2010 Ford F-150 SVT Raptor: Suspension Walkaround
Ford's new F-150 SVT Raptor made an appearance in my driveway recently, and it created a bit of a stir. My tweenage daughters wouldn't ride in it. My wife didn't want any of her friends to catch her in the thing. They complained of the "kindergarten mess" graphics flanking the sides of it (an option, I told them) and compared it to a real-life sandbox toy (that part's right.)
On the other hand, the Metal Mulisha dude with the flat-billed hat down the street thought it was uber-cool. So do I. Who cares if it broke my floor jack? (To be fair, my aging floor jack popped a seal on the previous walkaround. The Raptor's burliness merely finished it off.)
Anyway, let's get to it...
Starting in the rear, we can see that the Raptor is suspended by a live rear axle, a leaf spring package and some radical-looking shock absorbers -- more on those in a minute.
In this picture the jackstand is hidden behind the brake rotor, where it is supporting the axle directly. The suspension is therefore loaded as if the truck were sitting normally on its tires, which means you can't see the impressive 12.1" of rear suspension travel, the majority of which is "droop" travel you'd only see by jacking the truck by its frame -- or by jumping it.
These leaf springs look fairly soft, with only two main leafs. The third "helper" leaf (black) is short and insubstantial. It all adds up to a more-linear rear suspension that's good at gliding over whoops and ruts in the dirt, but less-than-ideal for high payloads and large trailer tongue weights.
The listed payload for the Raptor is 1,020 lbs, but that's only if the actual truck sticks close to Ford's claimed 5,863-pound curb weight. This Raptor weighed 5,957 pounds on our scales. When we subtract that from the Raptor's 6,950-pound GVWR, we're left with an actual as-equipped payload of 993 pounds for this particular truck.
But this 993 pounds must be further-reduced by the weight of the driver, passengers and any junk in the cab. Yep, you and your buddies are payload. With two 200-pounders aboard, for example, only 593 pounds remain for cargo in the bed (such as a pair of dirtbikes) or for trailer tongue weight (just barely adequate for a 6,000 lb trailer). That's an "or" folks because trailer tongue weight is considered payload. Don't expect to tow much of anything with stuff in the bed, or vice-versa.
But a softer spring package such as this is necessary to allow the long-stroke off-road travel that the Raptor delivers. Besides, the Raptor fulfills the role of dirtbike on its own.
Most modern leaf springs (a true contradiction in terms, that) have thin spacers like these between the leaves to produce a gap that reduces sliding friction between adjacent leaves as they flex.
Raptors sit 2.2 inches higher than a standard F-150 4x4, thanks in part to this 2 5/8-inch lift block between the axle and leaf spring. The lift block incorporates the contact point (white) for the urethane bump stop.
This entire rear axle housing is wider than that found in a standard F-150 4x4, in order to boost the rear track width from 67 to 73.6 inches, a 6.6-inch gain.
I've circled the tag to point out that the rear differential requires synthetic lube.
You're looking at a "Berlin eye" leaf spring end, a type characterized by a little extra wrap that brings the leaf up to the centerline of the eye. Another common leaf spring type unwraps straight off the bottom using what's called a "turned-up eye". The Berlin eye is by no means unique to the Raptor, but it is worth pointing out.
When used at the front end of the spring, like we see here, the extra wrap of the Berlin eye reduces the tendency for the axle to migrate back as the spring compresses and the eye unwinds. (After all, a leaf spring is more than a spring -- it's also a trailing arm that locates the axle.) Rearward axle migration on one side amounts to toe-out, and that can mean roll-oversteer at the loaded outer tire in corners and twitchy-ness when the rear axle strikes a large bump on one side. The Berlin eye helps to reduce these undesireable traits.
You don't need to use a Berlin eye here because the rear doesn't locate the axle in the fore-aft direction. There may be a packaging or manufacturing reason why they did it anyway, or perhaps the #1 leaf is reversible and common to the left- and right-hand sides. That's not usually the case, however.
Furthermore, the spring connects at the top of the shackle, which improves underbody clearance and packaging. The springs have to be located outboard the frame rails, as opposed to under them, to make this work. It also means that the kind of longer J.C. Whitney shackles your dad used to jack-up the back of his Dodge Duster in high school would lower this truck, not raise it.
The crowning jewel of the Raptor's rear suspension is its Fox Racing shock absorbers, a pair of inverted dampers with a remote reservoir and internal fluid bypass. Let's take them one at a time.
