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Carli Suspension | FORD SUPER DUTY LEVELING LEAF SPRING LOAD TEST

The Carli Deavers – they’re synonymous with the elusive “buttery” ride quality touted by Carli-equipped HD enthusiasts. With this rear compliance comes capacity degradation. It wasn’t much to talk about when we started offering our version of the Deaver Spring; you remember… back in the day that a 3/4-ton carried, well, 3/4’s of a ton and a 1-ton, 1-ton. Reduction in hauling capacity for these trucks would drop them from a respectable 1,500/2,000lbs closer to the 1,000-1,200lb area.

New truck capacities have gotten out of hand. The new F-250 boasts a whopping 2,462lbs – 4,323lbs in bed capacity, depending on configuration. The Carli Deavers, well, they’re still hanging their hat on good ol’ “Light 3/4-ton Capacity.” Deaver has always shied away from throwing a number at it for the same reason Ford varies about 80% within the same platform: it’s motor, cab and configuration dependent. In most applications, this is a non-issue. We’ve been making Long-Travel airbags to supplement our reduced capacity springs back to factory capacity nearly as long as our springs have been available.

Unfortunately, there are a couple applications for which we don’t make a load supplements but offer reduced capacity leaf springs; namely, the 2014+ Ram 2500 and 2011+ Ford Super Duty in the Leveling configuration. For these, we load-test them and provide customers the data to ensure the products will suit their applications. This test is on the L18 Spring or, as you all know it, the Leveling Leaf Spring (FFSP-LVL) for the 2008 to 2021 Super Duty!

Measurements Taken:

Center of Hub to Fender-Lip: This measurement is “rough”. When measuring from an approximated “center of hub” around a tire to a tapered fender flare with a round lip, one cannot expect precision but it’s plenty-good to understand the points portrayed within. This eliminates tire-size from the equation but adds a large margin for error so take this measurement with a grain of salt. Namely, it’s here to confirm what you measure at the bump stop while giving a rough idea of how the body-lines will look when loading.

Axle to Bump Stop: This is a FAR more precise measurement. It isolates the suspension (Unaffected by body-mounts, tires/pressures, etc). This is the ideal measurement to take when determining rear sag but it doesn’t provide the “perspective” view the body-line will; this the center of hub we’re including.

Something to consider in the axle to bump measurement – the bottom of this bump stop isn’t the end of your travel; it’s designed to slow travel and can compress fully. The length of these bump stops is 3.5″ – this length is ALL functional travel. Other manufacturers (RAM, for example) use extremely hard durometer jounce-stops that are much shorter and sharper when encountered. The Super Duty bumps are a far better, albeit larger, design that sooner for a more progressive, softer engagement.

Given their design and size, they make travel appear FAR shorter than it actually is. A measurement of 2.5″ from the axle tube to the bottom of the yellow-bump is actually a measurement of 6″ (3.5″ bump-zone + 2.5″ gap) of total rear up-travel.

UNLOADED

1/2″-1″ Rear High | (Measured at the Fender)

We removed everything from the bed. A factory Spare wheel/tire is installed.

6″ Effective Up-Travel, Including Bump Stop

  • Center of Hub to Fender Lip, Front: 27.5″
  • Center of Hub to Fender Lip, Rear: 28″
  • Axle to the Bottom of the Bump Stop: 2.5″


500lbs. Bed-Load

Level to 1/2″ Rear Low | (Measured at the Fender)

We evenly distributed (5) 98lb. Coil Spring Product boxes on the bed-floor. A factory Spare wheel/tire is installed.

5″ Effective Up-Travel, Including Bump Stop

  • Center of Hub to Fender Lip, Rear: 27.25″
  • Axle to the Bottom of the Bump Stop: 1.5″

1,500lns. Bed-Load

1″ Rear Low | (Measured at the Fender)

We evenly distributed (5) 98lb. Coil Spring Product boxes on the bed-floor, then added (6) 82lb. Coil boxes. A factory Spare wheel/tire is installed.

