Patrol Pics



Anti-sway bars.

Anti-sway bars.

Postby Peter Connan » 24 Mar 2016 10:11

Following on from another discussion, here is some info on what the anti-sway bar contributes in terms of preventing a vehicle from rolling.

In order to accurately determine the true effect, one would have to accurately determine the centre of gravity. This is an almost impossible task, so I compromised as follows:
Nissan advertise a rollover angle of 48 degrees. Nowhere do they say whether this is measured on the ground or on the body though. So I took my chassis and suspension model and tilted it to 48 degrees, with suspension level. I then drew a vertical line from about 1/3rd the tire contact patch. Where this crosses the vehicle centre line should be close to the centre of gravity. I then added a ball to my model in this spot.

With the ground at 48 degrees, it looks like this:

Rolangle1.jpg
Rolangle1.jpg (253.12 KiB) Viewed 957 times
Mag ons ons kenniskry met lekkerkry aanhoukry.
User avatar
Peter Connan
Moderator
Patrolman 1000+
Patrolman 1000+
 
Posts: 4540
Joined: 10 Sep 2010 07:21
Location: Kempton Park
Has thanked: 112 times
Been thanked: 181 times
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.2SGL
Home Language: Afrikaans

Re: Anti-sway bars.

Postby Peter Connan » 24 Mar 2016 10:14

Next I tilted the suspension by 9 degrees. This is approximately the maximum a standard front suspension would allow.

I then drew a line from my contact patch to the centre of gravity, and rotated the whole lot until this line was vertical.
The result looks like this:

Rolangle2.jpg
Rolangle2.jpg (255.07 KiB) Viewed 956 times


The exact angle of the ground is less than 0.5 degrees less, although the body angle is now 57 degrees.
Mag ons ons kenniskry met lekkerkry aanhoukry.
User avatar
Peter Connan
Moderator
Patrolman 1000+
Patrolman 1000+
 
Posts: 4540
Joined: 10 Sep 2010 07:21
Location: Kempton Park
Has thanked: 112 times
Been thanked: 181 times
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.2SGL
Home Language: Afrikaans

Re: Anti-sway bars.

Postby Peter Connan » 24 Mar 2016 10:19

To take this a step further, let's see what adding a load to the roof will do. I added 500kg at a height of 2150mm (ie approximately 150mm above my roofrack), and calculated the change in the position of the centre of gravity. The calculation assumes a vehicle weight of 2000kg. The higher the vehicle weight, the less the CG would change.

With the suspension level, that gives me a rollover angle of 39 degrees:

Rolangle3.jpg
Rolangle3.jpg (254.09 KiB) Viewed 955 times


And with the suspension again tilted by 9 degrees, I get 37.2 degrees on the ground or 46.2 degrees of body angle:

Rolangle4.jpg
Rolangle4.jpg (255.49 KiB) Viewed 955 times
Mag ons ons kenniskry met lekkerkry aanhoukry.
User avatar
Peter Connan
Moderator
Patrolman 1000+
Patrolman 1000+
 
Posts: 4540
Joined: 10 Sep 2010 07:21
Location: Kempton Park
Has thanked: 112 times
Been thanked: 181 times
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.2SGL
Home Language: Afrikaans

Re: Anti-sway bars.

Postby Peter Connan » 24 Mar 2016 10:23

The above in my opinion proves that the sway bars have very little effect on when your car will roll, either due to side-slopes or due to evasive manuevres on the road. Obviously the calculations are not 100% accurate, and vehicle mods (lift kits and added weight) will play a role.

However, the worst-case change recorded here is 1.8 degrees between a vehicle that is totally resistant to roll (obviously not true) and a vehicle that is rolled as far as the suspension will go (also fairly unlikely).

Obviously, it will feel different, but that is just perception.
Mag ons ons kenniskry met lekkerkry aanhoukry.
User avatar
Peter Connan
Moderator
Patrolman 1000+
Patrolman 1000+
 
Posts: 4540
Joined: 10 Sep 2010 07:21
Location: Kempton Park
Has thanked: 112 times
Been thanked: 181 times
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.2SGL
Home Language: Afrikaans

Re: Anti-sway bars.

Postby Clem » 24 Mar 2016 11:50

You don't think that the bars help prevent an oscillation effect?
Clem
Patrolman
Patrolman
 
Posts: 692
Joined: 19 Jun 2013 15:16
Has thanked: 29 times
Been thanked: 8 times
Full Name: Clem Daniel
Nickname: Clem
Home Town: Johannesburg
Current 4x4: Patrol 4.8
Home Language: English

Re: Anti-sway bars.

Postby Peter Connan » 24 Mar 2016 12:06

Clem, these bars are in effect springs, and thus would tend to either exacerbate or keep oscillations going. Stopping that is the shock absorber's job.

Just to pull the dam from under the duck, I did a similar set of calculations as if the car were fitted with an un-locked X-link and the longest shocks that setup can use, IE 20 degrees of body roll.

