Leaf Springs Vs. Everything Else

[GATA79]

Hey guys,
I've seen a ton of posts on here similar to "4 Link from company X vs. Torque Arm from Company Y" etc etc, but no one really actually discussing the true comparison of these new systems vs. what we have/the old school route.

I wanted to open up a discussion on ya'll experience, and thoughts of the original leaf springs vs. 3/4 link vs. torque arm setups.

What are we gaining with going with these new design setups? Is it really worth the ticket price over a good leaf spring setup?

I'm coming to the point in my 2nd Gen F-body PT build to start seriously considering rear suspension. I'll be at 550tq easily, and am weighing out all my options and also feel a thread discussing these differences could be beneficial to others in the same boat.

Torn between the PTFB Comp Kit (traditional leaf springs), and the BMR Torque Arm basically, but would really like to turn this into a good discussion speaking of the advantages of these systems over the leaf spring design.

Lets get it started! What do you guys think?



JJ

[Rotary]

Hmm I don't have the knowledge to say whats best. I've been browsing my options and rear cantilever suspensions are also starting to come to market for my car. It would be great to see some opinions from people who have own the products or know alot more about them. Are they better than leaf springs enough to warrant the cost?

[astroracer]

The first question you should be asking yourself is: What is the purpose of this car? What will it see for 95% of it's driving life? Track only? Street only? Mostly street with MAYBE a little track time?
When I was developing the van suspensions I talked with Mark Stielow about this exact same subject. He told me a well tuned leaf spring suspension will hang with most any aftermarket suspension available at that time. Good bushings, good shocks and a tunable stab bar will get you there.
It really depends on what you are going to do with the car and how much better you "think" a new suspension will be over the old leafs.
I went away from the leafs on the van build (sadly...) but that was due to not being able to find anything that would fit the new chassis. The stock Astro springs were just too long and having a pair custom made was more exspensive then building a 4 bar set-up.
If money is the object, and I know it is on many builds mine included, a few dollars spent on optimizing your leaf springs will be money well spent and create less tear-up on the car.
Mark

[High Plains Mopars]

I've often thought of it this way, tires only care about the force applied to them. Force can come from any type of spring and when you come right down it, there are only four type - leaf, coil, torsion, and air. So then it may come down to packaging, cost, or appliciation.

Leafs typically are long, which means packaging them in a chassis may be an issue. They also are somewhat heavy, so weight can be an issue. If you are racing on multiple venues, it can be difficult to carry around enough springs to change out a 50# rate to get the perfect combo. They also tend to be more expensive to get a good pack of leafs.

With that said, however, unless you need all those above criteria to be met, leafs can be a very competitive and at times, a forgiving means of suspending a car. If you car has come with leafs, then the design factor is mostly covered. You may need to move them in some for tire clearance, but there are kits out there to do this. You can use composite springs to reduce the weight issue. They are not easy to change, so if you need to swap out rates regularly, there is not much of a way around that issue.

Consider this, the 1970 trans am series required leaf equiped cars to retain those leafs. Sure they modified them over stock, but those cars ran plenty fast lap times and handled on a par consistent with many set ups of today. So it can be done. IMO, budget, application, and personal desire will be the biggest concerns on ditching or retaining leaf springs these days.

[TheBandit]

I've often thought of it this way, tires only care about the force applied to them. Force can come from any type of spring and when you come right down it, there are only four type - leaf, coil, torsion, and air. So then it may come down to packaging, cost, or appliciation.

I think you're missing an important point which is that the kinematics of the suspension dictate where/how loads are applied & transferred under dynamic situations. Most leaf spring suspensions use the spring to locate the axle, so it is serving multiple purposes in addition to providing spring rate, for example lateral location, resisting axle torque, locating the roll center, determining ride height, etc. Link suspension designs tend to offer more independent adjustment of geometry.

I think Astro's post is right on point. How are you going to use the car? Link suspensions carry a hefty premium. You may very well be happy with a good leaf suspension and put the saved money into other upgrades.

[tflyboy77]

If you were a little closer to Indy I would be happy to take you for a spin in my 550hp 600tq 77 t/a with the ptfb comp kit. I've been autocrossing it recently and I've been very happy. If you've got any questions feel free to pm me.

[regal454]

There are alot of great cars runnung around on leaf springs. Here is a link to the build thread of Mary Pozzi's 2nd Gen Camaro. Her car is awesome!!

https://www.pro-touring.com/showthre...ct-Jenny-Craig

[BonzoHansen]

There are alot of great cars runnung around on leaf springs. Here is a link to the build thread of Mary Pozzi's 2nd Gen Camaro. Her car is awesome!!

https://www.pro-touring.com/showthre...ct-Jenny-Craig

her car has a hotchkiss 3 link. but yes, she ran very well for years with leaf springs.


budget & intended use are the primary questions to answer.

[TheBandit]

her car has a hotchkiss 3 link.

When did that happen? Is there a build thread?

[John Wright]

When did that happen? Is there a build thread?

Search for "Jenny Craig" <---name given to the car after it lost weight.


