Ok, I watched the Polaris IRS video on the Polaris web site again tonight. Look at the part where the quad goes over the rocks and you see the close up of the suspension action. The suspension has independent action. Yes I know it's IRS.

The way the sway bar is connected it seems to me that when one side compresses that the other side is forced to compress equally via the sway bar. That's not what you see in the video though. You see one side go up and the other side act independent, as it should.

The question is this: If the two sides are connected directly via the sway bar, then shouldn't both sides compress as one side compresses? Maybe the steel tube twists some. Educate me please.

 

Hey jefffoxsr. Usually a sway bar is able to twist between sides. Its intent is to keep the quad from leaning on a turn. It has the unfortunate side effect that it somewhat restricts articulation. That is why many riders buy sway bar disconnects. Jeepers do the same thing.
I hope this helps you
BryceGTX

 

With the sway bar connected you have about 4" of differenal movement ... under higher loads you could get more ... the sway bar has rubber bushings that "twist" with the vertical connecting rods, this "twist" adds load to the other side of the sway bar and stablize the IRS ... again connected you get about 4" of differenal movement.

With the sway bar disconnected you get the full movement without loading the other side of the IRS.

i hoped i help answer your question.

 

Thanks Chris.
I do have the sway bar disconnected like you do.

 

The vertical rods from the upper arms are connected to lever arms that connect to a square tube that is supported by plastic bushings inside the support tube. The square steel bar acts as a torsion rod type spring transfering the force to the other wheel. The more force applied across the wheels, the more the square rod twists. The rubber bushings act just like in cars, they allow the bolts in the upper A-arm and the levers to twist in the holes. They provide little or no spring type action.
I hope this clears things up for you.
BryceGTX

 

Bryce, you said it well. That's my understanding of the system also. Since both sides are connected as such, I wonder why compression on one side doesn't force equal compression on the other side.

 

The only way this could happen would is if the the square steel tube was not a torsion rod spring. If it was a non-spring rigid rod instead of a spring, it would do what you said. Instead one lever arm or side of the square rod twists up, the other lever arm or side of the square rod twists down by an exact equal amount. So some (not all) of the movement between the two sides causes the two lever arms to twist in opposite directions. The goal is to allow some of this force to be transmitted to the other side, but not all of it. If all of it is transmitted, the rear end would act like a straight axle.
I hope this helps
BryceGTX

 

Let me put this into numbers. Lets suppose that you put 50 pounds of force up through the right rear wheel (using a jack) to compress the suspension. Next put say 50 pounds on that side of the quad to keep the quad level. Lets suppose the 50 pounds causes the suspension to compress by 2 inches on the right side. The lever of the torsion bar on that side will move up by 2 inches (ignore any lever ratios). Now lets suppose the spring rate of the square tube is 10 pounds per inch of lever movement. Since the lever arm moves by 2 inches, it will attempt to transmit only 20 pounds of force to the other wheel (2 inches times 10 pounds/inch). However, this 20 pounds will not be enough to force the left suspension 2 inches as on the other side. Instead it only moves it about 0.8 inches. So the left side does go down slightly, but not nearly as much as the right.
I hope this clears things up.
BryceGTX

 

BryceGtx,
Thanks for the explanation. If I understand what you are saying, then the torsion bar has some twist to it and it won't direct 100% of the energy from one side to the other. Is that correct?

Have you seen the pics on Chris' page?

http://www.checca.net/atvswaybardisconnect.htm

It seems that for one side to compress it has to overcome some of the spring and shock pressure of the other side because the torsion bar connects both sides. Without the torsion bar connected the amount of pressure for each side to overcome is less, resulting in the dramatic articuation you see in Chris' pics.

 

You got it jefffoxsr. I saw Chris's pages from another thread; great pics. It is a good illustration of the effects of the sway bar disconnect. Now if you want to see exactly the opposite end of the spectrum look at my Trailblazer when one of the rear wheels goes over a big bump or goes in a hole. LOL, one of the other tires reaches for the sky. Now you can imagine a Sportsman with no spring in the sway bar!!
BryceGTX