I have a dual spring rate / lift height puzzle for you...

[4x4junkie]

Y'all are waaaayy overthinking this and confusing a (single) progressive-rate coil spring with the two individual springs you'd put onto a coilover to create a progressive rate coilover (the math you're trying to apply here applies to the ratings of two separate springs to find the overall rating for them together).

Rubydist is correct. On a single spring like you have here that is made from one length of wire, the lower spring rate figure is for the entire length of the coil spring (385PPI is what you have before the upper coil windings make contact with each other). When the coils do make contact, the spring then becomes 650PPI.


So 1100lbs @ 385PPI would be 2.857" compression.
18.625 (free length) - 2.857 = 15.768" (compressed length).
15.768" - 10.5" (stock compressed height) = 5.268" (the amount of lift height)

What we still don't have here though (and is what rubydist was attempting to get at initially) is at what point in the amount of spring compression does the spring rate change from 385PPI to 650PPI? If that happens before 2.857" of compression is reached, then the 5.268" lift figure goes right out the window. Hopefully this does not occur before 2.857" because that would actually defeat the purpose of having a progressive coil since you'd then be riding on the 650PPI section most of the time.

On the lever thing, Hound is on the right track. It has to do with the way the beam pivots off the frame, and the fact the coil spring is at a mid-point along the beam (a solid axle does not function as a lever, the entire thing moves as one, the coil springs compress at the same speed the suspension moves, so no leverage ratio applies).

Years ago I had made a diagram to help explain this, but for some odd reason it's disappeared off my computer, and interestingly it seems to have vanished from the 'net as well (it was an overhead-view diagram of the TTB w/radius arms with red lines to show the TTB pivot axis, and separate green & blue lines to show the difference in lever length from the pivot axis to the tire contact patch, and from the pivot axis to the coil spring. The line leading to the tire was approx 1.5× longer than the line to the coil spring.
If you need, I can try to recreate the diagram, though my printer/scanner has been a little temperamental lately (the original base image I used was from my '94 FSM).


Edit
Geez, this thread is moving quick lol
Floored's numbers about match mine, and again we're trying to guess where the transition from soft to stiff occurs.

Progressive rate springs IMO are a headache, and really offer nothing to boot. If you need more resistance to the suspension bottoming out in whoops and dips, it's better to achieve that through shock valving/bypass shocks, perhaps combined with hydro bumps. Progressive springs do work better on the rear though where you might be carrying different weight loads (leaf springs having an overload leaf are progressive rate).

 

[bobbywalter]

Not 100% sure. But my thought is that it comes from the way the ttb works. You have 2 different lengths to consider; axle beams pivot to spring perch and axle beams pivot to wheel centerline. The weight of the truck pushes down on the axle beam at the spring perch, length A. Then the weight is transferred to the ground via the wheel, length B from the pivot, which is longer than length A. The lever arms are different, so the forces are different.

To further complicate matters, the passenger side axle beam is a different length than the driver side beam. So if you build both sides identical, you get different results. It's noticeable when you go to do the alignment or start measuring and comparing compressed spring heights from one side to the other. This may even contribute partially to the proverbial "Ranger lean" issue that we normally attribute to fuel tank placement, driver position, etc.

To expand on all that, you might be thinking "IFS setups and solid axle setups also have a difference between the pivot to spring length and pivot to wheel length". And that is true. But, in IFS, those lengths are much shorter than ttb. I don't know exactly how that affects it. The length (lever arm) from pivot to spring perch probably close to 1/2 the length from pivot to wheel center. It probably just makes the math easier for the engineers. In a solid axle setup, you have a much longer lever arm. But there's another catch. The axle is not pivoting from a fixed point on the frame. It pivots off of the opposite wheels contact with the ground. It's a whole different beast. In fact, if just one side is being raised by a rock, it actually puts upward force on the frame on that side AND a much lesser lifting force on the frame on the other side. So both sides of the vehicle are being lifted. Whereas with ttb, the side with the rock is lifted and that lifting force, raising the frame actually unloads the opposite side slightly.

motion ratio.

but ttb is a triangle fighting steering ang.

 

[bobbywalter]

Y'all are waaaayy overthinking this and confusing a (single) progressive-rate coil spring with the two individual springs you'd put onto a coilover to create a progressive rate coilover (the math you're trying to apply here applies to the ratings of two separate springs to find the overall rating for them together).

Rubydist is correct. On a single spring like you have here that is made from one length of wire, the lower spring rate figure is for the entire length of the coil spring (385PPI is what you have before the upper coil windings make contact with each other). When the coils do make contact, the spring then becomes 650PPI.


