Why are coil springs better than leaf springs?

Leaf Springs Vs. Coil Springs: Which Suspension System Is Better?

A suspension system is a system of springs, shock absorbers and linkages that connect a vehicle to its wheels and allows relative motion between the two. It is responsible for a vehicle’s handling and braking for safety. There are a variety of independent suspension systems; however in this blog we will only be comparing two types of Spring Suspension Systems; The Leaf Spring System and the Coil Spring System.

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What are Leaf Springs and Coils?

Well a leaf spring suspension is made of a series of relatively long strips of steel attached at both ends to a frame and suspending the axle in the middle. A leaf spring takes the form of a slender arc-shaped length of spring steel of rectangular cross-section.  Coil springs as the name suggests, look exactly like how one imagines a spring to look like. It sits on top of the axle or at the lower control arm and the chassis. A coil by definition is a mechanical device which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces.

Here’s a quick comparison of Leaf Springs with Coil Springs for the sake of debate:

Leaf Springs

Leaf spring suspensions are much simpler in terms of functionality as the axle is suspended by the spring, and does not require the arduous suspension geometry of the coil-spring set-up. Leaf springs are also much sturdier as compared to the coil springs. They are capable of handling much higher loads with less deflection than coils. Trucks with leaf springs are also easier to raise or lower.

The leaf springs’ simplicity is as much of a curse as a blessing. Since this spring is attached at fixed points on the chassis, it leaves a minuscule room for adjustability and customization of the suspension geometry. These springs also flex a great deal less than coil springs, resulting in a loss of wheel-to-ground contact under extreme conditions.

Coil Springs

Coil spring suspensions offer more range of suspension movement, and allow the user a wider tuning envelope through the suspension range than leaf springs. Practically all high performance applications use coil springs where possible and if the budget permits.

The two main drawbacks to a coil spring suspension are cost and load-bearing. Cost isn’t so much an issue if the vehicle is originally equipped with coil springs, however the retro-fits can be quite expensive and time consuming. Coils are not ordinarily preferred for very heavy vehicles, as the coil on axle setup isn’t remotely as stable or strong as a proper leaf spring.

Conclusion:

This brings us to a conclusion that each of these suspension systems have their applications unique to their functionality and are used accordingly! Leaf springs will usually do an acceptable job and prove themselves a durable choice in the case of heavy, industrial or budget-limited applications; However, there are a very few applications which will benefit from choosing a leaf spring over a coil spring when it’s a matter of performance.

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Leaf springs are treated like archaic tech, as they aren't found under any of the latest industry-leading performance cars, and are often used as a point of reference that shows how "dated" a particular design is. Even so, they're still prevalent on today's roadways and can still be found under some production-line-fresh vehicles.

The fact that they're still used in vehicles today makes it clear that the discussion of "leaf springs vs. coil springs" isn't as simple as it seems. Sure, coil springs are great, but leaf springs sticking around after all of these years surely means there are situations where the older way is superior. And if you're working with the same budget as the rest of us, you're not rolling on the latest and greatest suspension designs anyway, meaning it's worth learning a little more about the two.

Relax. We're not in for a massive info dump that'll overhaul your way of thinking. A brief overview of the basic differences between these two suspension types is all you need to get a grip on which is better when. 

Basic Spring Types

Springs have multiple jobs in suspension systems. For one, it supports the weight of the vehicle while allowing for up-and-down movement of the wheels. They absorb bumps and help compensate for uneven surfaces while working to retain the set geometry established by the automaker. Springs are as much to thank for a comfortable ride as they are for a driver's control over the vehicle. Not all springs are the same, though. Different types are used for multiple reasons, with the most common on vehicles today being coil springs and leaf springs. 

2006 Suzuki DRZ400 Coil Spring. Hank O'Hop

Coil Spring 

Coil springs are exactly as the name describes — a coiled spring. If you're driving a late model vehicle, there's a good chance you'll find these supporting both the front and rear, while older trucks and some cars generally feature them exclusively on the front end. Depending on the application and the suspension configuration, these can be found as an individual component or mated to the shock absorber as a coilover setup. 

