My fellow Autopians, welcome to the second version of Suspension Secrets and techniques, the place we dive deep into the workings of among the most iconic suspensions ever produced. This time we’re going to look carefully on the fascinatingly totally different rear suspensions accessible on the most well-liked truck in America for the previous 47 years. (in keeping with Ford): The Ford F-150. How did Ford provide such totally different designs on the identical fundamental truck platform? Didn’t they’ve to alter the body? Isn’t that ridiculously costly for an automaker to do? Let’s dive into it.
The Three Completely different Ford F-150s
Whereas Ford doesn’t get away gross sales by mannequin, I feel I’m proper in stating that almost all of F-series vans bought are F-150’s (versus F-250s, 350s, and many others), and nearly all of these are work vans — contractors’ vans, fleet gross sales, and many others.
Merely, these vans are supposed to work. They have to be sturdy, sturdy, powerful, however not essentially able to nice trip and dealing with and even off-roading past driving within the muck at a job-site. A easy suspension is all that’s wanted for these duties. Sure, it’s true that many F-150’s are bought as private day by day use autos and can by no means see dust. I’m not a contractor nor do I personal a fleet, however I’ve owned an F-150 for the previous 21 years now, and whereas I do usually use it for trucky kind duties, the fact is that it’s primarily a day by day driver. And as you would possibly anticipate, its trip suffers on account of its “work-truck” rear suspension.
However not all F-150’s are supposed to be work vans. The Raptor, for example, is supposed for off-roading, able to going by way of the desert at excessive velocity. It doesn’t must have the payload capability of a piece truck, nor does it must tow heavy trailers. As such, its suspension must be designed to maximise off-road efficiency by way of massive quantities of suspension journey and many articulation with minimal binding.
Equally, the Ford F-150 Lightning, whereas nonetheless billed as a piece truck, has very totally different calls for placed on its suspension due to its distinctive powertrain. An electrical motor with its massive battery pack want a really totally different kind of rear suspension than both a fundamental work truck or a desert truck.
Whereas the entrance suspension is identical or comparable on all three of those variations, the rear is the place the variations lie, so let’s take a deep dive into every and see what makes them tick and why they have to be totally different.
Earlier than we do this, click on the video above for half II of our Suspension Secrets and techniques sequence — this episode goes deep into the three main Ford F-150 suspensions, and it’s gold.
Let’s Look At The Base Suspension
For the reason that starting of transportation units, the most typical kind of suspension has been the leaf spring. This goes again to the early days of wagons and was carried by way of into the age of vehicles. The evolution of leaf springs has gone from totally elliptic:
Picture by way of: Memorabilia: Leaf Springs – Franschhoek Motor Museum (fmm.co.za)
….to three/4 elliptic:
Picture by way of: Rios (Wikimedia commons)
There have even been quarter elliptic variations alongside the best way (the Austin-Healey Bug-Eye (Frog-Eye) Sprite and MG Midget come to thoughts):
Picture By way of: 1959 Austin-Healey Sprite for Sale | ClassicCars.com | CC-1800818
However the most typical kind utilized in vehicles and vans over the previous 100+ years is the semi-elliptic model in a suspension design generally known as the Hotchkiss suspension:
All F-series vans, going again to the very first one, the F-1 launched in 1948, have used this fundamental suspension design, and that continues at this time. It consists of a strong axle held by two leaf springs. The springs are connected to the body at their entrance finish with a rubber bushing and a welded-on bracket, and on the again finish by way of a shackle that permits the spring to alter size because it flexes Right here you may see how the shackle within the rear has to articulate to permit the spring to bow and straighten because it flexes up and down:
Right here I’m pointing on the base F-150’s entrance leaf spring mount on the passenger’s aspect:
And right here’s the place the leaf spring mounts to the shackle, which mounts to the body (observe: the shackle is the wrong way up in comparison with the graphic above, but it surely works the identical means — it swings because the spring “straightens’ and turns into longer within the fore-aft dimension):
For a few years, this was the dominant kind of suspension in all autos, vehicles and vans. However as consolation, trip, and dealing with turned extra vital in vehicles, the deficiencies of the design led to its substitute first by coil-sprung multilink reside axle designs and eventually by unbiased suspensions. Hotchkiss suspensions are easy and low-cost, however by asking the springs to primarily act as all of the suspension linkages (i.e. not simply to be springs, but additionally be charged with holding the strong axle fore-aft, side-to-side, and stopping it from rotating), they’re at all times going to be a compromise.
The primary issues with leaf spring suspensions are wind-up below braking and acceleration, and twist throughout roll. Wind-up, or axle “wrap,” is brought on when the torque of acceleration or braking tries to deform the spring into an S-shape. Right here’s a glance from the aspect of the truck:
If the engine has quite a lot of energy, the tires can lose traction. When that occurs, the spring snaps again to straight. When the tire regains traction, the spring twists again into an S-shape till the tire loses traction once more and the cycle repeats itself. In dangerous instances, this could occur a number of occasions per second and trigger a violent shaking within the automobile. Most leaf spring suspensions have staggered shocks to scale back this impact but it surely by no means totally goes away.
