Leaf spring question

[jaybee]

OK, I've spent some hours going through posts and searching topics. I've picked up that a leaf spring suspension can be tuned to work well on the street with the right spring rate, shocks, and MAYBE a mild sway bar to fine tune the balance. Sounds also like adding a panhard or watts link is wasted effort for a street car (please feel free to correct me if I have any of this wrong). Also that there's a certain amount of disagreement over using Delalum or Polygraphite bushings

I'm also getting the impression that traction bars such as CalTracs or slapper bars at best have no impact on handling and at worst could be pretty detrimental, depending largely on preload. How about simple underride or override traction bars such as on early Shelby Mustangs?

[wendell]

Over rider bars are frequently used on gt350s for vintage racing. They are effective. That said, the amount of developement and tuning that goes into them is staggering. Trust me, there's a LOT more to it than meets the eye. The motivation behind all this inovation is the 9.5" spec tire. The most sucessful set ups involve spring loaded links and or biscuits to manage the forces.(think dirt late model). For a street car I wouldn't even consider it. A lateral locating device would have a larger possive impact on performance and be a lot easier to develope.

Regardless, a well speced spring driven on the street will need neither traction bars nor a lateral locator. KIS.

[jaybee]

Sounds like a whole bunch of track testing. I keep reading that the right springs are all you need. How do I recognize the right springs?

[astroracer]

It really depends on the end usage of the car. If it is a street car what is your performance goal? Straight ahead? Cornering? If both, a good set of handling springs from Hotchkiss or Gulstrand is probably all you'll need. There are so many variables on the street how do you determine if one spring is worth 2 tenths on the drive to the store over another set? Looking at it from a street aspect the stock springs may work better as they will probably be less harsh then a performance version and provide less "skip" going around lumpy-bumpy gravelly corners.
Something else to think about is street driving versus track driving. How good does your suspension have to be to get you around a big sweeper entrance ramp to the expressway as compared to hot lapping around a race track. A street car will NEVER get pushed to it's limits on the street as compared to a track only car on the track.
I did a lot of research when I was conceptualizing my Bad Ast Project and I finally realized this is a STREET oriented vehicle. I didn't have to spend thousands of dollars on a race oriented suspension to make the van handle exceptionally well on the street. Granted it probably won't be a barn burner going around a track but that is a moot point when it boils down to street versus track time... It will see much more street time and that is where I need it to work...
Mark

[chicane67]

Sounds like a whole bunch of track testing. I keep reading that the right springs are all you need. How do I recognize the right springs?

By their design and construction. There is more to spring science than meets the eye..... and there are many factors that need to go into the 'correct' spring build. There are very few individuals that have taken the time to learn, understand and build spring for exactly what is in question here.

I got the majority of my experience while working for the godfather of F-body roadrace/autocross/ProTouring. **** Guldstrand. His "FIA" spring designs are still packed full of surprises. I since then, have built several designs from a simple street spring to a full blown 24hr Daytona roadrace spring. And all I really have to say is... that a properly designed spring in a hotchkis type rear suspension does not need and or require a stay-bar or any type of forward location device, ie, a traction bar/CalTrac/under/overbar.

The only thing that traction bars are need for are for IC location because of soft, weak and poorly designed leafsprings. A correctly designed spring will also take into consideration IC location, braking force axle tramp, wheel hop and keeping the chassis off of the bump stops. We'll leave the subject of spring, frame eye bushings and shackels out of it right now..... because there is really only one solution to this issue.

Jaybee's understanding is just about point on. The truth to most of this is really in the shock and spring package combined and unfortunately, on the shock side of this, it comes down to an expensive shock set-up. Which at a minimum, means a double adjustable. In reality, a bypass triple. But lets get out of the stratosphere for now and talk springs.

[Mean 69]

I am not a leaf spring kind of guy due to the products we are marketing, but I can also state, without any doubt, that leafs can work. If done well. And, as some form of fate may have it, THE two dudes that I would refer anyone with a leaf question to, are both in this thread. They both happen to be good friends of mine though they have never met each other, both highly intelligent, and could dominate the leaf world if working together. Bar none.

Wendell (Jensen), meet Chicane (Tom). And vice versa.
\Mark

P.S: Wheel Hop? Under acceleration, or braking? Full throttle, part throttle? Details please!

