(s). The use of profile signatures to intentionally mislead or misdirect any member on this forum is not acceptable and may result in your account being suspended. Any trip that is organised through the AJOR forum is participated at your own risk. If you or your vehicle is damaged it is your responsibility, not that of the person that posted the thread, message or topic initiating the trip, nor the organisers of AJOR or moderators of any specific forum. This forum and associated website is the property of AJOR.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

AJOR 2002 - 2019 AUSJEEPOFFROAD.COM. All corporate trademarked names and logos are property of their respective owners. Ausjeepoffroad is in no way associated with DaimlerChrysler Corporation or Fiat Jeep.
www.ausjeep.com www.ausjeep.com.au www.midlifemate.com ausjeepforum.com Jeep Wrangler JL Australia release
vB Ad Management by =RedTyger=