Pickup Trucks 101: How Suspension Systems Work

2017 Ford F-250 Towing Camping Trailer II

By Matthew Barnes

The suspension system is one of the most important components of any vehicle. The system must be engineered to handle expected and unexpected conditions when driving. When considering suspension systems, be prepared to make compromises regarding ride quality, load capacity, price, space and durability.

There are a variety of suspension types on the market today and they all function differently, each with their own strengths and weaknesses. Here is our guide to understanding them.

Independent Versus Solid Suspensions

It's important to understand the differences between independent suspensions and solid (also called live) axle suspensions.

On independent suspensions, the wheels on an axle act independently from one another. Nearly all vehicles today, apart from some heavy-duty full-size pickups, have independent front suspensions. If one side hits a bump or a dip, it acts independently of the other side to compensate for the disturbance. This helps to smooth out the ride and keep it from rocking from side to side as it does with a solid axle suspension.

Independent suspensions can free up space for other components in certain applications, such as the rear cargo area of SUVs. Independent suspensions have higher ground clearance, which makes them good for off-roading, and a smooth ride during uneven desert running. For example, the military M1152 HMMWV has 18 inches of ground clearance underneath the center differential. The downside is that in most cases, independent suspensions offer less wheel travel than solid axles do.

2017 GMC Sierra 3500 Front Torsion Bar  Independent 1 II

When pickup enthusiasts hear the word axle, often the first thing that comes to mind is solid axle. A solid axle connects the wheels with a bar or a tube. If it is a driven axle (meaning it transfers power from the engine through the shafts), the differential will be placed somewhere in the middle of the axle. When a wheel on a solid axle hits a bump or a dip, it directly affects the wheel on the other side of the axle. This can make the vehicle rock from side to side and create a rougher ride. Solid axle suspensions are usually less complex than independent axles; they often are thought of as more durable and easier to work on. That said, many military vehicles — which see some of the worst driving conditions in the world — have independent suspensions.

When driving off-road, solid axles create more articulation. The increased articulation comes from the pivot point that is created when one wheel is on higher ground that the other. The pivot point is where the spring suspension connects to the axle; this motion can apply more load to the lower wheel, increasing its traction. Solid axles have lower ground clearance, but they are still preferred for rock crawlers for their extra articulation and strength.

Jeep with Solid Front Axle II

Coil Springs Versus Leaf Springs

Coil springs can be used in both independent and solid axle suspension systems. They are the most common spring used for suspension on vehicles today, and they are useful in a wide variety of applications. They can have a variable spring rate, meaning that the more the spring compresses, the stiffer it becomes. This helps create a smooth ride while allowing a pickup to carry a heavy load.

Coil springs weigh less than the longer leaf springs and can provide lots of articulation. When used in solid axle suspensions, coil spring suspensions don't have nearly as much wheel hop as leaf springs do. This is because control arms are used to keep the axle in place. Coil springs typically aren't as durable as leaf springs and can sag over time. Coil springs also are used in coil-over suspension systems, where the shock is placed inside the coil spring to create a compact suspension system. Coil-overs can be found in SUVs such as the Ford Expedition and Toyota Sequoia, and pickups such as the Titan and Titan XD.

2017 Titan XD Front Coilover II

Leaf springs are the oldest type of automotive springs. They are used on solid axle suspensions and are currently only being made for the rear axles of pickups, vans and commercial vehicles. Leaf springs hold the axle in place as well as suspend the weight of the vehicle, which means control arms are not necessary. Like coil springs, leaf springs have a variable spring rate and can even have extra springs, called overload springs, that only engage once the vehicle has been loaded to a certain weight. More leaves can be added for extra stiffness and load-carrying capacity. If one leaf breaks, there likely will be enough support left in the other leaves to get the vehicle to a repair shop without damaging it. The disadvantages of leaf spring suspensions are that they can be noisy, they ride roughly and are prone to wheel hop.