[steemin]

P.S: Wheel Hop? Under acceleration, or braking? Full throttle, part throttle? Details please![/quote]

Thanks for the response..
In attempting to launch the car hard from a dead stop or a roll and even when I try to really nail 2nd gear I get zero tire spin.
All I get is wheel hop...
I obviously avoid doing this as it is brutal on the rear end.
FYI the car is a 5 speed with a 3.89 Ford 9" rear end
(2.95 1st gear) and has 382 RWHP. It also has a Meirer racing sub frame connectors welded in. For tires I have Bridgestone Potenza Pole Position 245X40X18's. I have had the pinion angles checked and I was told that they are okay..
I am not sure but it is possible that my leaf springs are old and
tired and are the cause of my problems
Scott

[wendell]

That's a good description of the problem. Does it hop with out the under riders? What type of bushing material is used in the spring eyes and in the bars?

[chicane67]

I am not sure but it is possible that my leaf springs are old and tired and are the cause of my problems

Just some thoughts..... One factor to the problem could be the OE design and the age of the steel. Is it the only problem ?? Well, I dont think so. Lets cover a few simple insights to this issue......

First, I believe you are running under-rider bars with your OE design leafs and they are showing their age ?? Well, I believe that the biggest and most appearent problem that we are looking at, is geometric. The under-rider bars, being fixed mount with solid links, move in a known and fixed geometric arch. The leaf springs however, move in an increasing radius when compressed and I bet you can guess what the problem is. Yup, the suspension goes into bind.... and that is just the beginning.

When you have the solid link underneath the spring, and as the suspension compresses, it not only drives the pinion angle positive but it also loads the leaf to the point of induceing wheel hop. The wheel hop comes from the spring being loaded into an "S" shape from the pinion angle being driven upward (due to a weak forward leaf stack) and when it reaches it mechanical limits, it unloads the spring energy and snaps back to its unloaded self. This violent state basically loads and unloads the leaf spring evertime it transitions from high traction until it reaches its limits and unloads... over and over again. This is your basic wheel hop.

HOW "WHEEL HOP" OCCURS
Rear Axle Housing Rotation Without Traction Control:

When horsepower is suddenly delivered to the differential, whether from a clutch or a torque converter, the pinion attempts to "climb" the ring gear. This sudden shock of torque causes the entire rear axle housing to rotate backwards in a counter-clockwise direction. This causes the springs to distort, resulting in severe driveshaft/U-joint misalignment.

Spring Reaction Unloads Suspension,
Causing "Wheel-Hop":

The axle housing is allowed to continue its rotation until it meets resistance from the suspension/springs, which then try to "snap" the housing back to its original position. As power continues to the differential, the housing is once again allowed to rotate back against the springs. This action/reaction of the suspension, commonly known as "wheel hop," continues much like a tug-of-war. Instead of launching your car forward, you sit there bouncing around and spinning your wheels.

A driving concept behind a link system is that you can adjust the pinion angle and locate the IC. But in a hotchkis type suspension, without a third/four (upper) link, you really dont get to control this, because the leaf suspension is dynamic. With only having a solid link on the lower and it moving in a fixed geometry, along with the leaf spring changing is arch as it is compressed, is something that is not controlled. For the linky types here, it is basically the same as having an upper bar that is too long and/or having that upper bar's forward mount too high, relative to its rear mount.

3. Now you have the rear axle centerline. (1) If "the center line of the front spring eye level with the centerline of the main spring leaf" is correct, the front spring eye needs to be at the height of the spring pads on the axle. The sping selected needs to be rated and arched such that this relationship is preserved at ride height.
4. If that doesn't give the visual stance you're looking for, or you wish to lower the center of gravity, (2) the shackles and front eye need to be moved upward. If that provides insufficient wheel travel you're potentially into major surgery.

1.) This isnt really the correct approach. To pull this off you would have to either have a very flat forward spring with no arch that it would make for an increase in rear roll stiffness so much that it would make the chassis naturally loose. Or, it will lower the ride height from having an increse in spring free arch (with the limitations being right up to the shackle going into the rear frame rail). You have to have some arch in the spring for it to have any traction.

2.) Playing around with the forward mount can be real tricky. As soon as you move the forward or rear mount, you change the RCH.