The opposite drawback is that when the automobile rolls, like in a flip, or when one wheel goes over a bump, the spring must not solely transfer up or down but additionally to twist. The following animation doesn’t do job of displaying it however you may think about how the center of the spring the place it’s connected to the axle must rotate with the axle, whereas the ends the place they’re connected to the body wish to stick with the body. The result’s a twist alongside the size of the spring and within the bushings — twist that the spring and bushing will strive to withstand.
This implies the spring stiffness in vertical movement is simply the vertical stiffness, whereas in roll it’s a mixture of the vertical stiffness and the twisting stiffness, making it a lot tougher to seek out the best steadiness between trip, dealing with, and luxury. This additional stiffness in roll additionally means the suspension has extra resistance to articulating over rocks and bumps — nice for a piece truck, not so good for a truck that has to maneuver rapidly over tough terrain. That brings us to the Raptor.
F-150 Raptor Suspension
When Ford launched the Raptor again in 2010, it tried to make a manufacturing off-road racing trophy truck. For essentially the most half, it labored, however whereas the picture was definitely there, you can argue the efficiency, whereas good, wasn’t fairly as much as the duty. The truck received new entrance suspension bits to push the wheels out, and a wider rear axle, however the fundamental structure was carry-over from the bottom truck and suffered from the identical leaf spring associated points we mentioned earlier than. That is completely regular for what was then an unproven idea, since structure adjustments are costly and you should hold prices down at first.
However as gross sales improved and the truck gained a strong following, the constraints of the bottom platform turned a legal responsibility, not an asset. So, with the introduction of the third era in 2021, the Raptor ditched the leaf spring rear suspension in favor of a five-link consisting of 4 trailing hyperlinks, a panhard rod (or monitor rod), and coil springs (you may get an in depth have a look at the {hardware} by studying our assessment of the 700 horsepower Raptor R). Dropping the leaf springs meant not having to take care of the twisting of the spring in roll and the related limitations in articulation. A five-link can articulate un-impeded till the springs and dampers attain their journey limits. There may be nonetheless a little bit of twisting occurring within the hyperlinks themselves, however that is a lot simpler to take care of than in a leaf spring. (Right here’s our full article on the benefits of this coil-sprung setup of a leaf spring setup)
After all, altering from leaf springs and their related brackets to coil springs and a number of hyperlinks meant some vital adjustments have been wanted to the body. I can’t say for sure, however to my eye, the principle fore/aft rails of the body weren’t modified, however each bracket welded to the body associated to the rear suspension has been modified. The brackets that held the entrance of the leaf springs are changed with a a lot bigger brackets the place the higher and decrease fore/aft hyperlinks connect:
The brackets the place the rear leaf spring shackles connect on the bottom truck are fully gone however now now we have massive brackets that assist the tops of the coil springs and join the body finish of the panhard rod:
Equally, there are actually new brackets on the axle itself to attach the fore/aft suspension hyperlinks and the panhard rod, in addition to the underside ends of the coil springs:
Lastly, the dampers are actually each positioned on the entrance aspect of the axle as a result of the fore/aft hyperlinks care for the twisting throughout braking and acceleration. Staggered shocks usually are not wanted with this design.
That’s a LOT of change to the body, and quite a lot of expense to spend on new, distinctive instruments to construct what is basically a specialty mannequin. Having mentioned that, as we famous earlier than, F-150s promote in very massive numbers. Meaning quite a lot of components have to be made to assist that sort of manufacturing quantity. It’s unlikely {that a} single set of instruments might do this for all F-150s, anyway, given what number of are bought. Manufacturing instruments have a restrict on how rapidly they will produce components, and in case your manufacturing necessities are greater than that, you want a number of units of instruments. If Raptor manufacturing numbers are anticipated to be excessive sufficient, they could push the manufacturing capability of the prevailing instruments over the sting, requiring one other set of instruments, anyway.
When an organization finds itself in that state of affairs, it actually isn’t that rather more costly to make these new instruments distinctive. It then begins to make sense to make a brand new design that improves the product and provides you a aggressive edge. I’ve no insider data to know if this was the case when Ford determined to make the Raptor rear suspension distinctive, however I do know that tooling capability considerations are a part of these selections.
F-150 Lightning
Being an all-electric truck, the F-150 Lightning (learn our ridiculously in-depth technical assessment right here) faces a really totally different set of challenges than the Raptor. Within the base gasoline truck, the engine sits within the entrance, and a driveshaft runs from the again of the transmission to the rear axle. For the reason that axle is a reside setup, the driveshaft wants to have the ability to transfer up and down with the suspension. Sadly, the driveshaft and the area it wants for this movement sits proper in the midst of the truck the place we have to package deal the big battery an EV requires. We have to get the driveshaft out of there fully so we are able to use the area for batteries, which suggests we are able to’t merely change the ICE motor with an electrical motor and name it good. We have to transfer the electrical motor to the rear, near the rear wheels, so all of that stuff is out of the best way of the battery.
