Why adjust torsion bars?

[MightyMouse]

Oh and forgot to answer your real question, a shorter control arm exerts less force on the bar than does a longer one therefore the bar / arm combination is effectively "stiffer" - that's why we use "breaker bars" on socket sets... same force, longer lever arm, more torque.

I have substantially longer arms on my IFS to get extra travel and the stock bars were a disaster. Fitting heavy duty aftermarket bars has just about brought it back to stock - a little softer but thats cool.

[-Scott-]

Oh and forgot to answer your real question, a shorter control arm exerts less force on the bar than does a longer one therefore the bar / arm combination is effectively "stiffer" - that's why we use "breaker bars" on socket sets... same force, longer lever arm, more torque.

I have substantially longer arms on my IFS to get extra travel and the stock bars were a disaster. Fitting heavy duty aftermarket bars has just about brought it back to stock - a little softer but thats cool.

Torque (Nm) and force (N) are two distinctly different entities, which you appear to use interchangeably. When you sort them out, I'd love to continue this discussion.

[Yom]

There's no need to be an eliteist so and so Scotty!

[MightyMouse]

Ok - I get the picture....

[NJV6]

Stick with it Scott
- too many people think winding up torsion bars increases tension. Providing the weight stays the same and the vehicle rises as you 'crank' then tension can't change! Unless you add more weight.


Most of the handling issues with raised IFS comes from having no down travel and this is also very important on road. When cornering with less than an inch from the bump stop (I have seen some with NO down travel) means as soon as you turn into a corner the wheel lifts off the ground.

I did a ball joint flip and cut bumpstops with low profile bolts, lifted it an inch and have more travel than standard and a better ride off road due to the extra travel.

[KiwiBacon]

Stick with it Scott
- too many people think winding up torsion bars increases tension. Providing the weight stays the same and the vehicle rises as you 'crank' then tension can't change! Unless you add more weight.

Yet it does change the link angles and steeper links impart more force vertically through the pivot.
Whether it's noticable or not depends on many many factors, one of the biggest being how sensitive you are to your vehicles behaviour.
Some people can't tell the diff between a flat tyre and one with 40psi in it.

So whether getting another 20mm of height results in a worse ride is something that could be discussed for eternity. But if you look at more extreme cases (compare a horizontal lever arm with one at 45 deg) it becomes quite obvious.

[NJV6]

Stick with it Scott
- too many people think winding up torsion bars increases tension. Providing the weight stays the same and the vehicle rises as you 'crank' then tension can't change! Unless you add more weight.

Yet it does change the link angles and steeper links impart more force vertically through the pivot.
Whether it's noticable or not depends on many many factors, one of the biggest being how sensitive you are to your vehicles behaviour.
Some people can't tell the diff between a flat tyre and one with 40psi in it.

So whether getting another 20mm of height results in a worse ride is something that could be discussed for eternity. But if you look at more extreme cases (compare a horizontal lever arm with one at 45 deg) it becomes quite obvious.

Yep cheers kiwi. I did have (excluding any differences in the angle of the arm acting on the torsion bar) written in the post then deleted it as I thought it'd complicate things!

[-Scott-]

OK, because I'm an engineer with few social graces, obsessive-compulsive disorder and no life I've been thinking about this some more.

MightyMouse raised a good point about the shorter effective arm length, and I've been trying to get my head around where forces are going.

When the suspension arm (i.e. lower control arm) is horizontal all vertical force is attempting to twist (applying torque to) the torsion bar.

When the suspension arm is cranked away from horizontal the vertical force can be separated into vectors which are perpendicular to the control arm, and parallel to it. The perpendicular component, trying to twist (torquing) the torsion bar, is reduced, and the parallel component is trying to compress the control arm, directing force into the chassis.

This was the bit I couldn't accept as being right, until I thought about the (physically impractical) ultimate "crank", where the suspension control arm is vertical. All vertical force is directed along the control arm, and no force is applied to twisting the torsion bar.

Looking at it this way, cranking torsion bars is introducing unintended sideloads into suspension components, but reducing the tension in the torsion bars. So, if you've got a second battery, steel bullbar and a winch, don't go for heavy duty torsion bars - just crank them some more!

There ya go! Lots of cr@p you didn't want to know, and probably didn't read anyway. I'll sleep well tonight, but it's probably thanks to all the beer.

[me3@neuralfibre.com]

OK, because I'm an engineer with few social graces, obsessive-compulsive disorder and no life I've been thinking about this some more.

MightyMouse raised a good point about the shorter effective arm length, and I've been trying to get my head around where forces are going.

When the suspension arm (i.e. lower control arm) is horizontal all vertical force is attempting to twist (applying torque to) the torsion bar.

When the suspension arm is cranked away from horizontal the vertical force can be separated into vectors which are perpendicular to the control arm, and parallel to it. The perpendicular component, trying to twist (torquing) the torsion bar, is reduced, and the parallel component is trying to compress the control arm, directing force into the chassis.

This was the bit I couldn't accept as being right, until I thought about the (physically impractical) ultimate "crank", where the suspension control arm is vertical. All vertical force is directed along the control arm, and no force is applied to twisting the torsion bar.

Looking at it this way, cranking torsion bars is introducing unintended sideloads into suspension components, but reducing the tension in the torsion bars. So, if you've got a second battery, steel bullbar and a winch, don't go for heavy duty torsion bars - just crank them some more! :P

There ya go! Lots of cr@p you didn't want to know, and probably didn't read anyway. I'll sleep well tonight, but it's probably thanks to all the beer. :D

Of course the above is based on static equilibrium. The "rate" of the spring (bar) is based on the need for dynamic behaviors.....