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Re: Leaf spring vodoo, the black hole of information
[Re: ThermoQuad]
#311479
05/08/09 08:41 AM
05/08/09 08:41 AM
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Joined: Mar 2005
Posts: 862
Iowa State fan
kilroy
super stock
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super stock
Joined: Mar 2005
Posts: 862
Iowa State fan
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Can you give a description and tools you used to measure your spring rate. I think I have an idea how but I would like to hear your method.
1973 Charger, former SE, former auto
I'm not trying to be difficult, it comes naturally....
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Re: Leaf spring vodoo, the black hole of information
[Re: kilroy]
#311482
05/08/09 12:05 PM
05/08/09 12:05 PM
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Joined: Jan 2003
Posts: 5,395
Pikes Peak Country
TC@HP2
master
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master
Joined: Jan 2003
Posts: 5,395
Pikes Peak Country
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Quick and easy means of measure is to simply invert the spring pack, stand on it, and have some one measure the deflection. Divide your weight by the amount of deflection, there is a reasonable approximation of spring rate.
Accurately determining the rear springs rates are always a little voodoo as very few places know their rates and your going to have to experiment to get them nailed down. Adding and subracting leaves is a bit of work to do repeatedly.
Also, the weight distribution of the car is a big factor in what rear springs you'll want. Weight distribution impacts the roll resistance need front to rear to balance the car.
In my car, the change from a 56% front weight bias to a 51% front weight bias changes the rear spring rate needed from 120# to 175#. That change could be as simple as a fiberglass hood, fenders, and bumper replacing the stock steel units. Get further into it with aluminum engine parts, engine set back, or relocated components and you may have to refigure your whole suspension set up.
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Re: Leaf spring vodoo, the black hole of information
[Re: kilroy]
#311483
05/08/09 12:05 PM
05/08/09 12:05 PM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
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Quote:
Can you give a description and tools you used to measure your spring rate. I think I have an idea how but I would like to hear your method.
easiest way to do it? put spring on ground upside down, probably on a scrap of plywood or something that has grease where it can slide (leaf gets longer as it's compressed) measure height. put known weight on it. remeasure height. if you want a little better apparatus, you could build something to bolt the spring eye to on one end, and a shackle on the other. conversely, you could probably take an old bathroom scale, put it on top of a chunk of 3/4" plywood, or a chunk of 2x12, etc. put a chunk of 2x8 or so on top if it about 1' long. place it on your floor jack. with the car up in the air, and the jack stands under the frame, not under the axle, lift under the shock plate with the jack/scale assy. a known distance (say, 1"-2") record the scale reading. divide by the distance you lifted. that is the spring rate of the spring in lb/in.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: Leaf spring vodoo, the black hole of information
[Re: patrick]
#311484
05/08/09 12:12 PM
05/08/09 12:12 PM
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Joined: Jan 2003
Posts: 27,490
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,490
So Cal
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Quote:
Quote:
Can you give a description and tools you used to measure your spring rate. I think I have an idea how but I would like to hear your method.
easiest way to do it? put spring on ground upside down, probably on a scrap of plywood or something that has grease where it can slide (leaf gets longer as it's compressed) measure height. put known weight on it. remeasure height. if you want a little better apparatus, you could build something to bolt the spring eye to on one end, and a shackle on the other. conversely, you could probably take an old bathroom scale, put it on top of a chunk of 3/4" plywood, or a chunk of 2x12, etc. put a chunk of 2x8 or so on top if it about 1' long. place it on your floor jack. with the car up in the air, and the jack stands under the frame, not under the axle, lift under the shock plate with the jack/scale assy. a known distance (say, 1"-2") record the scale reading. divide by the distance you lifted. that is the spring rate of the spring in lb/in.
Wonder how accurate that method is? I'm not doubting it, just wonder how close the accuracy is.
We rate leaf springs for our circle track car on a Longacre leaf spring rating machine. Like a spring rater, but with long arms to fixture the leaf.
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Re: Leaf spring vodoo, the black hole of information
[Re: autoxcuda]
#311487
05/08/09 04:05 PM
05/08/09 04:05 PM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
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Quote:
Quote:
Quote:
Can you give a description and tools you used to measure your spring rate. I think I have an idea how but I would like to hear your method.
easiest way to do it? put spring on ground upside down, probably on a scrap of plywood or something that has grease where it can slide (leaf gets longer as it's compressed) measure height. put known weight on it. remeasure height. if you want a little better apparatus, you could build something to bolt the spring eye to on one end, and a shackle on the other. conversely, you could probably take an old bathroom scale, put it on top of a chunk of 3/4" plywood, or a chunk of 2x12, etc. put a chunk of 2x8 or so on top if it about 1' long. place it on your floor jack. with the car up in the air, and the jack stands under the frame, not under the axle, lift under the shock plate with the jack/scale assy. a known distance (say, 1"-2") record the scale reading. divide by the distance you lifted. that is the spring rate of the spring in lb/in.
Wonder how accurate that method is? I'm not doubting it, just wonder how close the accuracy is.
We rate leaf springs for our circle track car on a Longacre leaf spring rating machine. Like a spring rater, but with long arms to fixture the leaf.