An inverted shock is one where the shock body and the valving & oil it contains are hung off the frame of the truck, leaving the slender piston rod -- hidden here behind a black plastic rock guard -- to be the moving part that's bolted to the axle. You get less unsprung weight this way and the stationary shock body makes it easy to employ a remote reservoir.
In a monotube application a dividing piston isolates the oil and nitrogen gas in separate chambers within the main shock body, but the "dead zone" created by this gas chamber eats into the available stroke of the shock for a given shock body length. I've been told these are twin-tube shocks, so the internal architecture may be a little different.
Either way, the remote reservoir provides extra oil volume to help the shock run cooler. And in the typical monotube application, a remote reservoir allows the dividing piston and gas chamber to be reloacted to the remote unit, leaving the entire length of the shock body available for suspension travel. High-pressure gas would be on the left side of my crudely-represented dividing piston and oil is on the right where it can flow in and out of the main shock body through a passage hidden within the blue fitting.
Most internal bypass shocks have grooves cut into the inner diameter of the main shock body, where the piston and valve rides up and down. Damping force comes from the resistance created when you try to cram oil through tiny passages in the valve, and these bypass grooves allow some of that oil to detour around the valve, thereby reducing the damping force that's generated.
Roughly speaking, an off-road truck wants less damping force in the normal at-rest position to help produce a smoother ride on basic cracked pavement and simple washboard dirt roads, so the grooves are concentrated in the middle third (more or less) of the shock's travel. But you need a lot more damping force when you land a jump, crash into a pothole or otherwise slam the suspension toward the bump stops, so the grooves disappear as you get closer to the ends to force all of the fluid through the valve as the suspension strokes past the central on-road region. Ford says the forces generated near the ends are four times as large.
These are "triple bypass" shocks, which probably means there are grooves of three different lengths inside to progressively build the force as you get closer to the end of the travel. Neat stuff.
Fox may have accomplished all of this via another mechanism, but the principle is the same. Maybe if I ask nice they'll send me one so I can cut it open for another post on another day.
Rear braking duties are the job of single-piston (yellow) sliding calipers. A remarkably open design makes it easy to see the brake pads (white) and the sliding surface of the caliper frame on which they move.
A healthy-sized mass damper protrudes from the uppermost pin on which the caliper slides, indicating that Ford engineers encountered a resonance they needed to quell.
Another huge mass damper hangs beneath one of the urethane isolaters that connect the cab to the frame.
Moving on to the front, we find a double-wishbone suspension with a high-mount upper arm (white) and a massive aluminum lower control arm. Both are longer than those found in a standard F-150 to help produce that 6.6-inch track width increase.
Another Fox shock with the internal bypass feature is in evidence, but because it's a coil-over it can't be inverted and it can't have a remote reservoir -- not without a complete suspension redesign, anyway. In a space-limited situation such as this a motion ratio less than 1:1 is of benefit, because this shock will stroke something like 7 or 8 inches as the tire moves through its 11.2 inches of travel.
You may notice that the tire is still attached. This is the point at which my floor jack died.
The high-mount design allows a relatively small upper control arm to be used, as it's greater distance from the contact patch results in lower forces at the ball joint and pivot bushings.
A long progressive urethane bump stop resides within the coils of the front spring, and it looks like some sort of wedge-shaped mounting adpater was employed to help the upper frame mount line up with the Raptor's more steeply angled shock geometry.
Here we can see where the stabilizer bar (white) attaches to the lower arm. The shock absorber's motion ratio is lower than its mounting point on the lower arm would suggest because of the angle at which it is reclined.
The aluminum lower arm is an expensive piece, but it represents money well spent.
Just so you know who did all of this.
A dual-piston sliding caliper (yellow) handles the front braking chores and they pretty much take up all the available space. The ventilated brake rotors are 13.8-inches in diameter, but some in the industry might refer to this as a 17-inch brake system because a 17-inch rim is the smallest size that will clear the caliper. It's actually a useful way to look at it.
Now this is what a 4x4 truck tire is supposed to look like: Knobbly tires with lots of sidewall to help take the edge off all those rocks and boulders. And the sidewalls of these BFGoodrich All-Terrain KO tires have three tough sidewall plies to resist rock attacks from, well, the sides.
But how much does a mounted LT315/70R17 tire and rim weigh, exactly? After all, these things are nearly 35-inches tall -- almost a full yard.
All I have to say is this: lift with your knees.