[Slow Ride]

By their design and construction. There is more to spring science than meets the eye..... and there are many factors that need to go into the 'correct' spring build. There are very few individuals that have taken the time to learn, understand and build spring for exactly what is in question here.

I got the majority of my experience while working for the godfather of F-body roadrace/autocross/ProTouring. **** Guldstrand. His "FIA" spring designs are still packed full of surprises. I since then, have built several designs from a simple street spring to a full blown 24hr Daytona roadrace spring. And all I really have to say is... that a properly designed spring in a hotchkis type rear suspension does not need and or require a stay-bar or any type of forward location device, ie, a traction bar/CalTrac/under/overbar.

The only thing that traction bars are need for are for IC location because of soft, weak and poorly designed leafsprings. A correctly designed spring will also take into consideration IC location, braking force axle tramp, wheel hop and keeping the chassis off of the bump stops. We'll leave the subject of spring, frame eye bushings and shackels out of it right now..... because there is really only one solution to this issue.

Jaybee's understanding is just about point on. The truth to most of this is really in the shock and spring package combined and unfortunately, on the shock side of this, it comes down to an expensive shock set-up. Which at a minimum, means a double adjustable. In reality, a bypass triple. But lets get out of the stratosphere for now and talk springs.

I need you to design me some leaf springs for my Blazer. I broke the stock ones because of axle wrap, so now I run traction bars with beltech leaf springs, but would love to gain back the ground clearance and still have the thing launch correctly. I don't even have the good motor built yet and I'm breaking stuff.

As you can see things are a bit tight under there with 315/60's

http://i56.photobucket.com/albums/g1...4/DSCN0361.jpg

http://i56.photobucket.com/albums/g1...4/DSCN0353.jpg

[patriot68]

how do the dse 3" drop springs compare to hotchkis and others??

[Norwoodx55]

We'll leave the subject of spring, frame eye bushings and shackels out of it right now..... because there is really only one solution to this issue.

Well I am ready for this part now. The suspense is killing me.

[wendell]

The word on the street is that Chicane's brain is big. I'd definately differ to him on all things leaf. That said, I made this one car go pretty good one time...

[steemin]

I am subscribing to this thread as I am having issues with my leaf spring rear end.
My car will primarily be street driven with an occasional trip to the drag strip.
The car is a 65 Mustang Fastback.
I have red Koni shocks,4 leaf springs and Shelby under rider traction bars. My car will not spin the tires.
I just get an insane amount of wheel hop


So I am looking for answers as well.
Scott

[jaybee]

My understanding of springs and shocks is built on what I learned from dirt bikes, so the philosophy for a fast road car could easily be different. In that arena the target spring would be just strong enough to keep the suspension from bottoming on the largest bumps the bike is going to encounter. Shocks are soft on compression to let the springs work and stronger on rebound to keep from overshooting ride height. Too much rebound damping is to be avoided as the suspension will pack down over washboard or repeated bumps. Shock valving has to be sophisticated enough to provide correct response on large wheel motions while at the same time remaining supple on stutter bumps, without which the machine will get skittish as the wheels lose adhesion.

First of all, does ANY of this relate at all to a hot street car, second, it tells me absolutely nothing about the correct specs and construction of a leaf spring suspension.

[jaybee]

I don't know if anyone builds a true performance spring for a 57 Chevy. Before discovering this site I had pretty well decided on a 3" drop Posies Super Slide spring which comes with moly/nylon buttons for reduced friction and Polygraphite bushings. I'll admit to knowing absolutely nothing about controlling spring behavior through design beyond the old MOPAR Super Stock springs of the early 60s which used an extra, partial leaf to control spring wrap under acceleration. I'm eager to learn and grateful for your assistance, however, please school me!

[jaybee]

"The truth to most of this is really in the shock and spring package combined and unfortunately, on the shock side of this, it comes down to an expensive shock set-up."

Sometimes you spend the money one place to save it someplace else. Good shocks cost money, but so do CalTracs or good-quality slapper bars.

