Vehicle COG comparison for longitudinal rollover

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
Sign up Log in
2 replies · 2K views
Raudi
Messages
1
Reaction score
0
Hi
I am trying to compare which of the (2) models has the greatest stability longitudinaly.
I have the COG height and longitudinal (axle split)
Model A has it COG closer to the centre of the axles (longitudinal - further from rear axle 1,487l) but sits much higher (2,537 above axle centre)
Model B has its COG closer to the rear axle (1,141) but sits much lower (1,745mm from axle centre)

Obviously there is a trade off going higher with the COG.

I believe that Model B has the greater all round stability by around 9%
The main factor that is trying to be quantified is which model is more likely to tip backwards.

X → Y ↑
Model A 1,487 2,537
Model B 1,141 1,745
 

Attachments

  • COG comparison.png
    COG comparison.png
    52.3 KB · Views: 627
Flipping forward or rearward is pitch stability, flipping on a sideslope would be lateral or roll stability. For your problem the tipping axis is the relationship between the axis of support (normal line from ground contact point of the closest wheel that goes through the wheel center) and line the connects the CG to the center of the closest tipping wheel, in your case the rear wheel. The vehicle flips when the CG moves outside the axis of support of that wheel based on the slope of the ground and acceleration. Statically, the free body diagram is a sum of the moments about that rear wheel, so the worst design occurs when the angle formed between the wheel center and CG, and horizontal - you have the x and y, so you have the angles are A - 59.6 and B - 56.8, so B is a lower angle and thus better. Don't forget to taking into account the maximum ground slope you can accommodate with a CG so close to a wheel. not sure where you got 9%?

If you need a diagram let me know...

You will also want the lateral static stability factor calculation. This calculation is used in the auto, ATV, and off-highway industries and is government metric. It takes into account suspension movement during the roll by physical testing on a tilt table.
Lateral the basic calculation is simple. static stability factor = T / 2* h (T is track width). (h is center of gravity height) for lateral assuming the cg is in the center.