So 1100lbs @ 385PPI would be 2.857" compression.
18.625 (free length) - 2.857 = 15.768" (compressed length).
15.768" - 10.5" (stock compressed height) = 5.268" (the amount of lift height)

What we still don't have here though (and is what rubydist was attempting to get at initially) is at what point in the amount of spring compression does the spring rate change from 385PPI to 650PPI? If that happens before 2.857" of compression is reached, then the 5.268" lift figure goes right out the window. Hopefully this does not occur before 2.857" because that would actually defeat the purpose of having a progressive coil since you'd then be riding on the 650PPI section most of the time.

On the lever thing, Hound is on the right track. It has to do with the way the beam pivots off the frame, and the fact the coil spring is at a mid-point along the beam (a solid axle does not function as a lever, the entire thing moves as one, the coil springs compress at the same speed the suspension moves, so no leverage ratio applies).

Years ago I had made a diagram to help explain this, but for some odd reason it's disappeared off my computer, and interestingly it seems to have vanished from the 'net as well (it was an overhead-view diagram of the TTB w/radius arms with red lines to show the TTB pivot axis, and separate green & blue lines to show the difference in lever length from the pivot axis to the tire contact patch, and from the pivot axis to the coil spring. The line leading to the tire was approx 1.5× longer than the line to the coil spring.
If you need, I can try to recreate the diagram, though my printer/scanner has been a little temperamental lately (the original base image I used was from my '94 FSM).

the math works the same with the single coil. the whole point of progressive rate springs.


your diagram is still out there

lots of people are putting ttb on jeeps and other rigs now. they have it

 

[4x4junkie]

the math works the same with the single coil. the whole point of progressive rate springs.


your diagram is still out there

lots of people are putting ttb on jeeps and other rigs now they have it

No, you and Jim were trying to apply math for two individual coil ratings (and is why you kept winding up with the 250-ish number). 385 is the actual PPI until the windings touch, then it's 650.

 

[bobbywalter]

No, you and Jim were trying to apply math for two individual coil ratings (and is why you kept winding up with the 250-ish number). 385 is the actual PPI until the windings touch, then it's 650.

i used to think that, then i was schooled a bit out where you live. i dont remember if it was the foa guys or the hut next to them. they had a press and were testing units. 2010 or 13..

 

[4x4junkie]

i used to think that, then i was schooled a bit out where you live. i dont remember if it was the foa guys or the hut next to them. they had a press and were testing units. 2010 or 13..

Well, I'm not sure if maybe we're misunderstanding each other, but I 100% guarantee you the PPI of a progressive coil spring (such as the ones Jim posted the photo of in the OP) before any windings touch is the lower of the two numbers (when the coils touch, then it becomes the higher number).

The number I got now (closely) matching what is claimed for the spring's lift height further supports this.

I tried every search term I could think of that might be in any discussion surrounding that diagram, and it produced many other images I had created or worked on about a TTB (it's amazing how an image can proliferate around the internet from the site it was originally put on lol), but never did the one I was looking for pop up. It's strange, because I remember putting it on numerous sites (here, P4x4, EF, BII.org, probably more... Only that last one I know is defunct)

 

[bobbywalter]

ok .... thinking deeper of exactly what we were doing, while those were single wind dual rate springs. they were not free running 5 in or more truck springs. they were for a coilover application..with a single spring and used for travel purpose.

i understood that as why i was crushing my progressives ...which i was on leafs at that point but looking to get back on coils....and for sure once under 250 they can self eject by bowing out on a ttb. i had that issue

so i think you are right, Ruby is right i had to use canted seats due to operating angle of the beams. its why the bumps are the way there are on cherocars and why the math is off.


there are a slew of calculators. with ttb its never right

 

[alwaysFlOoReD]

I remember that diagram.

 

[bobbywalter]

i know its out there, i seen it when they were building the setup for a 78 bronco for layout, and on a jeep discussion... and laughed.... i knew Shawn made it

 

[Jim Oaks]

There's been many times I've searched the internet for something, and it brought me right back to here. I just saw a post where a guy was talking about TTB and said he found the information on another site, and he as quoting @4x4junkie article HERE.

@alwaysFlOoReD I actually posed this question to ChatGPT but didn't ask it as well as you did. So, garbage in, garbage out. LOL. Maybe you should ask it to explain the 1.5 leverage of the TTB and what effect it has on spring rate.

The point in all of this is trying to give people some guidance when trying to figure out how much lift their going to get from a coil spring and what to expect. But I didn't know how to address progressive rate springs.

I have to admit, I was a bit surprised when JD told me their springs were 385/650. 650 seems like a really high rate.


Ok @4x4junkie I'm going to throw a few more questions at you:

1) Why would the second rate be so high for a Ranger?

2) I'm trying to understand why we're only using the lower rate. Is it because the section of coil with the 650 PPI rate won't compress at all because the weight is being absorbed by the coils rated at 385 PPI? Is that weight not transferred through the whole coil?