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Leaf Spring 

Leaf springs setups, consist of a single (mono-leaf) or pack of semi-elliptical steel springs (multi-leaf), with the axle mounted to the center or slightly offset in most instances. Typically, you'll find leaf springs in the rear of a truck, but they've been used in a variety of different vehicle types over the years, including performance cars and motorcycles.

Different Springs for Different Suspension Setups

So, which is better? As with anything automotive, there's no universally superior solution. Only the right tool for the job. Either type of spring has its share of strengths and weaknesses, and selecting which is appropriate depends on a few factors.

There's more to consider than just the basic spring type. As alluded to the brief look at leaf springs, the spring type selected is dependent on other key components of the vehicle's suspension and driveline.

Leaf springs are typically responsible for supporting the vehicle and locating the axle assembly. While advantageous for low production costs and simplistic upkeep, it does generally limit the vehicle to a solid axle setup, which isn't known for comfort or performance.

Coil springs as seen on my 1977 TS185 project. Interestingly enough, a suspension system like this matches modern standard in a number of ways, but is viewed as dated nonetheless. Again, there's more to consider than just the spring. Hank O'Hop

Coil springs often have a much simpler role as they are simply the springs used in the vehicle, not a structurally definitive component. They are generally present in better designs such as an independent suspension, where improved articulation enhances both performance and comfort characteristics. Coil springs are also often featured in solid-axle systems, such as a 4-link, which is superior to keeping a the axle in place and eliminating issues unique to leaf springs, such as axle wrap — something high-performance applications with solid axle leaf spring setups are plagued by.

That said, these are very general overviews with room for exceptions. An example being the Corvette, which notoriously used transverse leaf springs in an independent rear suspension setup prior to the modern mid-engine C8. This is why it's important to evaluate the entire package, not just the type of spring featured.

Naturally, one has to wonder where leaf springs fit in when most suspension systems featuring coil springs are generally superior for most driving situations. Obviously, automakers continue to use them for a reason.

These leaf springs beneath my 2003 Ram 1500 better illustrate the spring's dual role of supporting the vehicle and locating the axel assembly. Hank O'Hop

Leaf spring suspension systems may have some big shortcomings in this comparison, but they pull ahead in terms of weight capacity. Coil spring suspensions are a viable option for most loads hauled by today's motorists, but leaf springs are still the better option for heavy-duty applications. This is why you'll still find them under passenger trucks, vans, and many commercial vehicles. 

Weight and space savings are another potential set of benefits not to be ignored, and Chevrolet isn't the only one to take advantage of them in performance applications of recent times. KTM showed its hand in a recent patent. This patent confirms the Austrian motorcycle company is developing a leaf spring for use in its motocross bikes. Because it's a single leaf, not a leaf pack, it's a simpler, more compact alternative to coil springs that frees up a lot of room at the rear of the bike. While little else is known about the applications it may be used for, it goes to show that there are a few reasons leaf springs still have a place in this world and they should not be written off simply due to their typical nature. Remember, it's not what is used, but how it's used that's important.

Is it Worth Making the Swap?

The wheels are turning. I already know what any of you with leaf-sprung vehicles are thinking. You're thinking about making the swap to a coil spring setup. After all, aftermarket 4-link kits are available, and would really help that truck fly through the trail or your classic hook like never before. 

The swap really isn't that simple, though. You are converting to an entirely new type of suspension system, which presents a set list of issues you may not expect. Every situation is different, but it's not uncommon to have to alter the structure of the vehicle to some degree and relocate parts due to their original positioning being heavily influenced by the original suspension system. That said, for all-out performance, it's hard to beat what coil-sprung suspension systems bring to the table. 

But in all reality, the price will determine what's going to work best for you. Most of us will have to make do with what we've got. That's not as bad as it seems, though. 

It's important to remember that leaf springs have been around for as long as cars have. That means countless builders have had many years to figure out different ways to make them work for virtually any driving situation you could imagine. While many of those modifications have been forgotten over time and buried by marketing for new and shiny suspension systems, a little bit of archaeology is all it takes to uncover them.

A good example of this is the leaf-link system I recently discovered in my old Direct Connection book, which was put to work on some serious drag cars of the era. Sure, a coil spring setup is probably better in a number of ways, but it's proof that there are ways to make anything work.

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