Member Since: 14 Nov 2019
Location: Usk
Posts: 412
Where is your COG?
COG = Centre of Gravity
Probably of no interest to the majority of owners, but I had reason to consider it. I installed a 4 tonne two post lift in the workshop, specifically to lift 4x4's. Given that my Disco 3 weighs more than 2.5t I thought it would be a good idea to check the front to rear balance point (COG) This means no tilting force on the pillars. There are probably charts for this but I didn't find any useful search results.
The process and calculation is fairly simple. Beam scales to weigh front axle and rear axle separately. Here are the results,
car chassis body
kg kg kg
front axle 1360 917 443
rear axle 1220 374 746
total 2580 1291 1289
wheelbase 2885mm
a = distance from front hub centre to COG
a = (r / t) * w
a = 1252mm a few cm forwards of the door pillars
I found an online calculator to show the vertical COG if you enter a slope incline. Might be useful for serious offroaders brave enough to test the limits.
12th Apr 2020 9:39 pm
highlands
Member Since: 11 Jan 2010
Location: NW Highlands
Posts: 5098
Was that with a full tank?
I think there was a YouTube video of someone removing the engine from a car on a 2-post lift and the car falling backwards off the lift.Black 05 TDV6 HSE Auto
Grey 05 TDV6 HSE Auto (Gone)
54 TDV6 SE Man (killed by me )
12th Apr 2020 10:02 pm
waterbuoy
Member Since: 26 Oct 2013
Location: Argyll
Posts: 2881
Mine is about 8" above the waistline Currently 2009 Disco 3 SE, 2013 MY D4 HSE and 2016 D4 SE
Previously:
TD5 Defender 110 CSW (230k miles)
300TDi Disco 1 (289k)
4 RR Classics (300-350k each, 2 manual, 2 auto)
110 V8 CSW (220k)
S3 109 hi cap pickup (ex RN)
S2A 88 Safari SW with lpg conversion (bloody lethal)
12th Apr 2020 10:15 pm
Sidestick
Member Since: 22 Apr 2012
Location: Rome
Posts: 2301
and mine is over 2800kg - Easy-Lift suspension module 4.0
- GoodWinch 9500 lb
- Full underbody protections
- Tree/Rock sidebars
- Prospeed roofrack & ladder
- Compressor guard
- Raised Air Intake
- Driving lights (2+4)
- 50 mm Waffle boards
- Altox Heater control
- Overland Rooftop Tent
- Rear seats entertainment
- Front & Rear camera
- GVIF
- Removable tow bar
- Cubby box fridge
- BFG KO2 265/65R17
- iidTool BT
13th Apr 2020 10:44 am
DSL Keeper of the wheelie bin
Member Since: 11 May 2006
Location: Off again! :-)
Posts: 72907
highlands wrote:
Was that with a full tank?
I think there was a YouTube video of someone removing the engine from a car on a 2-post lift and the car falling backwards off the lift.
Which is a good reminder that the CoG moves backwards once the big lump in the front is lifted out.
Oh, and I take absolutely no responsibility if anything I say in this thread is wrong and leads to damage to car or owner, whether minor, major or total.
13th Apr 2020 10:49 am
motorworks
Member Since: 14 Nov 2019
Location: Usk
Posts: 412
A full tank of fuel adds weight, but tank is under floor behind the driver so not of great significance to COG.
I am apprehensive working under the car at full height. Total weight is well within capacity, but slip or movement on one of the lift points would be dangerous or worse. Removal of engine or back axle could make a significant difference, as could any similar weight left in the load space.
There are a few Youtube examples of lift disasters, which seem to happen suddenly with no warning. A Chinese mechanic died in a futile attempt to stop a Rolls Royce slipping off a lift. I believe they are 3t or more.
I have since checked COG on several other vehicles including small hatchback, family estate and vans. The distance from lift to hub centre is in a surprisingly small range.
13th Apr 2020 11:49 am
Discoveringcomfort
Member Since: 16 Sep 2015
Location: Berkshire
Posts: 637
I replaced my rear diff on a two post lift without issue.
True it helped that the car was positioned by a garage manager before I did the work.
During the process both rear wheels and the diff were removed so quite a bit of weight change.
Edited to add pic.
Series 1 V8
Series 2 Hibrid V8
Discovery 3 HSE V8
Last edited by Discoveringcomfort on 15th Apr 2020 5:33 pm. Edited 1 time in total
13th Apr 2020 3:53 pm
Globetrotter448
Member Since: 21 Mar 2017
Location: Londonderry NSW
Posts: 1791
There again, the front arms are short and the rear arms are long
15th Apr 2020 9:52 am
motorworks
Member Since: 14 Nov 2019
Location: Usk
Posts: 412
I weighed a D3 TDV6 (2.7) engine with auto gearbox. Less than I expected, but still a heavy lump at 300kg. Later I will recalculate COG, with this weight removed.Chris
3rd May 2020 5:09 pm
Globetrotter448
Member Since: 21 Mar 2017
Location: Londonderry NSW
Posts: 1791
COG does come into it, but it relates more to where the arm are positioned.
4th May 2020 12:32 am
motorworks
Member Since: 14 Nov 2019
Location: Usk
Posts: 412
"COG does come into it, but it relates more to where the arm are positioned."
You mean safe lifting relies on arms positioned with distance from COG, to minimise the possibility of tipping or movement?
Removing engine and gearbox (300kg) pushes COG from 152cm out to 179cm, distance from front hub centre. This point is a few mm rear of the door gap.
Another observation. Body COG is at 180cm, but it is not possible to position the arms for a balanced lift. So there is significantly more weight on the rear arms.Chris
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