2020 Ford F-250 Tremor | Suspension Deep Dive

For as many years as I can remember, Ford Super Duty pickups have ruled the roost when it came to heavy-duty towing and hauling. Off-road performance, on the other hand, has been left to the aftermarket. Sure, there’s such a thing as an FX4 Off-Road package, but that’s pretty weak sauce. Ram has rightly been able to point at its 2500 Power Wagon and underline how much more seriously Ram takes off-road performance in the heavy-duty pickup segment.

That’s now debatable. The 2020 Ford Super Duty pickup order guide has a new line item called 17Y, the Tremor off-road package. Unlike the Ram 2500-only Power Wagon, the Tremor is available in F-250 or F-350 form, and the engine lineup goes beyond gasoline to also include diesel. Any variety of Tremor can tow and haul more than the Power Wagon, too. Quite a bit more, in some cases.

We can’t say which is better off-road until we get them together in some suitably gnarly location. But nothing is stopping me from getting a head start on that question by taking the wheels off and having a look-see in my own driveway for the latest suspension deep dive. For the record, this is an F-250 Tremor with the optional 6.7-liter PowerStroke diesel V8 engine, a distinction I'll discover actually makes a significant difference to the suspension and what extreme tasks it's best suited to tackle.

The F-250 Super Duty pickup is a no-nonsense heavy-duty machine that rides on a solid front axle that we can’t yet see. But we can see a clue that gives away its existence: a massive radius arm (green arrow) that controls its position in space.

The nose of a Tremor stands 2 inches higher than a regular F-250. A half inch of that comes from these Tremor-specific springs that sit directly atop the axle. The remaining 1.5 inch comes from the larger radius of its huge 35-inch tires — 285/75R18 in new money. Non-Tremor XLT, Lariat or King Ranch F-250s ride on 275/65R18 tires — 32 inches tall in old money.

The Tremor’s unique shock absorbers mount directly to its front axle housing (green) via this welded-on bracket. But the magic is hidden inside. These have a larger diameter that accommodates a 45-mm piston instead of the usual 35-mm one. The bigger piston makes them more sensitive to small motions, and it gives them the capacity to generate the larger damping forces necessary to control heavy off-road impacts. But the most significant benefit may be the extra oil volume that allows them to better stand up to extended running on relentless washboard roads.

Here you can see both radius arms in action. I like to draw a distinction between arms and links. Links attach at one point on each end, but arms have two mounting points (green) on one end that allows them to triangulate the axle’s position. These two arms do the work of four links.

The upside of this approach is it’s beefy and durable. The downside is the suspension’s caster angle will change as the suspension moves. This tendency becomes less significant as you make the arms longer. Also, precise caster control is less important here. This is a 4x4 truck, not a sports car.

These are twin-tube shock absorbers, but they look odd. Most shocks of this type neck down toward the mounting eye, but these bulge out. The reason is crucial to the potential off-road success of the Tremor. Inside there are hydraulic compression and rebound end stops that give them position-sensitive damping. We’re looking at evidence of the compression zone.

The end stops begin to engage during the last 20% of compression travel, which makes these shocks better able to absorb a big impact or, say, land a jump without bottoming out heavily. The ones at the rebound end that we can’t see aren’t as pronounced because full extension events must only contend with the weight of the hanging suspension, not the entire truck.

A Tremor’s stabilizer bar (green) is smaller than it would be on a regular F-250. This move improves articulation, but it also shows that the Tremor is less committed to pure boulder-hopping than the Power Wagon, which has a fully disconnectable stabilizer bar.

The Tremor’s end-link (yellow) connects to the front axle much like the shock absorber does, but the upper end of the link hides something (red) of importance.

That something is the bump stop and its landing pad (red) on the axle housing. That doesn’t look like a lot of space, but it is. I supported the truck by the axle on this side so the suspension is compressed slightly more than usual, not hanging free.

This panhard rod (red) is the fifth link that keeps the axle from moving side to side. We’re looking at the fixed end where it bolts to the frame.

The fixed end is on this end because that’s also where the Pitman arm (yellow) comes down from the steering gearbox. You don’t want these arms criss-crossing each other. The Pitman arm moves the drag link (also yellow) left and right when you turn the steering, which in turn compresses or extends the steering stabilizer (green), a shock absorber that smooths out the steering.

The drag link (yellow) attaches to the right front hub, which then transmits the signal to the left front hub through a long tie rod (green). The cool part here is how the drag link and tie rod share a common axis (white line) and pivot point. You might think this would be universal, but it’s often not the case.

The drag link is quite a bit longer than the panhard bar (red), a difference that means both will swing through different arcs. A driver might have to input a steering correction during extreme travel events.

Alignment adjustments are easy here. Loosen the drag link clamps (blue) to center the steering wheel. One side has left-hand threads and the other has right-hand threads, so you simply turn the middle part to make changes. Likewise, toe-in adjustments are made by loosening the clamps on the tie rod (black), then rotate the center section to lengthen or shorten it as necessary.

No other alignment adjustments are possible because it’s all built into the axle housing, which is set up so the center of the u-joint is precisely aligned with the steering axis. Why u-joints instead of constant-velocity (CV) joints? This is a rear-drive machine until four-wheel drive is engaged, and that’s only supposed to be done on dirt, sand or snow. The slight drive velocity oscillation that comes with u-joints isn’t an issue on loose surfaces.

OK, fine, but what’s up with that hose (green)?

This is a vacuum line that supplies the automatic locking front hub. Hubs that can be locked and unlocked used to be commonplace, and they’re still important in a truck with a massive solid front axle like this. In two-wheel drive you want your hubs to be unlocked or “free” so the u-joints we saw in the last picture (and the axles they’re attached to, as well as the front ring and pinion and the front driveshaft) aren’t being backdriven by the wheels all the time. All that represents a lot of unnecessary wear and fuel waste. Manual locking hubs were once the norm, but getting in and out of the vehicle and moving them from “free” to “locked” every time you shifted the transfer case into four-wheel drive was thought by many to be a real pain.

Auto-locking front hubs grew out of that, but the pure mechanical ones used drive torque to ratchet themselves into the locked position when 4x4 was engaged inside the cab. This was great for convenience sake, but the approach meant that they could unlock going downhill in engine braking situations. Durability wasn’t always so great, either.

These vacuum-operated auto-locking hubs get around that because engine vacuum does the job, not drive torque. When engaged, they can transmit drive torque when powering uphill or when engine braking downhill. Ford has used three variations on this theme, and this is the Constant Vacuum Hublock (CVH) design. Vacuum is automatically applied and sustained to lock the front hubs when you select four-wheel in the cab and is removed to unlock the hubs when you switch back to two-wheel drive.

I know what you’re thinking. What if the vacuum system leaks? Simple. You can get out and manually lock them like grandpa used to do. You don’t have to, but you can if needs must. Just remember to get out and manually set them back to Auto when you shift back into two-wheel drive.