Without load, that gives a ground angle of 43.9 degrees and a pants-wetting body angle of 63.9 degrees:

Rolangle5.jpg
Rolangle5.jpg (268.61 KiB) Viewed 940 times


With loaded roof rack, I get a ground angle of 32.2 degrees and a body angle of 52.2 degrees:

Rolangle6.jpg
Rolangle6.jpg (282.37 KiB) Viewed 940 times


So even with this extreme suspension movement, it still only reduced stability by 4-5 degrees.
Mag ons ons kenniskry met lekkerkry aanhoukry.
User avatar
Peter Connan
Moderator
Patrolman 1000+
Patrolman 1000+
 
Posts: 4540
Joined: 10 Sep 2010 07:21
Location: Kempton Park
Has thanked: 112 times
Been thanked: 181 times
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.2SGL
Home Language: Afrikaans

Re: Anti-sway bars.

Postby Clem » 24 Mar 2016 13:43

Peter Connan wrote:Clem, these bars are in effect springs, and thus would tend to either exacerbate or keep oscillations going. Stopping that is the shock absorber's job.


Well yes but more than that, by linking the two otherwise independent wheels and transferring force through a torsion bar setup, they tend to keep the wheel on the outside (that is to say on the side from which the body is rolling away) in greater/better contact with the road surface than it otherwise would have. In other words its not *just* a spring but a system for transferring downward force on the wheels from one side of the vehicle to the other - thus making the vehicle more stable than it otherwise would be and in that manner reducing oscillation forces. Also, the manner of setup can can change the degree of under- or over-steer; by setting them up to make the car under-steer (or under-steer more) it makes it safer handling for the average driver too (not everyone can safely handling a neutral or over-steering car).

Or am I missing something? I debate with you at my peril on anything mechanical.... :-)
Clem
Patrolman
Patrolman
 
Posts: 692
Joined: 19 Jun 2013 15:16
Has thanked: 29 times
Been thanked: 8 times
Full Name: Clem Daniel
Nickname: Clem
Home Town: Johannesburg
Current 4x4: Patrol 4.8
Home Language: English

Re: Anti-sway bars.

Postby Peter Connan » 24 Mar 2016 15:39

I don't think weight transfer has anything to do with suspension oscillation.

So let's look at weight transfer in more detail.

Exactly as you say, the torsion bar transfers weight from the wheel on the outside of the corner to the wheel on the inside. On cars with independent suspension, it plays a very important secondary role of trying to keep the wheels closer to square with the ground, but on live axles this obviously is not affected until a wheel lifts off the ground.

So as you corner, the inside wheel has less force pushing it into the ground, and the outer wheel more. As you make the roll resistance of a specific axle greater, this will happen more for the wheels on that axle, and less for the other axle/s.

What is important to realize is that handling balance only comes into play when one or more wheels start losing traction.

This will have the effect of reducing the cornering force reacted by the inside wheel of the high-resistance axle, and try to apply more to the outer wheel. However, this is already the most highly-loaded wheel, and it is thus starting to lose traction. On a live-axle 4x4 with high-sidewall tires, the tire is also probably rolling and deforming significantly at this point, further reducing traction. Therefore a higher rolling resistance usually results in less traction on that axle.

So the rule of thumb is, the axle with the highest resistance to roll is the one that loses traction first, and thus determines the handling balance. If the front axle loses grip first, the car will tend to understeer, or plough on straight.

Conversely, if the rear axle is the more highly resistant to roll, the car will tend to oversteer. IE the tail will start coming around and the car will either spin or drift sideways somewhat. This is when cars roll. Usually, one of the sliding wheels hit an obstruction and that throws the car over.

Thus if you remove only the front anti-sway bar, you are creating a situation in which the car will be more likely to roll in an accident.

However, it must be noted that it's not as simple in reality. There are many other factors that also contribute. The springs (strength, position and angle) as well as weight distribution, tires, suspension angles and many other factors play a role here.

Remember that SA GQ's came standard with an anti-sway bar only at the back, and the handling balance on those is still OK.

Also note that this is not the only factor affecting road safety. If the car understeers very badly, it may not be able to avoid hitting an object that a more neutrally-balanced car may easily be able to avoid.
Mag ons ons kenniskry met lekkerkry aanhoukry.
User avatar
Peter Connan
Moderator
Patrolman 1000+
Patrolman 1000+
 
Posts: 4540
Joined: 10 Sep 2010 07:21
Location: Kempton Park
Has thanked: 112 times
Been thanked: 181 times
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.2SGL
Home Language: Afrikaans

Re: Anti-sway bars.

Postby SJC » 30 Mar 2016 14:34

Found this in my 4500grx's owners manual....
Attachments
manual.jpeg
manual.jpeg (220.59 KiB) Viewed 863 times
User avatar
SJC
Patrolman 1000+
Patrolman 1000+
 
Posts: 2082
Joined: 23 Nov 2014 14:20
Has thanked: 43 times
Been thanked: 83 times
Full Name: SJC
Nickname: Fanus
Home Town: Lowveld
Current 4x4: 4.2TD Pickup & 4500 GRX
Home Language: Afrikaans

Re: Anti-sway bars.

Postby Peter Connan » 30 Mar 2016 17:47

Yes, there was a cable-release version for the gq too. But i have only seen it on swb wagons.
Mag ons ons kenniskry met lekkerkry aanhoukry.
User avatar
Peter Connan
Moderator
Patrolman 1000+
Patrolman 1000+
 
Posts: 4540
Joined: 10 Sep 2010 07:21
Location: Kempton Park
Has thanked: 112 times
Been thanked: 181 times
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.2SGL
Home Language: Afrikaans

Next

Return to 12. Suspension, Steering & Brakes

Who is online

Users browsing this forum: No registered users and 2 guests