EDIT: Here ya go

https://www.pro-touring.com/showthre...ht=Jenny+Craig

[regal454]

When did that happen? Is there a build thread?

There is a link in post #7 ^^^^^^^

[John Wright]

There is a link in post #7 ^^^^^^^

Whoops! I missed the earlier link...sorry for the duplicate

[srh3trinity]

There have been some very fast cars on the board with leafs. In my mind, you lose some adjustability with leafs. There is a such thing as too much adjustability, but you would have more with the TA setup. The Pozzi's ran leafs for a good while and Mary was very fast on leafs, but I know I read some posts where they had run different leafs with different bushings and had given up some street comfort for performance before they finally settled on the Hotchkis setup which they felt like was the best of both worlds being both fast and having decent ride quality.
Price, packaging, needs/desires, tire width are other things that factor into the equation for many.

[GATA79]

For arguments sake, lets say an all around build. Mine in particular I want something I can be competitive with on the Auto-X, drive to and from these events, drive on sunny days, drag, basically a well rounded, fun car. This thread has sparked some good discussion lets keep it up! I'm really swayed towards the PTFB Comp Kit honestly. Or going with DSE's rear kit.

[Twentyover]

I'm likin' the direction this is taking.

I have a car that no one makes a suspensoion for. It's on leafs, staggered shocks, no otherlateral location beyond springs.

Is the key detaching the spring function from the location function? Put a set of sliders, cal-tracs,and a panhard and tune from there?

[Rotary]

I'm likin' the direction this is taking.

I have a car that no one makes a suspensoion for. It's on leafs, staggered shocks, no otherlateral location beyond springs.

Is the key detaching the spring function from the location function? Put a set of sliders, cal-tracs,and a panhard and tune from there?

Did a google on the cal-tracs and pan hard for my particular application. A nice set up between the two of them is $700ish plus shipping. The panhard i found are from maier racing and is a race set up. So with this type of set up you would have to get your ride height dialed in with your shackles and leafs? I like the price vs 3k irs systems.
Not trying to steal your thread Gata, its the first time i've ever really looked at a modified leaf set up as compared to pricey options, I'm following this one pretty closely myself.
http://www.mustangdepot.com/OnLineCa...ion/mr-phr.htm

[High Plains Mopars]

I think you're missing an important point which is that the kinematics of the suspension dictate where/how loads are applied & transferred under dynamic situations. Most leaf spring suspensions use the spring to locate the axle, so it is serving multiple purposes in addition to providing spring rate, for example lateral location, resisting axle torque, locating the roll center, determining ride height, etc. Link suspension designs tend to offer more independent adjustment of geometry.

No, I'm not missing that point. That is why I said it can be a very forgiving suspension design. While the leaf does do all those things, it doesn't diminish its role as a spring nor make it any less of a performer for the average guy. Yes, a coil set up allows individual components to be added to perform specific tasks, and potentially allow more defined adjustment in those roles, whereas a leaf spring set up has to perform all those same functions and cannot be as easily designed to accomodate simple or easy changes. I'd also say if you understand the traction circle concept, you know that any tire will only generate X amount of grip. That grip can be accellerating, braking, turning, or any combination of those. The loads a tire sees under braking or accellerating are X-Y. The loads felt during cornering are X-Z. The combination of turning and either accelerating or braking is X-Y-Z. Simple as that. Regardless of what device is doing what in the suspension, when those loads are applied or transfered, the tires will feel those formulas and will only generate as much grip as it is designed to. The spring design applying that force in your average street car is less important than the amount of that force and rate at which its applied. If you stab throttle and crank the steering, you're going to overload a coil as quickly as you overload a leaf. If you have too much rate going in to a corner, you will overload a coil as quickly as a leaf.

For arguments sake, lets say an all around build. Mine in particular I want something I can be competitive with on the Auto-X, drive to and from these events, drive on sunny days, drag, basically a well rounded, fun car.

By competitive at the autocross, do you mean an SCCA or NASA street prepared class where there are rules limited the available mods you can perform to specfic classes, or the all out, free for all of a Goodguys autocross? In one, you have to retain the leafs or move to higher level classes that may eliminate your competitive ablity to more dedicated race equipment. In the other, it doesn't matter what you put under your car. In both, your driving skill will be the most important component of your car. Budget and desire for tuning are bigger factors than those listed. A leaf spring can be tuned, but it is not easy. A coil spring, as the Bandit pointed out above, often has more components readily available to allow adjustment to a larger variety of variables. Let me ask you this, do you want to spend time creating a log book and tracking every change to each setting and recording the results to ensure you don't head in the wrong direction or you can correct it if you do?

I'm likin' the direction this is taking.
Is the key detaching the spring function from the location function? Put a set of sliders, cal-tracs,and a panhard and tune from there?

Not necessarily. Leafs function very well in their roll and even the addition of a lateral locating device still requires the spring to act as a fore/aft locator. You cannot entirely eliminate the dual role of locator and spring with a leaf. Not with sliders, cal-tracs, or a panhard. However, the addition of a properly designed watts or panhard that has vertical adjustment will add a simpler roll center height change capability, which can be used to tune lateral traction. more quickly and easily than just a leaf design.