4.5″ Effective Up-Travel, Including Bump Stop

  • Center of Hub to Fender Lip, Rear: 26.75″
  • Axle to the Bottom of the Bump Stop: 0.75″


Wrap-Up

So now you’ve seen them in action – what does this all mean to you, the customer? I personally drove this truck around with 1,000lbs in the bed over several hundred miles. This is the MAX bed-load with which I would personally feel comfortable driving long distance. 1,500lbs was definitely doable, and controlled, but hovering the bump stops is less than ideal.

Again, this is load testing our standard Full Progressive Leaf Spring Packs. These are, by FAR, our most popular rear option. We have several other options I will detail later in this article.

The standard Full progressive leaf springs are best suited to those seeking the most compliant possible ride quality that spend most of their time unloaded. When loaded, they’ll handle up to 1,000lbs. in the bed, or an equivalent trailers (for example: wakeboard boat trailers, normally around 500lbs. tongue weight on the high side), with ease. This can be pushed a bit on just the leaf springs BUT supplementary products are available for those after the best unloaded ride and max capacity.

To be clear, the following products are NOT Carli Suspension manufactured or tested. They’re parts that have been reported by customers and retailers to have successfully supplemented them back to factory payload capacity with our leaf springs installed. You’re best to discuss the Pros/Cons of each with your retailer but I’ve outlined the highlights here.

Timbren SES Suspension: These hollow-rubber springs replace your factory bump stops hovering the axle 0.50″ to 1.5″. When they hit the axle, they hold the load. As these rubber springs are designed to hold a load, they will eliminate MOST of your up travel in favor of their “spring rate” assisting the suspension in handling the load. We recommend swapping these in ONLY when hauling/towing or you’ll be bouncing off them over every little bump in the road.

These are ideal for the customer Hauling a few times a year that doesn’t mind spending 20 minutes to swap the bumps for the Timbrens on the rare occasion they’re needed.

Airbags: Double-bellow airbags are not something we normally recommend. They’re the reason we developed our own long-travel airbag system. These bags give up travel, ride miserable unloaded and limit the rear end to 4-5″ of suspension travel. That said, you can combine the following:

  • A double-bellow airbag kit
  • 2-wheel drive lower bracket: connects to the axle vs. the bump stop tang as the block from which this protrudes is eliminated with the removal of the factory block
  • A spacer to make up the distance of the removed block
  • A daystar cradle to allow the axle to disconnect from the bag on droop

The above becomes an erector-set passable for those requiring frequent inflation/deflation for varying loads and minimal fuss.

Other Rear Options for MORE Capacity

Progressive Add-a-Pack

2011-Current Progressive Add-a-Pack Shown

This “mid-pack” replaces the overload spring on your factory leaf pack. The overload spring is the thick leaf at the bottom that doesn’t follow the contour of the rest of the leaf-pack. It’s a “ceiling” for the rest of the springs, so to speak.

Factory Overload Spring highlighted in RED

it determines where the back of the truck will sit when loaded BUT the capacity of the truck comes from the main spring pack – the two leaf springs shown above the overload – NOTE: F350s will have 3 main springs. As the main spring pack remains unmodified and the “ceiling” is removed in favor of the pictured assembly of leaf springs, the engagement and disengagement of the modified factory leaf springs becomes substantially more predictable. One can expect a bit more sag when loaded, a better loaded ride, better off-road performance and better overall traction.

As a rule, an F250 will see a better unloaded ride with the add-a-pack. An F350 has an extra main leaf in the pack (3 main leaf springs vs. 2 in the 250) and is MUCH stiffer than it’s 250 counterpart; for this reason, the add-a-pack will not help the unloaded ride – it may even stiffen it.

Compared to the Full Progressive Leaf Spring replacements (the ones tested in the above article), the add-a-packs will tow and haul better BUT this will be at a cost of ride quality and articulation both on and off-road.

HD, XHD & XXHD Leaf Spring packs

And so we enter the Carli Progressive Leaf Spring rabbit hole. In our years developing suspensions for the Super Duty Trucks, we’ve seen just about everything. As we’ve grown, the custom builds we’ve done have overlapped others; the resulting products developed for these custom applications have become “secret menu” production.