I don't see why it would be any less accurate, unless there's excessive sliding friction as the spring flattens out. If you build a fixture to use the front spring eye and a shackle, or just an axle with a couple wheels on the rear of the spring to minimize friction, it should be just as accurate.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: Leaf spring vodoo, the black hole of information
[Re: patrick]
#311488
05/08/09 04:25 PM
05/08/09 04:25 PM
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Joined: Dec 2006
Posts: 3,533
Indiana
Fury Fan
master
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master
Joined: Dec 2006
Posts: 3,533
Indiana
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I'd bet that the wheels off the 'small size' floor jack would be just about perfect for a home-brewed test like this. Easily returned to their original duty, too. 
Parts I seek:
driver doorpanel, 65 Sport Fury, prefer black, needs to be 7-8 on 10 scale, might buy set
16" x 6" Dodge truck wheel(s), from early 70s?, takes 9" dogdish - need for a research job so cheaper is better.
69-73 C-body caliper brackets and/or splashields
Send a PM.
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Re: Leaf spring vodoo, the black hole of information
[Re: Ply72rr]
#311489
05/08/09 05:06 PM
05/08/09 05:06 PM
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Joined: Jan 2003
Posts: 5,395
Pikes Peak Country
TC@HP2
master
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master
Joined: Jan 2003
Posts: 5,395
Pikes Peak Country
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Quote:
I remember reading a story about XV Engineering in one of the magazines and the XV guy said the torsion bars were too weak on old mopars compared to the leaf springs.The article gave me the impression that our cars need stronger torsion bars,thicker sway bars,and chassis stiffening. Maybe you road race guys can tell me if stronger leaf springs are really needed. I want to improve the handling of my charger when I redo the steering/suspension. 
All depends on where the weight is. More weight forward, less rear spring. More weight rearward, more rear spring. Also, sway bars count in the roll rate as well, so bigger sway bars can allow lighter springs.
BTW, those big 1" axle hung rear sways bars are only nominally more roll resistant the the stock .75 rear bars. I seem to recall the last time I ran the numbers, the 1" bar was only 10# more resistance because of its mounting points.
I was pondering the rear rate question last month on one of my cars, so I made a calculator that can figure rear springs rates. It's got plug ins for the t-bars, front and rear s-bars, roll couple, and weight distribution. Put in the numbers and it cranks out a leaf spring rate. It isn't spot on for perfection, but it will get the car closer to neuteral than guessing. I haven't had a chance to go thrash the car with it to verify how close it is. Tom, if you want, I can run some numbers on your old and new combo and see how they compare to your on track experience.
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Re: Leaf spring vodoo, the black hole of information
[Re: 73cudaproject]
#311492
05/08/09 09:35 PM
05/08/09 09:35 PM
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Joined: Jan 2003
Posts: 27,490
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,490
So Cal
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Quote:
Last week at a 1/2 price sale at a Salvation Army store my son bought a Petersen's "Basic Chassis, Suspension & Brakes" book from 1971 which has a very interesting section with all types of tips and pictures from Dick Landy. It even has pictures of items used, built and sold by Sox and Martin. Lots of info on springs, chassis, and items that maybe we take for granted today. If you can find it I recommend buying a copy.
I have it, but I think the old Mike Martin "Mopar Suspensions" book is much much better for handling info.
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Re: Leaf spring vodoo, the black hole of information
[Re: dirtybee]
#311494
05/08/09 11:36 PM
05/08/09 11:36 PM
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Joined: Jan 2003
Posts: 27,490
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,490
So Cal
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Quote:
could one just add weights to the trunk of a car on level ground and measure 'till the car drops one inch and divide by 2?
In theory yes, but the front rubber bushing twists and give resistance. And even with polys there is resistance. Would not give you the right or very consistant and repeatable numbers.
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Re: Leaf spring vodoo, the black hole of information
[Re: Lefty]
#311496
05/09/09 07:03 AM
05/09/09 07:03 AM
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Joined: Aug 2003
Posts: 2,474
Answering the call of the wild
ThermoQuad
OP
top fuel
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OP
top fuel
Joined: Aug 2003
Posts: 2,474
Answering the call of the wild
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Being that I have a street car that gets driven on the track I am trying to keep my approach simple as well as cost effective. I have not scaled the 4 corners...yet... It does weigh 3250 without driver as it's been on a rice & tuner diet...  I do know that based on pictures of my car at speed as well as feedback from others-I get a lot of good feedback because they are amazed at how well the old iron handles and goes like the devil- that more rear spring was required, but not a whole lot more. So I used the low buck approach knowing the results would be an improvement. Now that I know where I started and where I am at. I will probably leave the car the way it is and just enjoy the ride. I have new brake material compounds this year front and rear so it is going to be good time in the turns for sure. Tony thanks for your insightful input as always and I will take you up on your calculations offer later in the season. Mr Angry is running his Charger at Glen in Oct, so I may take a 2nd swipe at the track at that event if the $$$budget allows.
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I've heard there are people at our local fairgrounds dirt track (Watsonville Speedway) who do it for a fee on race night. I've been wanting to go watch the races and find out. 