[Bandit]

I agree with astroracer's comments: "It really depends on the end usage of the car. If it is a street car what is your performance goal? Straight ahead? Cornering? If both, a good set of handling springs from Hotchkiss or Gulstrand is probably all you'll need."
In my case I wanted a great all-around street setup, that handles flat in the twisties.
I have a Hotchkis Total Vehicle (TVS) setup, 600lb 2" lowering springs front, 1.5" lowered rear, on my '80 TA and I can say that this kit has met all of my expectations and then some, and it's not really expensive (about $1400 with shocks). I wanted to maintain the stock configuration and mounting points, which the kit does (no crazy fabrication), except for a different rear swaybar setup (at least on my car). I used Bilstein shocks. The first thing I noticed was that the suspension is QUICK! Meaning that at high speed on the highway, when I go over a slight inclination, there is no more of that scary "floating" sensation that forces you to slow down, the car just lifts, then quickly plants itself back down, with no hint of bouncing afterwards. The other thing is that it is a noticeably rougher ride, but who cares, right? If we wanted a soft ride we would all drive '76 Buick Electras.
I will include a link to an excellent article that helped me alot when I was researching suspension options, some of you might know the author but I don't, anyway it is really well written and worth the read:

http://racingarticles.com/article_racing-9.html

The main thing I got from it was: pick one reputable company, and buy all of your parts from them as a system. That way, you know you are getting a good system that has already been proven to work; otherwise, there are just too many variables to piecing a system together from scratch, which could be a frustrating process.

Anyway, good luck with your selection. Sorry this post turned into a novel.

Paul
"If at first you don't succeed, get a bigger hammer"

[jaybee]

Don't worry about writing a novel, This has all been extremely interesting. One thing that stood out from the linked article was the phrase "the center line of the front spring eye level with the centerline of the main spring leaf." Now we're getting into geometry. What exactly is determined by this relationship, I'm guessing instant center? If so that could be a huge contributor to how the car behaves under power.

In that case it throws out the concept of determining stance with lowering springs. As I think that through it looks like chassis package would need to be determined as follows:
1. Determine what size FRONT tire you can run. You'd do that first because space for fronts is normally more restricted than rears.
2. Decide on a size split front to rear. That's the reason for step 1, so you don't unbalance the car with an enormous tire size difference.
3. Now you have the rear axle centerline. If "the center line of the front spring eye level with the centerline of the main spring leaf" is correct, the front spring eye needs to be at the height of the spring pads on the axle. The sping selected needs to be rated and arched such that this relationship is preserved at ride height.
4. If that doesn't give the visual stance you're looking for, or you wish to lower the center of gravity, the shackles and front eye need to be moved upward. If that provides insufficient wheel travel you're potentially into major surgery.

I have a feeling I've made this more complicated than it needs to be, but potentially correct setup could be anything from relatively simple to very complex. Looking at my own project the spring pads are several inches below the front spring eye. The car also has long shackles that will need to come off. It looks as if a set of stock-length shackles and a reversed-eye spring providing 3" drop total could be just about right.

[Bandit]

I wouldn't read too much into the writer's statements about front spring eye-canterline etc. "...having a spring shop make a set of springs with the rate you desire and that has the center line of the front spring eye level with the centerline of the main spring leaf" --I think his main point is simply that having a spring custom made, with a more gradual bend, is the best method of lowering the rear of the car.
I would think having custom springs made is not a very common thing for the average guy to do though--it sounds expensive. I think in my case, a spring like he describes would lower the rear of my car too much. When I installed my Hotchkis rear "lowering" springs, my rear ride height actually went up an inch or so, although my handling improved vastly. I think that was due to my old factory springs badly sagging and refusing to do their job anymore. In my case for everyday driving, I think a little extra ride height is a good tradeoff to not having tire rub with wide rear tires.

I follow your line of thought with starting with the biggest front tire/wheel combo you can fit, and choosing your rear wheel/tire to match: it's all about compromise though, and in my case I wasn't willing to give up a wide rear tire, so I have quite a bigger wheel in rear, 18 X 9-285/45, vs. 18 X 8 - 245/45 up front. With the bigger tire you need enough room for suspension travel of course, unless you have alot more bodywork done than I do.

That said, companies like Hotchkis and GW make packages that do everything pretty well, handling, launching from a stop, and decent ride quality. If you want to get even more serious in one area or lower the car way beyond stock, then you probably will have some major modifying to do. That's where custom-built subframes like those from fatman fabrications come in handy (so does lots of cash).


Paul