so the torsion bar is twisting less thus feels "softer".

That part. Excuse the inaccurate terms I will surely use expressing my question.

The energy absorbed from slamming the pothole dissipates through the T-bar, the shock, tire etc. or in upward travel of the entire vehicle. Explain to me how it differs between my soft truck and Johns firm truck.

For simplicity, assume we are exactly over and under the stock setting by 10 degrees. (which we'll just assume is perfectly level)

Not asking for an accurate numerical value, beyond what is necessary for illustration. I think I am tracking now, but I need to understand this part for sure.

Thanks, enough for tonight. I'll try to get George to chime in tomorrow. Between the two of you, I'll get it solid. Before we proceed to T-bar preload. Which I suspect is going to be a tougher explain. Article opened up OK for George.

 

Try this. First let's all agree that the torsion bar twists directly in proportion to how far the lower A arm moves, so we can forget about the actual mechanics and only need to examine the movement of that A arm.
Here's a graphical diagram of the left lower A arm looking from the rear of the truck, the center of the circle represents the pivot at the crossmember, the circle itself the path the ball joint end travels. Again to simplify lets lock the frame a fixed height above the roadway. Also we will only look at what happens as we drive over a series of steps that are progressively increasing in height by the same amount each time.

First lets look at the stock suspension: The heavy green line represents the at rest stock horizontal position of the A arm. The ticks on the vertical black line represents the height of each steps. Each thin red line is the A arms position as it reaches the top of each step. Here's where we see what a clever bunch the engineers at Chrysler were. Even tho the vertical movement was an equal amount each step, look at what happens along the circle, the lines get closer together the higher up the steps we go. That shows that the increase in twist of the torsion bar is progressively less as the bumps get higher. THAT'S WHY A TORSION BAR ACTS LIKE AN inversely PROGRESSIVE RATE SPRING rather than the linear rate spring we know it to be!

Is everyone with me so far? Ask questions now about the stock example before I go on to explain what happens when you raise or lower the truck's frame height. Please don't get ahead of the story! We'll all hear how it ends tomorrow...

 

I changed the diagram to read easier.
For the rest of the story: Exagerating for clarity.
Raised vehicle- If you raise the frame relative to the ground, you droop the A arm relative to the ground. (heavy blue line) now as we go up the steps ( thin blue lines) the angular displacement, the space between the lines INCREASES until it's horizontal THEN they start to decrease again.

Lowered vehicle- if you lower the frame relative to the ground, the A arm at rest is angled upwards. (heavy purple line) In this case the A arm has already gone PAST the area where the angular displacement is greatest, so each step will produce significantly less twist of the torsion bar and less movement = softer feel.
To recap: truck goes over a 4 step bump.
Stock: each higher step produces less A arm rotation so torsion bar acts like inversely proportional spring (a "perfect" spring in that the bigger the bump the softer the spring feels!).
Raised: each higher step produces MORE A arm rotation until the arm reaches horizontal, then the rotational displacement starts to decrease as the bumps get higher. Net effect is the spring acts stiffer as the bump sizes get bigger until they are tall enough to move the A arm past horizontal, so the suspension is almost always working in it's stiffest acting range.
Lowered: The A arm rotates significantly less per increase in bump height so the spring feels softer and softer. Since it is starting out at rest in the softer range, it feels quite soft.
Clear as mud?

 

Chuck

Side note. (This smells a LOT like artillery manual gunnery, the manly way, before we had a Pentium 4 just tell us the answer. The Fire Direction Officer is also here today so you’re really in for it now.)

Kidding, but the more you use geometry, as opposed to physics formulas, the better off you are going to be explaining anything to us common FTE folk. I’ll set up a manual firing chart (provided they aren’t all in Iraq) after lunch and follow along. I need to draw angles, and measure distances.

Want my gut reaction? This is going to apply to some degree, but we may have a problem in offering it as a valid explanation in total for ride firmness. I think it is going to apply much more so, in a range of angles that a Volare control arm will never see. We’ll see. I need to draw a detailed and accurate graphical picture for myself.

'fenders (prepared to eat these words later if necessary)

 

Ax, I understand what you are saying and I like the drawing. However, are the blue lines above the green line relevent? Isn't a lowered truck putting the LCArms in a parrallel position which is represented by the green line?

It still seems to me that if the answer is relative to the angle of the LCA, then the effect would be the same for equal deviations in height whether they are above the green line or below. IE: 10 degrees below would have the same effect on ride stiffness as an ajustment 10 degrees above the green line.

Let me float this idea. What if we used your diagram as a tool to describe the angle of the torsion bar on the end that connects to the LCA. (As looking at the torsion bar from the driver's side.)

Let's say that the original manufacturer's position would have been the first blue line below the green line. Now, with that in mind, let's assign appropriate places on the diagram for my truck and fenders'. My angle would be closer to the second blue line below the green line. And fender's angle would be close to the green line.

I am going to say that we hit a bump that requires 1" movement at the point where the LCA and torsion bar meet. So to handle this bump, the torsion bar needs to "flex" 1" in a vertical direction.

