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Old 10-12-2008, 10:50 PM   #1
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Coil vs. Leaf Springs Throwdown

This is two opinions about coil vs. leaf from Four Wheeler Magazine.

The Great Four Wheeler 4x4 Throwdown - Great Debates

Suspension: Coils Vs. Leaves


Opinion 1. Sprung On Coils, And Proud Of It!

Take a look around. The auto industry has already graduated from the high-friction horse-and-buggy technology of yesteryear. Abandoned for good reason, leaf-pack technology has almost completely disappeared in favor of the compact, precise, and better-riding coil spring of today. We dare you to find a new car that still has leaf springs under it from the factory. The pickings are slim if any. Sure, you will still find them in the back of trusty pickup trucks, but even those are a dying breed as demonstrated by the new configuration on the rear of the '09 Dodge Ram 1/2-ton pickup shown here.

The reason for this shift in technology is obvious. Coils weigh less. When it comes to new vehicle production, weight savings is a top priority. Coils are also now much simpler to manufacture than leaf springs, and they require less raw material to start with. The basic nature of a coil-sprung link-type suspension also eliminates that dreaded axlewrap. Just compare a Jeep YJ to the newer TJ or JK; coils have a lot to do with the Wrangler's improved performance.

The basic function of springs in a suspension system is to change mechanical motion into heat energy, and our centuries-old leaf-spring technology does that very well. However, when you consider the weight and the intense friction created by multiple layers of metal rubbing against each other as a leaf spring flexes, you have to wonder why this method is still in use today. Another place where coils have been proven over and over is in desert racing; when was the last time you noticed a set of leaf springs under a Trophy Truck? Bound for success, coils are the new gold standard.

-Robin Stover


Opinion 2. Leaf Springs: Simple, Functional.

The leaf spring has been the standard for suspension systems since the dawn of the automobile, and the mighty leaf isn't going anywhere anytime soon. Coil springs may be less expensive to produce when compared to a leaf spring, but that savings is offset by the fact that a coil-spring setup requires links to locate the axle. These links add cost and weight and require a fair amount of configuring and subsequent testing to work correctly. If they're not installed correctly, they can actually limit the steering radius because the tire will come in contact with links. The leaf spring, in all its glory, doesn't require any links because the spring locates the axle by itself. That's simplicity, and simplicity is good.

Another benefit to leaf springs is their strength and stability. If you drive a trail toy this probably is of no concern to you, but if you're a workin' Joe who uses his truck to tow and haul, it is of utmost importance. Look, there's a reason why 3/4- and 1-ton pickups don't have a coil-spring rear suspension. Leaf springs are stronger than a coil spring, they have more load-carrying capacity, and they also help reduce sway.

While we're on the subject of capacity, let's talk about ride quality because the misconception is that leaf springs can't offer a high capacity while providing a smooth ride. Hogwash. Clearly, the balance between the two is a tradeoff in any spring design, but a custom leaf-spring manufacturer can work with you to make springs for your rig that achieve an acceptable balance.

Let's talk wheel travel. Sure, we've all seen coil-sprung rigs that have incredible wheel travel. What did it take to get that? Well, it probably took gobs of time-consuming engineering, custom long-arm links that required relocation or custom fabbing of the link mounts, and expensive spherical rod ends or some kind of high-falutin' flexy joint. Sure, it probably impresses the heck out of their friends, and it's way prettier than a simple leaf-spring pack, but it takes lots more time and money. With the leaf spring, you don't have to deal with any of that. We've seen gut-wrenchingly simple leaf-spring setups that offer crazy axle flex. Bottom line: They're not perfect, but leaf springs offer a variety of benEFIts in a simple, cost-effective package.

-Ken Brubaker
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Old 10-12-2008, 11:59 PM   #2
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this is one of those subjects I have filed into the back of my mind to compare ride quality of my (coil) setup vs some of the other vans at the next get together.

Turning radius is also one of those things I think would be affected by the different suspension architecture.
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Old 10-14-2008, 11:08 AM   #3
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I've always been fond of some of the trick coil-spring set-ups I've seen on various off road vehicles, including some of the hardest of hard core rock crawlers. Some Jeeps too, and the SK system that Buji and others have looks awesome. But to me, this statement is what tells me I've got the right set-up on a slightly top heavy 5-ton van that's nearly 20-feet long:

Quote:
Leaf springs are stronger than a coil spring, they have more load-carrying capacity, and they also help reduce sway.
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Old 10-14-2008, 12:42 PM   #4
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But those two benefits really don't come into play on the front end, do they? I find my spring rate is plenty for the front end, and I don't know enough about suspension architecture to know if the difference would make any stability difference (on the front end).
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Old 10-14-2008, 09:02 PM   #5
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Remember the majority of 10 and 20 series Chevrolet trucks from 1967 to 1972 were shipped with a coil spring trailing arm rear suspension. They were kinda springy.
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Old 10-14-2008, 10:00 PM   #6
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Valid point on the front end Buji, and I'd be willing to bet your ride overall is probably a little less harsh too.
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Old 10-14-2008, 10:05 PM   #7
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On front ends, coils are situated much further apart than leafs. Leafs are on the frame rails. Coils are a good 8 inches per side wider and right on top of the knuckle. I think that makes a difference. Think about lifting weights. A wider grip gives you much more leverage and control.
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