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If it is there make me a believer! I would think the way to do it would be have the weight on lower a arms and lower one as that should make the center get closer to the cross member and easy to see or measure, if I read the sketches correctly.
The last time I had mine apart the top of the spring was worn. Which suggests the spring does move. I don't think it is that much as the stock spring was not worn. Mine is lowered which puts the spring closer to the top.
I'm interested in the clay test! I was not able to compress the suspension with the stronger springs on mine the car would lift off the jack stands before getting to ride height.
the middle of the spring cannot move where it is bolted to the chassis
Originally Posted by blackozvet
there is no way that spring "moves" in the middle of the 2 brackets.
If you read what the article said, "the centre of the spring - between the two clamps - WANTS to rise and fall in the opposite direction from the ends" It WANTS to but it CANT, because it is solidly clamped 18" apart.
Originally Posted by ddahlgren
If there is no lateral movement allowed the flex in the middle can not happed as the length between mounting points changes when the bend in the center happens.
Originally Posted by blackozvet
some people are trying to say that its not solidly mounted and can move around between the 2 mounts, Im sorry but I just cant see that happening ?
Originally Posted by ddahlgren
If it is there make me a believer!
Guys....the spring moves in the center -in between the two mounts. It moves.
Here it is on stands, suspension in full rebound (as much as the shocks will allow). The center of the spring is about 2.25" from the cut out in the cross member.
Here it is with the front, now supported by the wheels, the center of the spring is about 1.8" from the cut out in the cross member.
Label me a believer then that it moves. At the end of the day this ends conjecture around sales and GM sponsored data with real world data.! My position has changed on the spring bending in the middle. Not sure about how it might change roll stiffness but certain the center deflects. The rest to consider.
ok, lets not get carried away, this is what happens when 1500 pounds of weight is pushed against 24 year old rubber suspension bushes !
less than 1/2" of rubber compression, thats to be expected. there wouldnt have been that much movement when it was new.
but it does show up an issue in the c4 front end, who ever considers upgrading the rubber bushes in the spring, only people who put lowering wedge kits in.
a lot of people replace all the bushes in the front end with Poly, whoever thinks of replacing the spring rubber ?
There is very little rubber mount on mine barely any at all. Maybe 1/8". The spring moves in the middle, it has rubbed a large but shallow mark on the top.
ok, lets not get carried away, this is what happens when 1500 pounds of weight is pushed against 24 year old rubber suspension bushes !
less than 1/2" of rubber compression, thats to be expected. there wouldnt have been that much movement when it was new.
You can lead a horse to water....
The "rubber compression" is in the wrong direction -to blame the movement on "rubber compression". The spindles went UP...center of spring went DOWN. Spring is working just like Dave and the chassis engineers are talking about in the text that I posted earlier.
in the first picture, is that both wheels off the ground ?
a better experiment would be to attach a tape measure between the inside of the 2 spring mounting points, jack up and down and see if that distance changes.
Yeah. It is. Both wheels were off the ground. I thought that I stated things pretty clearly. Let's have a look;
Originally Posted by Tom400CFI
Here it is on stands, suspension in full rebound (as much as the shocks will allow).
Yep. That seems pretty clear. At least to me it does. IDK though...
Then, for the second picture I said:
Originally Posted by Tom400CFI
Here it is with the front, now supported by the wheels,
-Which is as close to the opposite of "full rebound" as I could get w/o putting a press or massive weight on the front of the car.
Originally Posted by Tom400CFI
a better experiment would be to attach a tape measure between the inside of the 2 spring mounting points, jack up and down and see if that distance changes.
Absolutely not. That would be a terrible experiment. Why? B/c the spring's movement in a lateral direction is so infinitesimal, it would likely be unmeasureable by tools that the average home owner has....and it would certainly be unmeasureable with a tape measure (?)
No, the BEST way to see if the "spring "moves" in the middle of the 2 brackets.", is to observe the very deflection that has been debated in this thread! That would be the vertical movement of the spring, between the mounts -the very movement YOU said "doesn't/can't happen". That movement is exactly what I observed, measured, photographed and posted for the forum. Can't really get more straight forward than that, but MAN....you never know on these forums. I've had guys tell me there are holes for air where there is no hole. So....IDK how to demonstrate it any more clearly. A video? You can do it, this time. Your turn.
Wow, I was busy the last few days and missed some stuff!
Originally Posted by blackozvet
so what happens when you mount another spring (being a leaf spring v a torsional spring but a spring never the less) at the same points, bottom arm - 2 chassis points - bottom arm, it will transfer force from one suspension arm to the other, load the other tire and create roll stiffness.
How much roll stiffness does a leaf create ?, in the article that was originally posted by boot77 ? they claim 80% more roll stiffness, which sounds a lot but they are most likely referring to roll bar rate. We know that a 1 1/4" swaybar is 2.4 times as stiff as a 1" roll bar (stiffness = D4) So while the engineers were claiming they needed less swaybar with a leaf, its probably the difference between a 30 and 32 mm bar.
And why was it all so important, because the c4 chassis lacked torsional rigidity, and needed big swaybars.