I say that because the angle is different for all three settings of the torsion bars above, that the amount of twist, measured in degrees will be different.

Fenders', being the closest to parrallel to the ground would require the least amount of twist to manifest 1" of change. (Ride too soft)

The standard setting would be the first blue line and would require more twisting to accomplish the 1" of change. (Ride just right)

And mine, being the second blue line would require the most twisting to accomplish the 1" change. (Ride too stiff)

To accomplish more twist, the bar would require more energy. Thus, the higher the setting of the torsion bar, the stiffer the ride seems to be. Does this make sense to anybody else? Oh no... the fog's coming in again. John

 

John, I think you are basically saying the same thing in the first 1/2 your statement as I did. I used horizontal for the stock at rest position because most IFS that I'm familiar with are designed for it to be parallel to the ground at rest. I took the raised and lowered positions to extremes to make it visually more obvious the difference in the angular rotation. In real life it would be much more subtle but still noticably significant. only the bottom of the tire moves vertically over a bump, everything else move radially about a pivot point. Yes there is a LOT more going on, but trying to take everything into consideration would require sophisticated 3-D computer modeling that is far beyond me. I've spent 3 years trying to figure out exactly what happens with the unconventional rear suspension geometry on the Celica we race, but I'm no closer today than the day we brought it home. Even the engineers I talked to at TRD (Toyota racing development) couldn't provide any insight. We've had to learn how adjustments affect it by trial and error taking each adjustment to the extremes of it's range to see how it reacts, then find the best combinations somewhere in the middle.

 

When you hit your pot hole the susp not only travels up, the wheel that hit the hole will will also travel reward as far as the complince in the rubber bushing will allow (that is if you have rubber bushings). Also if you lower your susp with relocated ball joints or revised spindles then your arms should remain horizontal.

Fenders: new front shocks are in the garage.

Chuck

 

I think I confused people with the "pothole". All I was trying to say (while injecting some of my dry humor) is that when we are evaluating ride quality we tend to only concentrate on how the vehicle handles bumps i.e. upward thrusting of the wheel, ignoring holes or dips that result in the wheel dropping downward.
I agree that there is a lot of other actions going on, I was trying to look at one specific part that might explain why torsion bars can have different ride qualities simply by changing the preload.

 

AX

I spent a little time constructing a graphical chart with precision instruments. And then measured the resulting changes in vertical interval vs degrees of LCA rotation. It's been a long time. I'm sure there is a trig formula that could have saved me the trouble. But bottom line, I am seeing about a 2% difference per 20 degrees of LCA travel. I laid the angle guage on my suspension tonight. The Volare will only travel a total of 12 degrees from jounce bumper to jounce bumper. John and I are sitting less than 5 degrees apart. You have to reach an angle of 400 mils before the vertical interval becomes sustantial enough to become a major player in this solution. We are far short of that. While I believe your theory is part of the equation. I think it only accounts for a relatively small part of the ride difference.

Sadly, I can't compute my own solution. All I can do is try to disprove yours. Ands offer up the variables I think have to be considered to solve this.

Here they are, for anyone that cares to give it a shot.

LCA to T-bar attachment point 10 1/2"

T-bar attachment point to wheel center 9 1/2

We are dealing with an L shaped T-bar.

Long arm (portion that twists) 27"

Then it rotates at a 90 degree angle on a rubber bushing like a sway bar frame link.

T-bar short arm (no twist, only deflection) 20"

LCA total length from bushing to bushing 13 1/2"

I would be happy to measure any other dimension necessary to compute an approximate solution. And yes, you can recite potential variables to the equation until the cows come home. I am looking for an approximate solution. Just an understandable reason why a non-progressive spring can effectively act like a progressive spring.

Other info that may be of interest. We aren't trying to calculate how a 100# non-progressive magically acts like a 200#. It's more subtle than that. If you stay within approximately 25% of factory preload range, (25% meaning percentage of ride height range), it feels like the spring rate stays about the same. That's my experience anyway, and it is subjective for sure. But radical departures from spec result in a spring that is very noticeably softer or firmer. I've never found a T-bar owner that tried it and disagrees anyway.

 

Dewayne are you taking into account the spring rate of the bar when deciding how significant the difference is? I don't know what the rate of your bar is, but say its 400#/in, a 1/4" of difference in movement is 100# difference in pressure a 25% difference in apparent stiffness resisting the wheel movement. (I think my logic is correct)

 

Chuck

No, there are certainly a lot of things I have not taken into consideration. I am not pretending to know physics. I can't even begin to solve this equation. We aren't splitting an atom here, but it is going to require some computation.

I just got lucky and you posted a possible solution I can graphically portray on a firing chart. I know from manual artillery gunnery that things don't act funny due to vertical angle until it gets way past the 10 or 15 degrees a common IFS is capable of ranging. That is the one and only reason I was doubtful this was the total answer. We are talking about a 2% change in vertical movement due to the angles for the total travel capability of a Volare. That just isn't going to account for it all. I still believe it's a geometry change, but this just isn't all we are looking for.

