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View Full Version : Physics/ theories of Sway bar



keithlaw
03-23-2011, 10:47 PM
Hi everyone. I know a sway bar is a torsion bar that link up both sides of the suspension so that movement on one side is dependent on the movement of the other side. But people say that the end with a relatively stiffer sway bar will transfer weight quicker and break the traction sooner then the other end with a relatively softer sway bar. Here comes my question. As the bar only link the suspension together, one side moves up will force the other side to move up together so that roll will be reduced, I don't see anything to do with weight transfer quicker/ slower here.
If someone could provide some articles that talks about the physics behind the sway bar will be great.:msmile:

Thanks.

Garrett
03-29-2011, 05:37 AM
in for some info too

Zzyzx
03-29-2011, 09:24 AM
Dampers are the primary control regarding rate of weight transfer. However...

It could be said that although an anti-roll bar does not alter how quickly the suspension shifts weight, it does alter how quickly the weight at the tires contact patches change.

Bare with me here; In a suspension with no anti-roll bars the amount of weight the springs hold is equal to the weight @ the tires contact patches.
Example: An axle has 500 lbs applied to it equally (250 Left 250 Right). Enter a turn where 50% of the weight on that axle shifts and you have 125lbs on the left and 375 lbs on the right. These weights match the weight on the tires contact patch.

Add in an anti-roll bar, and for simplicity sake lets pretend that this anti-roll bars maximum force is 25 lbs. (I really don't want to have to spend the day doing math). Same instance, 50% of the weight is transferred in a turn. So, 125 lbs applied to the left spring & 375 Lbs applied to the Right spring. However now we have a torsion bar linking these two points, and as a torsion bar its going to try and resist twisting (limited to 25lbs in this instance). So, as the cars chassis rolls the torsion bar starts to resist twisting, causing an upwards thrust on the Left spring; as it follows the motion of the Right suspension. So now we have a 25 lb upwards thrust on the Right spring that happens to have a downward force of 125 lbs. So, we have to subtract that 25 lbs from the amount of weight actually making it to that sides contact patch & Add it to the contact patch of the Right. Giving us, 125 lbs applied to the left spring & 100 Lbs applied to the left tires contact patch and 375 lbs applied to the right spring with 400 lbs applied to the right tires contact patch.

So, we have not actually altered the rate weight gets transferred @ the springs; but since we have altered the amount of weight being applied to the tires contact patches over the same time period, we can say that we have altered the rate of weight transfer @ the tires contact patch.

incidentally with the 2nd instance we have also decreased the maximum amount of grip that end of the car can make because we have increased the amount of weight being transferred between the tires contact patches. So, that end of the car may feel like its reacting quicker... but its also making less grip overall.

codyep3
03-29-2011, 05:13 PM
i love your insight zzyzx, all of it thanks