Leaf spring question

[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

[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]

So which leaf springs would work best for me? I go mostly straight line racing with the Blazer, but do street drive it to and from work,cruise-in's, etc... The slapper bars are getting kind of old and I'd like to drop the ride height a little more with a frame notch and maybe 4" blocks or a leaf spring relocation.

Later on I will be doing a G-machine build up on the '77 Pontiac and will need to do leaf springs there too.

[jaybee]

"You have to have some arch in the spring for it to have any traction."

Please elaborate, your input has been very instructive!

[68BNUT]

Good Thread Keep the good info coming. Id like to add a question though I noticed someone saying they had 600# rear springs? That seems like alot of rear spring for a street drivin car, What would be a good spring rate to look at for a 68 Camaro wanting to do some spirited grocery getting with possibly some open track day usage? I have 650# front springs.

[chicane67]

"You have to have some arch in the spring for it to have any traction." Please elaborate

I follow the Guldstrand and Smith theroy:

Leaf springs are generally "non-linear" or "progressive' in rate. They can however be operated in a "linear" or "constant" rate. The idea is to have leaf springs that compress to a certain amount and then are only used in a certain range of deflection, for example, 2.5 to 3" of travel. This range of travel and compresion can be related and the springs reaction can then be predictable. But if that spring is overloaded, its rating will go up drastically and change the predictability of handling.

One major associated problem that is inherent in leaf springs is "roll steer". What this means, is that as the car rolls and compresses the spring on the right side, for example, the arch is taken out of the spring and the spring grows in length. Depending on where along the spring the rear end housing is mounted, the right rear tire is either pushed ahead or pulled behind its proper centerline by the leaf spring growing in length and this steers the rear end slightly. But.... you can make this work for you as well.

Now here is what leads to your answer your question Slow. The arch of the leaf spring is what determines how weight being placed on it by body roll is divided by between lateral force and downward force. A spring that is flat, or very little to no arch, creates a very loose condition because body roll is being expended as lateral acceleration at the tire contact patch. More arch in the spring keeps the rear end glued to the track because there is more down pressure on the spring.

Id like to add a question though I noticed someone saying they had 600# rear springs? That seems like alot of rear spring for a street drivin car, What would be a good spring rate to look at for a 68 Camaro wanting to do some spirited grocery getting with possibly some open track day usage? I have 650# front springs.

600lb rear springs would only be used in a mid or rear engine chassis. It is not uncommon to see rates like this in, say, a Porsche 911 type rear engine or an Acura NSX mid engine. The fronts however will be much less.... actually about half of that.

In my 67, I run a 720 front and a 320 rear. Most say that is obserd, but I also have about 16 years in tuning the chassis.... and that is what this chassis wants and is what suits my driving style. I built the base chassis while working for Guldstrand, so ole' Richard was there to look over my shoulder and steer me in the right direction and schooling me along the way, making sure I wasnt doing somekinda no brainer.

To recommend spring rates is kinda tricky. There is a lot of information that has to be shared to get them right. Afterall, if you are going to spend the moola to build a set of custom springs, you wanna get them right the first time around. Chassis mods, battery relocation, body panel change, engine type and material of construction, wheel and tire package, front suspension modifications and parts being used, etc.. etc.. etc.

But in general, with a 650lb frount spring, you are looking at a spring around 200 to 250 lbs.

[jaybee]

My potential spring supplier can't supply me with a spring rate, but recommends removing the shortest leaf if their recommended spring proves to be too stiff. It's a 5 leaf spring. Is this an acceptable approach?

[CarlC]

If the spring manufacturer can't supply the rate, what qualifies them to be able to make a performance spring? He's making you guess, and that's not exactly scientific.

This is why it's usually not inexpensive to have really good parts made, no matter what they are. However, there was a group purchase several years ago at Team Camaro where they had Bett's Spring make a special 240#/in spring. Someone in here had a hand in that one . The price was very reasonable at the time, somewhere around $250. From reports, they work very well.

Then the question becomes: Is the price of a custom spring worth the money? To me, that depends on what you want to do with the car. If it's a cruiser and will only see an open track day once or twice in it life, an off the shelf spring from Hotchkis, GW, or Guldstrand will work fine. If you want to push the car hard, it's worth every cent. Though mine is not a traditional setup, the extra money spent not only worked at the track, it made for a better street setup as well.

The potential performance gain from spending $2K getting the front suspension dialed cannot be realized if the rear suspension is cheaped out. It's a suspension system and should be viewed as such for maximum performance.

[chicane67]

I would really need to see how the spring stack is to make that determination. If you are looking to control wheel hop, brake axle tramp and dial in the ride height.... I dont think they will be able to deliver at all, if only a few of those attributes. How much are they asking for the spring ??

I can design a spring, like I did for the Bett's group purchase at Team Camaro, or refer you to my builder that will build it to spec. I have already done the "rate to build" in my spring design, so it make it pretty easy on this end. It will also include changes for rate, ride height, wheel hop and axle tramp. The spring design basically has a built in traction bar.... in the leaf stack itself. So there will be nothing hanging down underneath the spring, nor does it require anything to be bolted to it to function. It is the ultimate sleeper spring.

Mind you that the Bett's spring deal was a single design that covered a group purchase and was initially set-up for the one who started the purchase. The spring however, covered a group of cars that were very similar in power and build..... so that peticular spring was not made for each chassis, like I normally do. But, since these cats were after something that was much better than the main stream, off the shelf type leaf, it worked out for all. That and the fact of the group purchase, made the price real attractive. $250.00 for this type of spring is a smokin deal.........

