I've did a fair amount of internet searching this afternoon but just not finding a formula. The springs are the Speedway gasser springs, 31 inches long and rated at 400 lbs per inch, I understand that it takes 400 pounds to compress the spring one inch. I'm looking for the maximum load Rate for the springs. Some articles say there's a recommended "built in" deflection amount when rating springs, say 1 inch above and below resting height, other articles say the Rate changes the flatter it gets. Do you multiply the compressed inches until the spring is flat, say the spring has a 5 inch arch multiplied by the 400 lbs/per to get a total of 2,000 lbs and is that again multiplied by 2 because you have 2 springs ??? I can't find the white rabbit down this rabbit hole.
You may find something in Machinery Handbook, I remember seeling somathing years ago. To me you mite as well chase a Whistle Pig. But up side you are right in your adding; 2k each spring and 4k total. Another butt is that the first inch or two may be way less than 400 per inch as it takes some travel before all the leaves are working. So actual from when it starts to be 400 per inch to flat maybe closer to 3-1/2 or 4 travel or about 1500 each x 2. That is a lot of spring, you will feel every dime on the road. Go to u -tube and look up leaf spring manufacturing, you will see that each leaf has more arch than the next and the resulting arch of the spring has the fact that some leafs are not loaded at all but are unloaded.
Swade, all I can say is they are stiff and you probably know that... I have used them twice before on iron headed big block chevy's , one a 55 210 the other a Willy's. Setting one up now a 62 Falcon with an sbc. I have a fully built mock up sbc with a complete t350 in it and the springs may compress maybe an inch? Even with all 230 lbs of me on the core support it doesn't drop much more. I will probably remove a leaf or two. I know this isn't answering the total weight question.
Funny thing about the springs from speedway...when you get them with a kit, they describe how to figure out how many leaves to remove so they have a nice ride. In other words, the rate is adjustable, by removing leaves. 400 is the maximum, probably around 200 is the minimum with half the leaves removed, every other leaf. For a rough approximation, I think you have the right idea, spring rate in lb/in, times inches deflection at the center of the spring, times two springs.
I removed half of the springs, when I was running the formula with spring width x spring thickness x length it came out to I believe 229 lbs per inch. Again this got me thinking of how does this formula work because it doesn't know the length of the 2 springs under the main leaf which you're getting your length from. I used the 2 longest and the second shortest, I would think that would have to be a different load Rate than say the 3 longest leafs combination.
What complicates things is leaf springs are non-linear. They get stiffer with deflection. Spring rate should be measured at the rated load.
Finding the load rating for leaf springs can be difficult in the automotive world, much easier in the heavy truck side of things. The load rating (if it exists) is typically listed at ride height, not flat. Ideally you want the leaf spring to be just short of fully flat at full compression, which is typically 2g's, or 2 times the vehicles weight supported by that spring. So if your load rate is 400 lbs per inch, and there is 5 inches of compression from unloaded to flat. Ideally ride height would be at 2.5" of compression, and provide 1000 lb of load capacity. Another 2.5" more compression to flat, or hopefully the bump stop, would result in 2000 lbs or 2 g's at full compression. 5" of total suspension travel from full rebound to full jounce. I have tested hundreds of leaf springs to failure, it is always interesting when they finally pop. ]
As far as ride comfort, the shock angle has a lot to do with it. I wanted to stiffen the ride of my car in the back and added several leaves but gained very little until I moved my upper shock mounts to stand them up straighter. Gary
I have the Speedway springs on both of my gassers, and both are SBC engines. But my '39 Chev coupe weighs a hefty 3500 lbs. where my Austin weighs 2300 lbs. I'm only running the two longest leafs on the front of my Austin, but the full pack on my '39. Both ride about the same; firm, but not harsh.
A leaf spring is not variable rate. The rating does not increase by compression. If it takes X pounds to compress the spring one inch it takes 2X pounds to compress it two inches. It is linear to the point of break down. A coil spring on the other hand can be wound to be variable rate. More compression higher rate. This will not be what you normally buy for your coil overs. A straight wound coil spring will be linear like a leaf spring. The point of break down on a coil is called spring bind, the coils have no more travel. The point of break down on a leaf spring on the other hand can be more catastrophic. Breaking point on a leaf spring is normally considered when the arc no longer exists and the spring either reverses itself or it snaps. Determining spring rate requirements for a vehicle is not as simple as the vehicle weighs X pounds at Y wheel so it needs an X rated spring. You have to consider dead loads V live loads and take moment loads into consideration. That is why we have charts, most hot rodders are not well versed in structural engineering. None of this is much help but now it is out of my head and I have room for other stuff.
Notice when the spring is assembled that each leaf from the main on down to the shortest has more arch. This is what makes the spring have some kind of progression. Notice also that once the spring is assembled it has a certain amount of arch and then it is over loaded and the arch measured, it does become less.
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