NOTE: All the the springs discussed below are CUSTOM for trucks with full-time loads. They’re NOT for people that occasional tow/haul. These customers are best setup with our standard full springs and a load supplement to avoid the super-stiff unloaded ride that accompanies an unloaded, over-sprung truck.

Leveling HD Leaf Spring packs

NOTE: Pictured is a 4.5″ but it’s a perfect example of an “HD” load with the Roof-Top Tent, Custom Rack and another 500lbs of gear in the bed.

As discussed above, the standard Carli Leaf Springs will haul 1,000lbs with ease. That said, what if you built your dream truck and it happens to include a Camper Shell and Loaded bed-slide with a full-size 37″ Spare strapped to it adding around 1,000lbs of constant weight to the back of the truck? The standard Carli springs will “handle” this load but they’re not setup to operate with the additional 1,000lb. baseline.

Born from necessity, we created the “HD” progressive leaf spring pack. This pack will perform EXACTLY as our standard full springs will but with a constant 800-1,200lb. bed-load. Originally, these were created for a customer in Austin, Texas with, well, exactly the above configuration. Over the years, we’ve sold these to oil-patch customers with tool-boxes/fuel boxes, Overlanders with custom Bed-Racks, Roff-Top-Tents, and toolboxes, etc. They’re actually listed on the website they’ve become so popular.

As they’re a mild-increase in spring rate, they can be used with Carli Backcountry and Pintop Shock Packages without any additional tuning required.

Leveling XHD Leaf Spring packs

As the “Overland” Market has grown, and with it, the different in-bed camper segments, we’ve found ourselves adapting. The “HD” spring can be pushed from it’s recommended 1,000lbs. but not by much. Plus, if you’re spending that kind of money on a custom spring pack, why settle for “almost” correct? We started with the TFL Truck. If you’re unfamiliar with them, The Fast Lane Truck is a popular YouTube truck-testing channel. We participated in the build of their 2020 F250 they equipped for their “No Pavement Needed” series in which they took a Carli Pintop equipped Super Duty across the country with a 4 Wheel Camper Hawk pop-up in the bed supported by our “XHD” leaf spring pack.

The constant 1,800lb.-2,000lb bedload required us to build a beefier version of the HD leaf springs. With this leaf spring and the added spring rate, we require customers to run the Pintop (King 2.5″) shock package for which we’ve developed a custom shock tune refining the overall ride, handling, spring rates and heightened center of gravity that accompany a rig modified as such. The result can be seen in the MANY videos TFL published featuring this bad-ass rig.

Availability on these, you’ll want to reach out to your Carli Retailer – be aware, they may not even know they exist. That said, you can expect a custom order to be in the 2-3 month range which matches a normal (non-COVID) lead time on the matching, custom tuned King Shocks to accompany them.

Leveling XXHD Leaf Spring packs


Overland with a large cab-over camper or build an off-road rescue rig, these XXHD leaf springs support a 3,500lb. constant bed-load. Custom designed originally for the guys at Motorsports Safety Solutions, these leaf springs bolster the SRW F350’s max bed-load capability into a working load capacity that’s huge on travel and fully progressive. The truck for which they were built scaled at 11,740lbs (5,400 front, 6,340 rear).

Developed for the massive, flagship, off-road race-rescue truck, we’ve sold these springs to many customers with custom flat-beds and large, fixed campers. So long as you’re around the 6,500lb. rear axle weight (confirmed on certified scale), these will be the perfect means of suspending your adventure rig!

As with the XHD springs, these will have a custom-order lead time AND require custom tuned Pintop Shocks (different tuning than the XHD shocks) to support the massive spring rates and load capacity of these springs.

In Closing…

As evidenced above, we’re now the Baskin-Robins of Ford Super Duty Leaf Spring Systems. It’s safe to say, no one has spent the time we have to perfect these “niche” market segments. Give us a call, drop a comment on here or shoot us an email – we’re happy to go as in-depth as you’d like on any portion of this article and how best to setup YOUR dream build!

Need help? We're available at208.719.7400 - Email us atsales@alligatorperformance.com orlive help
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