2017 Ford F-250 Rear Leaf Spring  Solid Axle II

Torsion Bars

Torsion bars, also known as torsion springs, aren't as common as other suspension systems; however, GM still uses them on its pickups. Torsion bars are only used in independent suspension systems. Torsion bars are long, round bars that act as a spring because of their twisting strength. One side of the bar is mounted solidly onto the frame, while the other end is mounted into the lower control arm of the front suspension. Torsion bars resist wheel movement by twisting when a wheel moves up or down. They are the simplest automotive spring. Like leaf springs, they are durable and will likely outlast the vehicle. The drawbacks are that they don't have a lot of wheel articulation when compared with coil and leaf springs, and they don't have a variable spring rate.

2017 GMC Sierra 3500 Front Torsion Bars  Independent II

Air Springs/Air Bags

Air suspensions are the most complex suspension systems offered. They include valves, an air compressor, air lines, height sensors, control modules, air reservoirs and the air springs themselves. Air springs are used on both independent and solid axle systems, and air bags are most often used with solid axles in the rear suspension to level a loaded vehicle.

Air suspensions are the most versatile suspension systems. Vehicle ride height can be adjusted on the fly. This means when the vehicle is in a rough off-road spot, the suspension can lift it to give it more ground clearance. When cruising down the highway, the suspension can lower the vehicle to reduce drag and increase fuel economy.

Many air suspension systems are included with optional packages that have shocks with adjustable damping as well. Between the adjustable air suspension and adjustable shocks, the user can set the vehicle to ride like a 1980s Lincoln Town Car or like a one-ton diesel truck, depending on his or her preference. Other benefits include leveling the vehicle when it is loaded, and lowering the vehicle for exit/entry and cargo loading. However, these systems make it easy to overload a vehicle, they are expensive to repair and there is a higher likelihood of a suspension component malfunctioning.

Ram Rebel Front Air Spring II

Summing Things Up

Automakers design vehicles to meet the needs of the most people possible so that they can sell more vehicles. This means that most SUVs will have independent front and rear suspensions for a smoother ride on the road. Heavy-duty trucks will at least have a rear solid axle; Ford and Ram HDs have a solid front axle as well. Most HD trucks have leaf springs in the rear. Luxury vehicles and some factory off-roaders such as the Jeep Grand Cherokee, Land Rover Discovery and the Ram 1500 Rebel have air suspension with adjustable-ride height.

When selecting a new vehicle, seriously consider how it will be used and then determine which suspension system will work best for those applications. That could narrow your choices considerably. The suspension system most likely won't be the deciding factor on a new- or used-vehicle purchase, but it should play an important part in that decision.

Cars.com photos by Matthew Barnes

 

Ram 3500 Rear Air Bag II

 

Comments

How can you talk about modern suspensions without at least a passing reference to struts?

@papajim - This article had nothing to do with suspension systems. It was just an article explaining differences in spring types, which struts use coil springs. It was simply an overview, not a technical article

This article had nothing to do with suspension systems.
Posted by: Toycrusher

@toycrusher

Please see title: How SUSPENSION SYSTEMS work

Try reading for comprehension. It can be very satisfying.

Anecdotally, I have seen a lot (possibly a majority) of big rigs with air suspension all around. Considering the types of miles and conditions those vehicles see, would you say that the trucking industry has found a way to deal with the notion that air suspension is less reliable? Would it be because big rigs are inspected more frequently/thoroughly than non-commercial vehicles? Or could the parts be engineered better?

Would it be because big rigs are inspected more frequently/thoroughly than non-commercial vehicles? Or could the parts be engineered better?
Posted by: djjr50

@djjr50

Good question. It could be related to the fact that a halfton Big 3 sort of truck sells for a small fraction of what you'd pay to buy a modern big rig.

Something not addressed in the story is the sort of suspensions you see on firetrucks and large emergency vehicles. Again, a firetruck these days is a custom built proposition that can list for over a half million dollars. Air suspension involves a bunch of moving parts.

Here is papajim teaching us about struts and struttin.

https://www.reddit.com/r/PublicFreakout/comments/258d4f/can_anyone_explain_why_this_man_is_upset/#bottom-comments

papajim Struttin'

https://youtu.be/nft9Y51IOfc

An acquaintance of mine's Land Rover air suspension just went out. One of the pumps failed. Something like that. The mechanic said it is better to replace all four pumps since he's into the system now. Anyway, needless to say, it's an expensive job. My acquaintance didn't youtube to try and repair himself, so I figure if he's not willing to attempt to do one of the pumps himself, with the learnings from that surely transferable to when/if the other three go out, then don't bitch about the price. Auto-lowering and raising seems to be great for loading these full-sizers when compared to the compact trucks of the past, but yup another thing to have to repair.