And 350-400# spring rate is my wild guess of what we are dealing with here. And the day I find out T-bar spring rate can be calculated with a broomstick, a bathroom scale and a five gallon bucket full of cement, you'll find me in the garage trying to compute it. And then I'll be bouncing the results off you and George. I'm too curious for my own good perhaps. I like to modify stuff, and you have to have a clue what you are dealing with to improve it. This has proven elusive. This is one of the most common suspensions of the 70s-80s. If the answer were simple, I would have found it on the web a year ago.

A good old school artillerymen can do a little math and geometry, but we dig the physics out of a chart in a book when we need them. Now the computers do it all. Here's where I run out of gas. Point being, I'll never pretend to be as smart as you, but if you throw something up I can verify, or disprove, I'll be right on it. Count on it. Makes me feel like I am participating in the solution. Even though I'm really not.

And George is working on a theory too. You can be sure he'll run it by us all before we proclaim it the "final answer". He doesn't have a Volare either. And this doesn't need solved today. It's been bugging me for about three years.

And my comment about the Fire Direction Officer earlier. He's the physics guy who will help me on this end when the answer is too hard for me to comprehend.

 

To put your mind at ease, I don't consider myself all that smart otherwise I'd be Bill Gates or invent a cure for cancer, or argue astrophysics with Steve Hawkings. I just have good 3-D visualization and problem solving abilities and greatly enjoy creating beautiful things with my hands, that's why I'm a jewelry designer and no longer in nuclear chemistry. (besides not wanting to glow in the dark any more)
I also read constantly all non-fiction in a mutitude of subjects. We should compliment each other quite well, I'll keep throwing out theories and you can blow em out of the sky!

 

AX

The synergy is our greatest asset on this forum. It took a while, but I usually know who to tap for the right info for most any occasion. I submit if we made a list of who knows each component of the Effie resto equation best. You’d have an allstar team with many names on it.

This is way off the topic. But I always try to remember useful but simple quotes that have served me well. Sometimes they come from the most unlikely places. Sometimes I’ll modify them just a bit.

“How smart a man is has a lot to do with where he is standing at any given time”

(From a silly Burt Reynold’s movie I think). That one taught me not to underestimate people, no matter how “stupid” they appeared to be. I watched a crew or drywallers rock my house. They couldn’t properly read the fractional portion of a tape measure. “One sixteen and five” they’d say, meaning 116 5/8” They couldn’t point to 5/8” inch on a bet. I thought that was just pathetic. They would count five marks, but did not know what it meant. And when they finished in an incredibly short time, the fancy angles by the staircase looked much better than I could ever do.

And now I’ll patiently wait for George to throw out a theory. And if he tells me the T-bar enters from the backside of the control arm. I’ll try to make him a little “smarter” and wait for Revison 1.

 

Let me take a shot at preload.

Within the limited range of rotation of the LCA that we are dealing with here, the tires, through the LCA's, through the torsion bars and their mounts, have to support the weight of the front end of the truck. This weight doesn't change and its therefore its the same regardless of the position of the LCA wihtin the limited range we are talking about. To support this weight, the torsion bars are twisted a certain amount and again if the weight doesn't change the amount of twist doesn't change. Lets say that the bars will twist 10 degrees to support the weight (I don't have the formulas handy to calculate this). This means that whatever the angle of the part of the arm that trails back to the LCA, the other end has to be twisted around the 10 degrees further in order for the arm to end up in the intended position when trucks weight is placed on the front tires. The screw adjustment at the other end of the bar is hard fastened to the bar and determines the position of this end of the bar. The preload is its position such that a 10 degree twist places the arm at the other end in the desired position. If the arm is desired to be in a lower position, the screw end position needs to be backed off by a corresponding amount so that the same 10 degree twist puts the arm in the lowered position. This is adjusting the preload and I can understand completely that it needs to be done while there is no load on the bar.

Did I make any sense here or did I further confuse.

Dwayne, when you desire a firmer ride, are you talking about a flatter ride going around corners or is the mushiness bothering you in a straight line as well. I think I have a theory on that as well, but I think I may have confused enough with the above.

Regards, John

 

"Dwayne, when you desire a firmer ride, are you talking about a flatter ride going around corners or is the mushiness bothering you in a straight line as well. I think I have a theory on that as well, but I think I may have confused enough with the above."

John

It's just plain a little soft. If you back the preload off enough it gets ridiculously soft. What you stated makes perfect sense to me. And George is trying to figure out why Volare's act weird. If you change the preload, it should not theoretically effect the "firmness" one bit. And I can line up 2 dozen T-bar owners on a moments notice that will tell you different. When you stray far from the factory setting, the ride becomes either softer or firmer. If you stay near the middle, I don't notice a big difference. JagRed John has even managed to achieve a firm ride, with preload as far as I can tell from his description. Seems strange, but he has company in making this claim. Joe Gaddy is complaining of a firm ride as well.

George will share his thoughts soon enough, but it has been suggested he work on it when it's too cold to play in the garage. I don't want him to waste any quality time with Earl. We'll sure entertain your theory. In the end, I won't be amazed if George says there is no logical explanation to what I and my friends claim occurs. If that's the case, we'll have to accept that and go on from there. This isn't exactly a laboratory.