When I was creating that coil spring page, I wondered where the 1.5 leverage came into play if at all.

Back in 2006, glfredrick posted on Pirate4x4 (HERE) "Before you just go throwing a bunch of springs at the TTB suspension, you have to know a little bit about the geometry of that suspension. Each different type of suspension has a different amount of leverage needed to support the weight of the vehicle. An SAS (full width axle) is a "longer lever" than a TTB. That means that the carrying capacity for the springs needs to be less on an SAS than on the TTB."

I looked at coil spring rates between a Ford F-150 Dana 44 and Dana 44 TTB and didn't see any big differences between spring rates. I went back and looked at the load rates, and a 1985 Ford F-150 coil spring has a load rating of 1,428 and a 1979 Ford F-150 coil spring has a load rating of 1,700.

Junkie, you replied in that conversation with "Multiply the sprung weight by 1.5 (TTB beam leverage), then divide by 2 (this will be the amount of weight each coil will be supporting)." But I haven't been able to support that by finding Dana 44 TTB coil springs with higher spring rates than a Dana 44 live axle. I'm not saying you're wrong, I was just looking for a reference to 'show me' so that I could actually understand it.

I would really like to understand this more and what importance or effect that it has.

All of this TTB suspension talk makes me want to make my own suspension again.

There are probably only a few people here that remember this, but back in around 2001, Joel (CopyKat) designed a heavy duty 8.8-inch diff cover (TRS-2 has one) and we began selling them through The Ranger Station. And then in 2004 I began designing our own TRS TTB drop brackets. I designed the bracket for the driver side beam, and Joel designed the one for the passenger beam. This is the bracket that some companies just offered an extension plate for to lower it. Joel actually cut these pieces and made a set. I know he sold a few of them. I think he had to do a slight design change to one of them, but I don't remember which one it was. Regardless, I know some people out there have TTB brackets that both of us designed. I'd really like to make a set someday since I have all of the drawings, I just don't know if the drawings are before or after he made a correction to them. I have the drawings for the diff cover as well.

 

[alwaysFlOoReD]

I bought a set. They are still boxed up buried somewhere in my crap that I've moved 3 times since buying.... I'll look for them tomorrow and compare to your drawings.
The progressive coil is one long piece of spring steel that is one diameter. So the rate is the same for the whole length, until the coils touch and then it is suddenly much shorter and the rate changes because the length changes. That is how I came up with the 5/13 ratio, I counted coils for the whole length and that was 13. I count coils for the coils spaced close together and that was 5. 5/13 is very close to 1/3.
I'll ask ChatGPT about ttb when I get up in the morning.

 

[rubydist]

The spring rate is determined based on the diameter of the wire, the modulus of the material in the wire, and the length of the wire. The longer the wire is, the easier it is to twist it (lower rate).

It sometimes helps to think of the spring like a torsion bar (a coil spring is just a torsion bar that is wound in circles). The initial spring rate of this spring is 385 lbs/in because when we first start to compress the spring, we are twisting the entire length of the wire. After some point, part of the coils are fully compressed (to bind) so that portion of the wire no longer twists as the spring is further compressed. This effectively shortens the length of the spring, making it stiffer.

In this type of spring, you want to be working in the lower spring rate range of the spring for "normal" use, and only get to the stiffer part under extreme loading/compression. This is to avoid bottoming out the spring in those extreme situations. I personally think the difference in rate of this spring is too much(it gets 68% stiffer after the transition), but to each his own.

 

[Jim Oaks]

I bought a set. They are still boxed up buried somewhere in my crap that I've moved 3 times since buying..

If you ever decide to sell them let me know.

I'll ask ChatGPT about ttb when I get up in the morning.

Well??

The spring rate is determined based on the diameter of the wire, the modulus of the material in the wire, and the length of the wire. The longer the wire is, the easier it is to twist it (lower rate).

This is a great point and makes sense. I know that you measure spring rate by using the diameter of the spring wire, the mean (basically the outside diameter minus the spring wire diameter) and the number of free coils. When these closer spaced coils come into contact with each other they are no longrr free. So if you reduce the number of free coils, your spring rate goes up.

Now it makes perfect sense why you use the lower number, and how springs get a dual rate. If one of the upper closely wound coils were spread out like the lower coils, the higher spring rate (650) would be lower.

 

[alwaysFlOoReD]

ChatGPT - TTB Spring Rate Calculation

Shared via ChatGPT

chatgpt.com

 

[Jim Oaks]

ChatGPT - TTB Spring Rate Calculation

Shared via ChatGPT

chatgpt.com

Pretty good information, but it gave me a motion ratio of 0.70.

Beam mount to spring mount / Beam mount to wheel center

So I still have to dive more into this 1.5 leverage issue.