@DJJR50- Class 8 line haul trucks see tons of miles, but often the time between major service work isn't that long. We had some Schneider team driven trucks come back with 3/4 million miles in only a few years. Air-bag suspensions are the only good way have a vehicle work with such huge load variations. It also lets you hook and unhook trailers easier. Well installed or factory original airbags can last a really long time- its often small alignment, pinching or friction issues that shorten the life of aftermarket bags.

The Tundra has the beefiest IFS on any half-ton truck, no wonder they are so popular for offroad built trucks. 10" of wheel travel from the factory IFS on standard run of the mill Tundra is impressive.

The Raptor has 13" of front wheel travel from the midtravel IFS

Matthew - - -

I realize you were trying to do a quick brush-stroke, once-over summary of this topic (not an easy task!), but there are some "independent suspension" biases and omissions here:

M: "Nearly all vehicles today, apart from some heavy-duty full-size pickups, have independent front suspensions."

You forgot to mention Jeep Wranglers, which are selling like hot cakes.

M: "For example, the military M1152 HMMWV has 18 inches of ground clearance underneath the center differential."

The "Humvee" has unusually high ground clearance because of a special military style, 3-part, disassembly-capable, independent suspension; AND the use of PORTAL axles. It is not an appropriate example: you would never see that on a commercial vehicle made in this country.

M: "The disadvantages of leaf spring suspensions are that they can be noisy, they ride roughly and are prone to wheel hop."

1) I have NEVER had noise issues with any leaf springs on any truck or other vehicle, and have been driving for 54 years. I can say that some VERY old pickups, with poorly made and assembled springs-packs, might have suffered from a "rattle", but no American vehicle with leaf springs in the last 30-40 years would suffer from that.

2) Leaf springs do NOT invariably ride any rougher than any other type of spring. It all depends on the how they are made; the spring rates chosen; how many leaves are used; whether a feather springs is selected for the "upper"; the length of the spring packs; the fastening system; use of inter-leave friction/slider pads; etc. Some leaf-spring systems have leaves mounted parallel to each other without any contact between leaves. You simply can't generalize this.
(I should say that good leaf-springs require good length, such as 60 to 72 inches, not easily done in smaller vehicles, which is why coils became common in sedans.)

3) Wheel hop? For usual driving, nonsense. "Wheel hop" only occurs under extreme power delivery or extreme braking, and may occur for ANY suspension system. For an extreme example, take a look at this video (Spanish) of the Jeep Renegade, with independent suspension, under emergency braking:
https://www.youtube.com/watch?v=dCEthdH7iYw

The durability aspect of leaf springs is not addressed enough in this article. We are talking pickup trucks, after all: right?

It has only been since WWII that metallurgy has advanced enough for coil springs to be practical for standard use. But I have never NOT had coil springs sag or break, regardless of vehicle (especially when stressed in sub-zero temperatures); and I have ever had any issues with ANY leaf springs whatsoever.

REASON: Leaf springs put the interior metal structure into only ONE mode of deformation: flex (or bend).
Coil springs, on the other hand, stress the metal "wire" (as it's called) into THREE modes: torsion; compression; and (surprisingly) elongation, --- all simultaneously. This is literally torture for the metal matrix: it's trying to tear itself apart.

I could go on, but I'll stop for now (^_^)...

===================

Thanks @papajim and @mrknowitall. That is what I thought...the service intervals and attention to the air systems make them reliable.

I wonder what transverse leaf springs would hold up in a pickup application? I also wonder how much less (if at all), you'd be able to tow and haul in a half-ton application if the rear suspension was ALSO independent axles?

Here is papajim teaching us about struts and struttin.

https://youtu.be/nft9Y51IOfc

Posted by: Nitro B. | Jun 22, 2017 11:12:38 AM

Is this really papajim? It sounds like him.