All your stuff about where things are mounted is just irrelevant and not even comprehensible. You missed the point of the 80% thing also. All springs in all vehicles resist roll: most of them resist it at the same rate they resist heave and dive. But the engineer was saying that the C4 leaf spring by itself provided an 80% higher wheel rate in roll than in heave/dive. That's a very big difference.
And no, roll stiffness has nothing to do with torsional stiffness. In fact, a chassis that is very flexible in torsion generally requires lower spring and roll rates, because it can't react large differences in roll rates between the front and rear. You're conflating things and trying to turn this into voodoo magic.
Tom, thanks for doing those measurements. As you saw, when I jumped into this thread I didn't believe in the anti-roll properties of our leaf springs. But I get it now. Your patience and tech is appreciated.
Here it is on stands, suspension in full rebound (as much as the shocks will allow). The center of the spring is about 2.25" from the cut out in the cross member.
Something doesn't make sense here. With the suspension hanging, the dimension is 2.25". With the suspension loaded, the dimension is 1.8". That's SMALLER! That says the center of the spring moved UP in relation to the frame, as the spring flexed!
Edit: Okay, I see my error. I was looking at the pictures wrong. Sorry Tom.
Last edited by Hot Rod Roy; 09-24-2016 at 08:38 PM.
The "rubber compression" is in the wrong direction -to blame the movement on "rubber compression". The spindles went UP...center of spring went DOWN. Spring is working just like Dave and the chassis engineers are talking about in the text that I posted earlier.
The compression would be in the wrong direction, if we were discussing a vertical coil spring, but we arent. We are talking about a transverse upside leaf spring, and the energy and force travels in a different direction.
I stick by my point that the leaf doesnt bend in the middle, if the leaf could slide in the 2 brackets it could, but it cant. The only movement is that allowed by the compression of the (20 to 30 year old) rubber bushes.
I understand that some people dont agree, and Im ok with that, I understand that Tom thinks he is 100% right, and Im ok with that, we can agree to disagree. I think we are getting emotionally over invested in this argument and that isnt a good thing, so Im done with this discussion.
Just to prove I could be wrong, I have found a picture of a spring bending in the middle,
Something doesn't make sense here. With the suspension hanging, the dimension is 2.25". With the suspension loaded, the dimension is 1.8". That's SMALLER! That says the center of the spring moved UP in relation to the frame, as the spring flexed!
The spring is mounted above the subframe that Tom was referencing. So as the dimension got smaller, the center of the spring was moving down.
Originally Posted by blackozvet
I stick by my point that the leaf doesnt bend in the middle, if the leaf could slide in the 2 brackets it could, but it cant. The only movement is that allowed by the compression of the (20 to 30 year old) rubber bushes.
So even though Tom measured a flex of 0.45" between no load and static resting load, you refuse to believe it? That is impressive. I guess Tom was right:
If I follow this along after making a quick sketch does this work as follows?
When making a left turn the spring on the right side goes up causing a bow down in the center of the spring and the left side of the spring goes up taking load off the right side of the suspension.
If this is correct and agreeing the center of the spring does move how does taking load off the left side make the right side stiffer and reduce roll greater than the right side spring rate?
With an anti roll bar the spring rate of the left side spring is added to the right side spring at a rate and amount dictated by the size and mounting of the anti roll bar rather than just lifting the left side spring.
Something doesn't make sense here. With the suspension hanging, the dimension is 2.25". With the suspension loaded, the dimension is 1.8". That's SMALLER! That says the center of the spring moved UP in relation to the frame, as the spring flexed!
The measure ment is taken from the bottom, so when the suspension is "hanging"...in full rebound, the spring makes one big arc....the middle of the spring is higher/further from the bottom of the x-member, which is below the spring. Compress the front suspension, and the spring flattens out...the middle of the spring goes down as it flattens...so it's lower in the middle/closer to the bottom of the x-member, which is below the spring.
When making a left turn the spring on the right side goes up causing a bow down in the center of the spring and the left side of the spring goes up taking load off the right side of the suspension.
Correct. IDK that the spring "goes up" on the left but downward force is certainly reduced on the left side, contributing to roll resistance.
Correct. IDK that the spring "goes up" on the left but downward force is certainly reduced on the left side, contributing to roll resistance.
For illustration only lets say the front spring is 500# per inch on both sides at the wheel rate and no I have no idea if this is right or wrong in actual numbers and picked out of the sky only to have some starting point.
Lets say on the previous mentioned left hand turn the right front travels down 1 inch and 500# is used to resist the suspension drop and the left side goes up an equal amount of 1 inch as the spring is symmetrical and no mention has been made of asymmetric response.
This will make the left front drop so the car feels flatter but adds zero in roll stiffness as subtraction from one side does not add to the other.
If you have an anti roll bar it uses the spring rate from the left side to add to the right so a net increase in roll stiffness at an amount dictated by bar size and mounting. In one respect this makes the 'feature' a potential liability if the spring is going up on the left and offering less resistance what will offer resistance to the anti roll bar?
This not as simple as GM might indicate in what is published in my mind.
Just thinking out loud keeping open minded discussion going.
09-21-2016, 10:51 AM