We might simply bolt the motor on to the strong axle, which is what some have proposed as a solution to cheaply convert present vans to EV energy. However this implies the motor is shifting up and down together with the axle over highway bumps. That’s a LOT of mass shifting round. Not solely that, however the excessive voltage/excessive present wires that join the motor to the battery would want to flex up and down with the motor/axle as nicely. That’s a recipe for early failure of the wires, and contemplating the facility they’re carrying, not situation on the whole.
We’re left with bolting the motor on to the body, and when you’ve gotten up to now, you recognize you will have a set of halfshafts to attach the motor to the wheels. An unbiased suspension then turns into the one structure that basically is smart. And that’s precisely what Ford did, and what each EV truck producer thus far has accomplished and is anticipated to do (each the Ram and Silverado EV’s are anticipated to have unbiased rear suspensions).
Placing an unbiased rear suspension within the F150 requires a complete new stage of change past something accomplished for the Raptor. Ford selected a semi-trailing arm structure for the Lightning that consists of a single massive aluminum forged arm per aspect, related to the body with a pair of bushings. The springs and dampers have been changed by coil-over damper modules related between the rear fringe of the trailing arms and the body.
After all, these new components require new brackets on the body to connect to. New cross members have been added to connect each the trailing arms in addition to the motor:
New brackets have been made to connect the tops of the coil spring modules:
However there may be one change that isn’t apparent, however is not any much less vital. The peak of the rear body rail within the Lightning has been lowered, and is now instantly consistent with the rear bumper. That is no accident, and the explanation that is doable is that there isn’t an axle housing shifting up and down beneath the body. This graphic reveals how the motion of the Raptor and base truck’s strong axle means the body rail needs to be pretty excessive to permit it to achieve full journey (ignore the spring interfering with the body, that’s simply dangerous modeling on my half):
In an unbiased suspension, there isn’t any axle tube shifting up and down so the body rail will be positioned a lot decrease. Each Ford and Chevrolet made use of this reality after they transformed their massive SUV’s from reside axles to unbiased – Ford within the case of the 2003 Expedition and Chevrolet with the newest Tahoe. In each instances, the decrease rear body peak meant vastly improved third row seating package deal with a a lot decrease flooring.
With the Lightning, the decrease body rail has not translated into higher room since Ford nonetheless makes use of a cargo field widespread with the remainder of the F-series lineup, however sooner or later, it might result in a deeper field. You may see the distinction right here between the bottom body rail:
And the Lightning body rail:
Right here’s a clip displaying the distinction:
However why trouble doing this? Why not simply hold the identical rails and weld totally different brackets to them? The rationale, I feel, is that having the body rail inline with the bumper makes for a way more environment friendly crash construction within the occasion of a rear finish collision. Within the case of the bottom truck, the forces coming from the bumper throughout an influence should jog from the bumper, as much as the body rail after which down once more as soon as they get previous the suspension. When forces should “jog” a technique or one other, they have a tendency to trigger the rails to bend and fold, moderately than crush, and bending is a really dangerous solution to take up crash forces. For those who can direct the crash forces in a straight line, the rails will be designed to crush properly and effectively take up the crash forces.
One other solution to take care of the issue is to make the “jog” space very stiff and powerful so it doesn’t fold. You may see how Ford used varied brackets within the base body so as to add quite a lot of metallic to the rail and stiffen that space. The Lightning rail is way easier with out all these reinforcements.
One other clue will be seen within the Lightning rail. Discover the 2 sq. cut-outs on the sides of the rail and the 2 spherical holes close to them:
There are literally two extra on the opposite aspect of the rail and these most probably type what are generally known as “crush initiators”. What they do is weaken that space of the body and trigger it to buckle there first. Doing that causes the remainder of the rail to crush in an accordion style. Here’s what that appears like:
Picture by way of: Aluminum Extrusions Show Superior in Bumper Techniques – Gentle Metallic Age Journal
The dimples on the prime of the left undeformed rail play the position of the sq. cutouts within the Lightning rail and begin the accordion deformation which then continues down the remainder of the rail. Discover that the bottom F-150 rail doesn’t have any cut-outs or different initiators like this. That implies to me that the rail is just not meant to deform however to remain as inflexible as doable. Within the case of the lightning, this preliminary upward jog is eradicated and the rail will be designed to crush and effectively take up crash vitality. A significantly better design throughout.
The F-150 Has Three Very Completely different Suspensions All In One Fundamental Truck Structure
Three very totally different rear suspension designs — a strong axle held by leaf springs that do every thing, a strong axle held by 5 hyperlinks and sprung by coil springs, and a totally unbiased suspension — for 3 totally different functions. Horses for programs, as they are saying. Ford is lucky to have the gross sales volumes within the F-series vans to have the ability to afford so many various architectures, customers are lucky to get the very best setup for the F-150 variant they selected, and we right here at The Autopian have been lucky to have some cool stuff to take a look at and dig into.
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