Not my comment but it is hilarious. I actually thought is was papa.

Actually, it is not just because a vehicle has leaf springs it gets axle hop.

For years Chrysler leaf springs were known for not tapping wheel hop/axle wrap due to the axle being placed more forward on the leaf, plus the leaf construction, as opposed to many GM cars with leafs. Camaros and Novas always had their share of issues.

When I races dirt track in Hawaii, the Camaros and Nova racers would install "traction bars" to control it.

Nowadays, people running leads on race cars often get the Chrysler design if they can get away with it.

It is not limited to leaf springs, either. I had a,1976 Chevy Monte Carlo, and it was a wheel hopper!


TORSION BARS: they don't always mount to the lower control arm.

I have seen Toyota 24 (or so) passenger busses where the TORSION bar goes to the UPPER control arm.

Also, some Torsion bars do not mount to the pivot point on the lower arm , they often mount an inch and a half or 2 away from the pivot point, ie, my 2006 Chevy 4x4 truck.

This makes the t bar not just twist, but bend as well.

Not HAVING, I said, not "Not tapping"

@ Angelo; I agree & although air-suspension sounds like the best ultimate choice to have on a truck/4WD vehicle, I've had experience of issues with family/friend's Range Rovers (a 93' Range Rover & a '13 Sport model); to many issues with leaks & costly repairs. Worst still, when one side goes out, the whole vehicle is lopsided & not safe to drive & like you said; Land Rover mechanics will always insist to change all key parts while at it.

This is another reason why I would never buy a RAM truck with air suspension, they are always nice the first couple of years even when you know it's just trouble waiting to happen especially with their well known reputation of reliability.

Posted by: Angelo Pietroforte | Jun 22, 2017 11:39:26 AM

Torsion bars are not mounted to the lower a-arms!

Toyota had them mounted to the upper a-arm, giving a taller stance and providing full protection from the frame unlike GM!

Solid axles are DONE!

If the military does not use them, why should you?

Lower rear shock mounts, why does the big three still place them so low and vulnerable?

With my 1986 Toyota baja truck, we ran a larger diameter torsion bar (factory mounted to the upper a-arm, thus better protection and ground clearance), limiting straps, and placed the dual shock system lower mounts on top of the upper a-arm and into the engine bay with a custom over engine hoop.

This also acted with a rubber stop to hold the engine down in case of motor mounts breaking during races.

Rear suspension was a typical 11-pack National Spring mounted above the axle as the factory did, unlike big three trucks, dual shock system that never went below the axle line, again unlike big three trucks, limiting straps, and a bar welded top center of the axle to the back of the diff housing to prevent axle wrap and flexing of the axle under load.

My 2005 Tacoma X-runner had larger diameter sway bars front and rear, negative front camber set at 2 degrees or more, Renton coil springs 20% stiffer and dropped the front 2 inches, rest was factory.

Rear had custom 3 inch drop block, Calvert traction bars, and a custom Watt's link system installed, rest was stock.

My 2010 Tacoma has OME 200 lbs. front coils with nitrogen charged shocks, 3 inches of clearance, Camburg upper a-arms that retain factory ball joints.

Rear has a custom 9-pack Deaver springs rated 700 lbs. over stock, u-bolt flip system for better ground clearance, custom rear shock hoop system where both Fox 2.0's with 14" stroke are mounted before the axle, angling forward and custom welded tubes on the axle to prevent axle wrap and flexing under load much like the baja truck.

My 2016 Tacoma is stock from factory with 265/75's on 16x7 rims. Yes, I prefer 16" rims for more rubber and airing down capabilities!

@djjr50- transverse leaves are an interesting arrangement- Depending on mounting, the spring maintains more even pressure on both sides of the axle. That's great for going straight, tricky for turning corners.
IRS on a half ton... hard to say, but the Ridgeline and 2nd gen Explorer sport track had comparable tow ratings to the rest of the segment. The Ford Expedition, Toyota Sequoia, and Nissan Armada all use IRS and they tow every bit as much as a Tahoe or Suburban. I doubt you'll see mainstream IRS in full-size trucks any time soon, but coil springs will make more inroads.