Alteration of the front and rear eye locations can be changed and allow tuning of anti-squat and instant centers. However, this is a drawback in the leaf design in that these points are not easily adjusted on a finished chassis and they movement would best be designed in during the build. Even then, they have a limited range where they are effective. Don't forget that asymetrical vs non asymetrical arc design can be a tuning attribute to alter anti-squat as well as a traction aid. This is in basic theory how a cal-trac works. By creating a dynamic front segment length change under load to create a stiffer front section to aid traction, it allows you to put down more power more aggressively than you could with a purely symetrical designed spring. Think mopar Super Stock as a classic example.

Similarly, setting up leafs with positive or negative splay compared to parallel mounting can also be used as a tuning device to reduce/increase roll steer characteristics as well as add roll resistance.

[TheBandit]

No, I'm not missing that point. That is why I said it can be a very forgiving suspension design. While the leaf does do all those things, it doesn't diminish its role as a spring nor make it any less of a performer for the average guy. Yes, a coil set up allows individual components to be added to perform specific tasks, and potentially allow more defined adjustment in those roles, whereas a leaf spring set up has to perform all those same functions and cannot be as easily designed to accomodate simple or easy changes. I'd also say if you understand the traction circle concept, you know that any tire will only generate X amount of grip. That grip can be accellerating, braking, turning, or any combination of those. The loads a tire sees under braking or accellerating are X-Y. The loads felt during cornering are X-Z. The combination of turning and either accelerating or braking is X-Y-Z. Simple as that. Regardless of what device is doing what in the suspension, when those loads are applied or transfered, the tires will feel those formulas and will only generate as much grip as it is designed to. The spring design applying that force in your average street car is less important than the amount of that force and rate at which its applied. If you stab throttle and crank the steering, you're going to overload a coil as quickly as you overload a leaf. If you have too much rate going in to a corner, you will overload a coil as quickly as a leaf.

First, let me apologize for using the term "missing the point". I think that was inflammatory and that's now how I meant it; I only meant to add information to the already good information you provided.

Yes a spring is a spring and spring rate is spring rate, however the geometry/kinematics of the suspension dictate kinematic properties which will determine how the tires are loaded. I'll take roll stiffness as an example. Depending on where the roll center is located, a given spring rate at either side of the axle will result in a different roll stiffness. Even if the rates of a coil and a leaf are the same, if the roll center is different, the roll stiffness will be different. This affects the ratio of roll stiffness front to rear, which will determine how loads are transferred when cornering. For example, if the front has a higher roll stiffness than the rear, more load will be applied to front outside tire in a corner. You will operate in a different part of the traction circle for each tire because the applied loads are different. This is just one example that I am aware of. There are other suspension properties like antisquat which are much more constrained with a leaf spring design than a link suspension.

[High Plains Mopars]

Sure, you can make a leaf spring car handle really well. Does it make as much sense to start there as opposed to a linkage and coil system? No.

Agreed and I'd add that if you have to significantly re-engineer the leaf spring layout to make it work for your application, then it may be better to start with a link set up. For most of us using these vehicles as predominately street cars, an aftermarket leaf layout can be a much simpler and more economicly friendly approach to get our butts in the seat and the car out of the garage.

A panhard bar is good. A watts link is better. However, leaf springs have their own roll center. To add a second locating device that forces the car to roll about a different center can create binding and an undesired stiff roll rate in the rear.

That can be an issue which is why you need to replace the front spring eyes with a pivot device and put soft durometer bushings in the shackles. This reduces the springs ability to act as a roll resistant device and instead puts that function on the lateral locating device. Failure to allow the springs to pivot will produce binding as the basic flat design of a leaf naturally resist twisting produced by body roll. Similarly, a watts is a better locating device, but its physical layout in relationship to other items in the area - axle housing, tanks, exhaust, etc, may result in compromised layouts that do not allow it to work as effectively as a panhard. Every chassis is different so review carefully. FWIW, the '70 AAR Cudas ran panhards, the Dodge Challenger TAs ran watts. The Cudas outqualified the Challengers early in the season until the Dodges swapped over to Panhards. Granted, development time on those chassis was limited and a one year only deal, so perhaps in time they could have made the watts work better. However, sometimes the better theory doesn't always produce the best results in the middle of the battle.

First, let me apologize for using the term "missing the point". I think that was inflammatory and that's now how I meant it; I only meant to add information to the already good information you provided.

Clint, thanks and likewise. Actually, after reading your post above, I believe you and I agree on our points even if appears we don't. I will say that leaf spring design layouts can be quite restraining and depending on the effort the OEM put into that design, can be a decent starting point or a real pain in the butt to work around.

I'd certainly recommend reading Afco's analysis of leaf spring layouts to any of the thread followers in here so they can better understand some of the dynamics of a leaf set up. It is not the end all of leaf design, but it does hit some key points. http://www.afcoracing.com/tech_pages/leaf.shtml

[Smoker03]

The caltracs work really well, but my question is will they keep the suspension from binding and still let it handle? I would use the fays2 watts link over a panhard