Thread: sway bars and corrugations

Originally Posted by Jode

We were driving the (now sold) V8 110 on a heavily corrugated, flat road years back, travelling around 85km/hr, and suddenly found the rear trying to overtake the front. Fortunately no on-coming traffic so we just gently braked and stopped on the other side of the road .

We were running with 130 helper springs in the rear plus a rear anti-sway bar (came standard with none - we added the rear after a friend's fatal roll-over). I put the problem down to excessive speed for the conditions, and running with an open central diff. I think the speed was the primary cause.

Let's see if I've got some of this swaybar principal right?
On corrugations, where both wheels on an axle strike the bumps at the same time, a sway bar would make no difference to spring rates. On single wheel bumps, with a stiff sway bar, the spring rate for a single wheel could be doubled, because the sway bar would tend to compress the spring on the opposite wheel to the one striking the bump? Would the damper of the wheel striking the bump be capable of controlling the rebound force of double the spring rate? And would the spring on the opposite wheel be at a less than ideal rate if it strikes a bump before it has time to extend to normal ride height?
Bill.

Originally Posted by wagoo

On single wheel bumps, with a stiff sway bar, the spring rate for a single wheel could be doubled, because the sway bar would tend to compress the spring on the opposite wheel to the one striking the bump?
Bill.

Even a stiff sway bar would transmit only part of the force across to the other side. A completely rigid one might do what you describe.

Originally Posted by wagoo

Let's see if I've got some of this swaybar principal right?
On corrugations, where both wheels on an axle strike the bumps at the same time, a sway bar would make no difference to spring rates. On single wheel bumps, with a stiff sway bar, the spring rate for a single wheel could be doubled, because the sway bar would tend to compress the spring on the opposite wheel to the one striking the bump? Would the damper of the wheel striking the bump be capable of controlling the rebound force of double the spring rate? And would the spring on the opposite wheel be at a less than ideal rate if it strikes a bump before it has time to extend to normal ride height?
Bill.

That's right Bill. Also adding sway stiffness to the rear increases over-steer. Adding a sway bar to the rear only is something you never want to do on a landrover, it'll make it tail-happy.

The combination above of extra rear helper springs (already increasing roll stiffness) and an added rear sway bar is a setup I would never run. I am not surprised it tried to turn around, I am only surprised you didn't find this more often.
Feel free to run a front-only sway bar, but never a rear-only. There are very good reasons standard vehicles never ever come with a rear only sway bar.
It's always none, front only or front and rear. In that order. When they added sway bars to landrovers from the factory, the front was a monster and the rear very light. This was necessary to keep them pointing forwards when traction limits are reached.

Originally Posted by vnx205

Even a stiff sway bar would transmit only part of the force across to the other side. A completely rigid one might do what you describe.

The D flex sway bar, made from a half shaft is fairly stiff .
Bill.

Originally Posted by Dougal

That's right Bill. Also adding sway stiffness to the rear increases over-steer. Adding a sway bar to the rear only is something you never want to do on a landrover, it'll make it tail-happy.

The combination above of extra rear helper springs (already increasing roll stiffness) and an added rear sway bar is a setup I would never run. I am not surprised it tried to turn around, I am only surprised you didn't find this more often.
Feel free to run a front-only sway bar, but never a rear-only. There are very good reasons standard vehicles never ever come with a rear only sway bar.
It's always none, front only or front and rear. In that order. When they added sway bars to landrovers from the factory, the front was a monster and the rear very light. This was necessary to keep them pointing forwards when traction limits are reached.

I probably find the opposite - front wheel drive, rear sway bar, rear wheel drive, front sway bar. Constant 4WD probably doesn't make a hell of a difference, but if I recall correctly a rear is recommended. I have front and rear sway bars on my Defender. X-deflex on the back. One of the most significant problems with corrugations and vehicles swapping ends is axle steer from the front or rear, when either end suspension doesn't rebound and you end up heading off in the opposite direction to the side your suspension is compressed. The X-deflex does a good job of reducing axle steer by limiting suspension travel across the axle. I have been caught day dreaming and going too fast on the GCR and hit corrugations on the left side, ended up shistting myself and all over the road, then remembered I hadn't re-engaged the X-deflex. Totally different car from then on.

My front bar is a custom job, 28mm bar, longer arms and mounted back near the cross member to allow for prop shaft clearance. Probably as efficient as a standard bar and doesn't lift wheels as bad as I thought it would. Certainly makes a noticeable difference on the black top on roundabouts etc, but I would like disconnects for the bush.

Rick

Originally Posted by Dougal

Feel free to run a front-only sway bar, but never a rear-only. There are very good reasons standard vehicles never ever come with a rear only sway bar.
It's always none, front only or front and rear. In that order. When they added sway bars to landrovers from the factory, the front was a monster and the rear very light. This was necessary to keep them pointing forwards when traction limits are reached.

When they added a sway bar to my One Ten in the factory, it was in the rear, and only the rear. So, um, yeah, apparently at least one factory put them on the wrong end...

Disregarding that minor note, is there a link between sway bars being a good idea in the front and progressive rate springs being a bad idea in the front? (Or did I just make up the progressive front bad idea up?)

I can only go on what I've driven and thats a 110 wagon without sway bars and many different combinations of springs and shocks and a 110 wagon with sway bars running standard springs and shocks,save your money changing the suspension and buy a long range tank instead. Pat

Originally Posted by bushrover

I probably find the opposite - front wheel drive, rear sway bar, rear wheel drive, front sway bar.

Oversteer/understeer and roll-stiffness tuning isn't greatly affected by which wheels are driving, because the biggest problem is when they aren't driving.

I have never seen a front wheeldrive car (or any factory car) with only a rear swaybar. The ones I have owned only had front swaybars or both.

Originally Posted by Isuzutoo-eh

When they added a sway bar to my One Ten in the factory, it was in the rear, and only the rear. So, um, yeah, apparently at least one factory put them on the wrong end...

That is very strange. Does it have the front sway-bar brackets? The drop brackets on the front chassis and the mounts on the front axle casing? You've owned this vehicle from new?

Originally Posted by Isuzutoo-eh

Disregarding that minor note, is there a link between sway bars being a good idea in the front and progressive rate springs being a bad idea in the front? (Or did I just make up the progressive front bad idea up?)

Most vehicles run linear rates up front because the loading doesn't change as radically as it does in the back. Nothing to stop you running progressives in the front, but you need a lot of articulation or body-roll before they'll make much difference.