Solid axles are DONE!

If the military does not use them, why should you?


Posted by: oxi | Jun 22, 2017 11:41:01 PM

Why do you think G.M. H.D's have no where near Ram and Fords tow ratings. BINGO front IFS.

oxi - - -

O: "Solid axles are DONE!"

Hardly. Of commonly available drive systems for serious off-road use (i.e., Jeep Wrangler), solid axles provide:
1) Lowest cost
2) Greatest toughness and durability
3) Easiest modification ability
4) Superior traction in undulating terrain
5) Largest articulation (Ramp Travel Index)

O: "If the military does not use them, why should you?"

Already explained above (Jun 22, 2017 12:09:39 PM), amounting to the fact that the Military has tons of money to throw at their heavy, expensive, fuel-inefficient, three-piece axle, --- with ORBITAL drive at the wheels. Who is going to pay ~$50K for an over-engineered, complex, suspension system when the new vehicle itself (outside of that system) cost $40K?

=======================

Solid axle- superior for hd towing/hauling, I'll never have anything else in a hd truck again.
Ifs- superior in off-road/uneven terrain but a PITA for hd towing/hualing

Leaf springs- usually have higher payload and simplicity. They do make noise tho, but only as they settle under heavy load
Coil springs- not as high payload without complex geometry involved but softer ride and can be noisy also but not as often
Torsion bars- not good at all for hd use, longest lasting tho. I'll never have torsion bar suspension again tho, I was constantly changing rubber bushings under the floor board when they would start to make noise

Gasser V8 - - -

Good summary.

G: "Coil springs- not as high payload without complex geometry involved but softer ride and can be noisy also but not as often"

Just got a Ram 2500 with coils all around. Reasonably smooth ride and no suspension noise yet. But it's new. Let's see what happens as it ages. Coils do sag with time. Yes, the rear is a complex mess of control arms that a leaf-spring setup would not have.

BTW: I test drove a Ram 3500 (Leafs) against a Ram 2500 (Coils) with a sound meter recording while going over RR tacks and rough pavement. RESULT: The peak of the acoustical sine wave was about the same going over bumps (total energy of impact was therefore about the same), but the onset angle at the base of the wave was a little shallower with rear coils, which we interpret as a slightly smoother ride. The difference was not slam-dunk huge, however. If the leaf-pack in that 3500 were made a bit differently, I suspect the ride quality would be indistinguishable from that with coils.

A better test would have occurred if an accelerometer were placed on the passenger's seat, and the run over RR tracks and potholes repeated. I did not have one of those, but I understand that a cell-phone app is available to measure that phenomenon.

===================

oxi - - -

O: "Lower rear shock mounts, why does the big three still place them so low and vulnerable?"

Yeah. I've wondered that myself: the lower rear shock-mounts actually hang BELOW the rear axle!

All I can suggest is that they do this to allow the longest-travel shock-absorbers possible, for good articulation and shock-travel range, or the shocks might just be stubby little things...
... or, if they kept the regular length shocks, perhaps so that the body of the vehicle would not be suspended up high from mounting on TOP of the axle, --- which would raise its COG and make entry/exit for occupants more difficult.

========================

Here is papajim teaching us about struts and struttin.

Lower rear shock mounts, why does the big three still place them so low and vulnerable?


Posted by: oxi | Jun 22, 2017 11:41:50 PM

Why does Toyota make their truck frames out of recycled junk metal? Aren't they tired of getting sued for billions of dollars because their frames are compete junk?

And why does Toyota let the exhaust and transfer cause hang below the bottom of the frame where it's easily damaged? I mean it hangs down right in the breakover are of the truck where you are almost guaranteed to hit something as you rock crawl. What idiots hahaha!

Wow this was so informative on how different suspension systems work. I never thought of the difference between coil springs versus leaf springs until this article. I have been looking at a new way to fix my suspensions but I wanted to know how they worked and the difference between the systems. This was really helpful, thank you.

Wow this was so informative on how different suspension systems work. I never thought of the difference between coil springs versus leaf springs until this article. I have been looking at a new way to fix my suspensions but I wanted to know how they worked and the difference between the systems. This was really helpful, thank you.



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