TORSION BAR ADJUSTMENT

[mbaird]

I havent read every word of this thread so if it has already been discussed I apologize.

 

[72bluNblu]

I agree with BluNblu that the spring rate does not change.
However it is a lot like a rocker arm and I have to wonder what effect the angle of the adjusting bolt to the lever has on the force applied to the torsion bar ? The fact that the aduster anchor can pivot may nulify any effect ... hmmmm????

None. It has no effect at all.

The adjusting bolt does one thing, and one thing only. It sets the angle between the adjusting lever and the body of the LCA. Once the weight of the car is on the suspension, the LCA and the lever move as a single unit, twisting the hex end of the torsion bar. The angle of the bolt, or how far it’s threaded in or out of the adjuster has no effect on the spring rate at all.

 

[rapomnapalm]

IMHO. A broken torsion bar like that is a

manufacturs defect. It had to be twisted past its elastic limit to bend and would have to be brittle to snap. Just MHO but physics os physics

Problem isn't manufacturing flaws but the use of vice grips for removal of tortion bars. If you so much as nick the bar, when it goes under tortion it creates a sheer point.

 

[MopaR&D]

I agree with BluNblu that the spring rate does not change.
However it is a lot like a rocker arm and I have to wonder what effect the angle of the adjusting bolt to the lever has on the force applied to the torsion bar ? The fact that the aduster anchor can pivot may nulify any effect ... hmmmm????

My thought is, with the ride height cranked up to the max the LCA is at enough of an angle where more of the force from hitting a bump is transmitted along the arm into the chassis instead of twisting the torsion bar. In an impossible extreme case imagine the LCA is rotated so it points down at the ground; even if there is no torsion bar it would act as though there's no suspension at all. Same reason why lifted 4x4s ride worse, the farther away from parallel the leaf springs or suspension arms get from parallel to the ground the more force is transmitted into the chassis instead of the springs and shock absorbers.

 

[72bluNblu]

My thought is, with the ride height cranked up to the max the LCA is at enough of an angle where more of the force from hitting a bump is transmitted along the arm into the chassis instead of twisting the torsion bar. In an impossible extreme case imagine the LCA is rotated so it points down at the ground; even if there is no torsion bar it would act as though there's no suspension at all. Same reason why lifted 4x4s ride worse, the farther away from parallel the leaf springs or suspension arms get from parallel to the ground the more force is transmitted into the chassis instead of the springs and shock absorbers.

So we need to separate what we're talking about. The position of the adjusting bolt just changes the angle of the body of the LCA with respect to the hex socket for the torsion bar. That angle doesn't change anything ride related, because the force acting on the hex end is applied radially. The force is being applied at the ball joint end of the LCA.

Now, the ride height and the angle of the LCA at ride height does change the effective wheel rate. Because you're calculating the effective wheel rate based on the effective length of the LCA. So, if the LCA is at a 45° angle to the frame (up or down) the effective length of the LCA isn't its actual length, it's the length divided by √2. If the LCA is perpendicular to the frame rail then the effective length is equal to the actual length.

Thing is, the effective wheel rate is ALWAYS changing as the suspension travels up and down and there's nothing you can do about that. The other thing is, over the entire range the difference in effective rate is like less than 10 lb/in. And yeah, it's always and constantly changing as the LCA moves up and down within the range of travel. You can calculate the range based on the angles of the LCA when it's on the bump stops if you're looking to dial in a specific range, but all you can do to change that is change the torsion bar diameter, or reset the bump stop heights, but you wouldn't want to change those much unless it corresponds to the amount of travel you want.

 

[MopaR&D]

So we need to separate what we're talking about. The position of the adjusting bolt just changes the angle of the body of the LCA with respect to the hex socket for the torsion bar. That angle doesn't change anything ride related, because the force acting on the hex end is applied radially. The force is being applied at the ball joint end of the LCA.

Now, the ride height and the angle of the LCA at ride height does change the effective wheel rate. Because you're calculating the effective wheel rate based on the effective length of the LCA. So, if the LCA is at a 45° angle to the frame (up or down) the effective length of the LCA isn't its actual length, it's the length divided by √2. If the LCA is perpendicular to the frame rail then the effective length is equal to the actual length.

Thing is, the effective wheel rate is ALWAYS changing as the suspension travels up and down and there's nothing you can do about that. The other thing is, over the entire range the difference in effective rate is like less than 10 lb/in. And yeah, it's always and constantly changing as the LCA moves up and down within the range of travel. You can calculate the range based on the angles of the LCA when it's on the bump stops if you're looking to dial in a specific range, but all you can do to change that is change the torsion bar diameter, or reset the bump stop heights, but you wouldn't want to change those much unless it corresponds to the amount of travel you want.

I agree with all that you are saying with respect to the wheel rate, interface with torsion bar etc. What I'm talking about is the LCA's function as a suspension arm itself. It's the part that supports the weight of the car and absorbs the majority of impulses from bumps in the road. The farther from horizontal it gets, less of the motion from bumps gets transformed into a rotational force and more of it is transferred longitudinally along the arm and into the frame rail of the chassis.

 

[72bluNblu]

I agree with all that you are saying with respect to the wheel rate, interface with torsion bar etc. What I'm talking about is the LCA's function as a suspension arm itself. It's the part that supports the weight of the car and absorbs the majority of impulses from bumps in the road. The farther from horizontal it gets, less of the motion from bumps gets transformed into a rotational force and more of it is transferred longitudinally along the arm and into the frame rail of the chassis.

The LCA is just a lever. The forces are all acting on the wheel which is then carried through the spindle which is then carried by the ball joint. That force rotates the LCA and all of those forces are put into the torsion bar through the hex socket. Yeah sure, a small percentage of that force goes into the bushings, flex in the LCA, etc., but that's a small percentage of the total force.

With factory LCA's you can't even hang the LCA down at much more than a 45° angle before they hit the K frame, and the bump stops get involved before that. It's no where near steep enough to fundamentally eliminate the suspension, which is what you're talking about. If what you're saying was true, it would be a really ineffective suspension. And it's not.

Cars ride like crap when the suspension is raised all the way to the maximum because there's no (or not enough) extension travel, only compression. Slamming into the bump stop bottoms the suspension out and then ALL the force is translated into the frame. But it's not because of the angle of the LCA, it's because hard parts made contact and eliminated the travel of the suspension.