[harshman]

I would really need to see how the spring stack is to make that determination. If you are looking to control wheel hop, brake axle tramp and dial in the ride height.... I dont think they will be able to deliver at all, if only a few of those attributes. How much are they asking for the spring ??

I can design a spring, like I did for the Bett's group purchase at Team Camaro, or refer you to my builder that will build it to spec. I have already done the "rate to build" in my spring design, so it make it pretty easy on this end. It will also include changes for rate, ride height, wheel hop and axle tramp. The spring design basically has a built in traction bar.... in the leaf stack itself. So there will be nothing hanging down underneath the spring, nor does it require anything to be bolted to it to function. It is the ultimate sleeper spring.

Mind you that the Bett's spring deal was a single design that covered a group purchase and was initially set-up for the one who started the purchase. The spring however, covered a group of cars that were very similar in power and build..... so that peticular spring was not made for each chassis, like I normally do. But, since these cats were after something that was much better than the main stream, off the shelf type leaf, it worked out for all. That and the fact of the group purchase, made the price real attractive. $250.00 for this type of spring is a smokin deal.........

since most of us are looking at the 500 hp mark as the goal and performance is our preference, how 'bout another GP with Bett's. I think there is one in Phoenix. I'd be up for one that is designed by you for $250.

[CarlC]

The Good, The Bad, and The Ugly:

http://www.camaros.net/forums/showth...ighlight=betts

http://www.camaros.net/forums/showth...ighlight=betts

http://www.camaros.net/forums/showth...ighlight=betts

http://www.camaros.net/forums/showth...ighlight=betts

With a few minor changes added it will still be a great deal even if only one pair is ordered.

[jaybee]

It's a fantastic solution...if you have a Camaro. Unfortunately I don't. I'm trying to get the most possible advantage out of a 57 Chevy on the street without going to a custom chassis or other "exotic" solutions. I'm not aware of a spring for these cars from GW, Gulstrand, or any of the names that are prominent in PT circles. For that reason I particularly appreciate your patient explanations. The spring I have my eye on is from Posies...a Street Rod manufacturer. As far as I know it hasn't been tested as a true performance part. It has reversed eyes and is dearched to provide a total drop of 3", with plastic buttons under the leaf ends to reduce friction. In terms of material size and leaf count it duplicates an original, factory spring and therefore presumably would be close to factory spring rate. Is it the best solution? Beats me, that's what I'm trying to figure out. Hope I'm not driving you nuts with this topic, I've found it extremely informative.

[chicane67]

Never fear Jaybee....... the same can be done four your project as well.

[astroracer]

Are you planning any chassis changes or are you looking to simply bolt in a new spring? If there is a narrowing planned or you are moving the springs in any way you can easily build the rear suspension around a Camaro leaf spring. That would give you endless options and may be the way to go...
I am considering this for my Bad ast project as there just isn't a lot of "options" for an Astro van either...
Mark

[jaybee]

OK, now that I've had a little time to read the material and dive into all the links I believe I'm beginning to understand. Particularly useful were the pictures and plans of the custom spring. What I see there is a variation on the Mopar Super Stock drag spring from the 60s in which an extended leaf is used to control spring wrap. The 2nd leaf has that 1/4 wrap of the spring eye to ensure that it's applying force directly into the eye instead of just transferring it to the main leaf, and the 1st and 2nd leaves are banded shortly behind the front eye to better control braking torque, right? After that it should be just a matter of good bushings and the right shock settings, no cheapos from AutoZone.

As far as chassis changes I plan to keep it pretty mild. Relocating the springs would be a lot of work for a car that will already fit 275s, to get full utility out of a spring pocket kit would require tubs. Then there's virtually no place to put the exhaust.

I do plan on putting a shock absorber crossmember into the car. The floors can flex, the crossmember improves the ride slightly by isolating shock inputs to the frame instead of the body, and a welded-in crossmember will make the frame more solid in the kickup area. Room between the axle and fuel tank makes it tough to get into staggered shocks & such, and I don't know that they really accomplish that much anyway. My plan is to weld in an X member and possibly box the rear crossmember. The stock frame is built from rugged stuff but is seriously lacking in rigidity. All the strength is in the front crossmember and the rails just sort of trail out behind with only an unboxed rear crossmember right in front of the back bumper.

[chicane67]

What I see there is a variation on the Mopar Super Stock drag spring from the 60s in which an extended leaf is used to control spring wrap. The 2nd leaf has that 1/4 wrap of the spring eye to ensure that it's applying force directly into the eye instead of just transferring it to the main leaf, and the 1st and 2nd leaves are banded shortly behind the front eye to better control braking torque, right?

Well.... kinda. The spring you are talking about is the Tri-City Competition drag spring that was originally designed and used by D ick Landy, the Godfather of drag racing for Mopar. The funny thing is.... my spring builder is the very same cat that built that spring for D ick Landy for the past 45+ years. All these guys were local to me in my home town area.... so I got the skinny from them and got to share ideas on what I was after.

The difference in the two spring design's is, on my design, the rear of the spring pack is where the brake torque is being controlled..... well, I'll say about 95% of it anyway. If you put it all in the forward part of the leaf like the Tri-City spring, it becomes too stiff for road use and it kills the ride.

Another point. I dont use staggered shock on my 67 and its not necessary to run a staggered shock set-up. The springs locate the suspension and control wheel hop so well, that the issue driving the need for staggered shocks is a thing of the past. GM tried to prove that what they devised as a fix, to the early wheel hop problem by staggering the rear shocks, was a huge farse. Guldstrand and Penske proved that the intial GM spring design was the issue. But back then, the "Piggins" group didnt want this getting out to the main stream and giving up a discernable edge over the competition. The idea never went production in passenger car chassis.

Thank God those old guys were smart.