Carli HD Full Progressive Rear Leaf Spring Kit | +1,000 lb Constant Load | 1" Rear Lift | 4.5"/5.5" Lift System Compatible | Carli Shocks Required | 2017–2023 Ford F-250 / F-350 Diesel 4WD | SKU: CS-FFSP-17-HD
Couldn't load pickup availability
Before ordering, verify your vehicle details, current setup, and SKU with OFAS fitment support so your upgrade matches your build.
Shipping & Delivery
Free shipping is available within the lower 48 U.S. states. Large or heavy items may ship by freight, and delivery timing can vary by warehouse, carrier, and product availability.
Fitment, Shipping & Product Support
Verified Fitment
This spring kit fits the 2017 through 2023 Ford F-250 and F-350 with a diesel engine, 4WD, and a 3.5"–4.0" axle tube. It is designed for trucks already running or planning a Carli 4.5" or 5.5" suspension lift system and carrying a constant 1,000 lb bed load. It is not a standalone load-improvement accessory and is not compatible with off-the-shelf shock valving.
| Year Range | Make | Model | Drivetrain | Engine | Axle Tube | Notes |
|---|---|---|---|---|---|---|
| 2017–2023 | Ford | F-250 Super Duty | 4WD | Diesel | 3.5"–4.0" | 4.5"/5.5" Carli lift required |
| 2017–2023 | Ford | F-350 Super Duty SRW | 4WD | Diesel | 3.5"–4.0" | 4.5"/5.5" Carli lift required |
Axle tube specification: This kit requires a 3.5"–4.0" axle tube diameter. Confirm your axle tube size before ordering — this is a hard fitment gate.
2024–2026 fitment: Carli's product page title states "17-26" but the fitment specification box states "2017-23." This discrepancy exists on Carli's own page. Text (469) 407-7538 to confirm 2024–2026 fitment before ordering.
Verify fitment by text: (469) 407-7538
Does NOT Fit
| Exclusion | Reason |
|---|---|
| 2016 or earlier Ford F-250/F-350 | Different suspension generation — prior platform uses different spring specifications |
| Trucks on Carli 2.5" leveling systems | This is the 4.5"/5.5" lift spring. The leveling system equivalent is CS-FFSP-LVL-17-HD — a different SKU with different geometry |
| Trucks with stock-height suspension | These springs are tuned for Carli 4.5"/5.5" lift geometry. Installing on a stock-height truck will produce incorrect spring rates and unintended ride height changes. |
| Trucks without a constant ~1,000 lb bed load | This is an HD spring rated for constant 1,000 lb bed load. Without that load, the truck will sit high and ride excessively stiff. The standard Carli progressive leaf spring (CS-FFSP-17) is correct for trucks without constant heavy loads. |
| Trucks using non-Carli shocks | Carli explicitly states these springs "DO NOT work well with off-the-shelf Valving." The springs require Carli custom-valved rear shocks. |
| Gas-powered F-250/F-350 | Confirmed fitment is Diesel only. Confirm gas engine compatibility before ordering if applicable. |
| F-350 DRW (Dually) | DRW rear axle and spring configuration differs from SRW — not confirmed for this SKU |
| F-150 | Not applicable — F-150 uses independent rear suspension or different leaf spring setup |
| Trucks with axle tube outside 3.5"–4.0" range | Axle tube spec is a hard fitment gate — confirm axle tube diameter before ordering |
Verify fitment by text: (469) 407-7538
Component Specifications
| Specification | Detail |
|---|---|
| SKU | CS-FFSP-17-HD |
| Kit type | Full progressive replacement rear leaf spring pack |
| Load rating | +1,000 lb constant bed load |
| Rear lift | Approximately 1" rear high stance on matching 4.5"/5.5" Carli lift systems |
| Spring design | Block-eliminating full progressive pack — 9-leaf main pack, 3-leaf progressive overload |
| Required shock valving | Carli custom-valved rear shocks — not compatible with off-the-shelf shock valving |
| Lift system compatibility | Carli 4.5" and 5.5" suspension systems only |
| Tire fitment | 37" with max 9" wide wheels and 5–5.5" backspacing |
| Includes | New U-bolts and rear bump stop drops |
| Axle tube requirement | 3.5"–4.0" axle tube |
| Engine | Diesel |
| Drivetrain | 4WD |
| Unit weight | 317 lb |
| Price | $2,474.00 |
| Prop 65 | Confirmed |
What Is and Is NOT Included
Included:
| Component |
|---|
| Full progressive HD rear leaf spring pack (pair) |
| New U-bolts |
| Rear bump stop drops |
Not Included:
| Item | Notes |
|---|---|
| Carli custom-valved rear shocks | Required — these springs do not work correctly with off-the-shelf shock valving. Must be paired with Carli's custom-tuned rear shocks for the 4.5" or 5.5" system. |
| Front Carli suspension lift system | The 4.5" or 5.5" Carli front lift system must already be installed or purchased alongside this kit. This is a rear component for an existing or concurrent Carli lift build. |
| Professional installation labor | Shop installation required. Not included. |
6. Critical Compatibility
| Condition | Interaction | Action Required |
|---|---|---|
| Off-the-shelf shock valving | Carli explicitly states these springs DO NOT work well with non-Carli shock valving. The spring rate and progression are tuned around Carli's custom piston and valving profiles. Installing these with generic shocks will produce poor ride quality and inadequate damping. | Must be paired with Carli custom-valved rear shocks for the 4.5" or 5.5" system. |
| Constant 1,000 lb bed load requirement | These springs are designed around a permanent 1,000 lb constant bed load — overland rack system, contractor equipment, camper shell, or equivalent. Without that load, the truck will sit higher than intended and the spring rate will be too firm for the unloaded condition. | Confirm your application involves constant 1,000 lb bed load before ordering. |
| Carli 4.5"/5.5" lift system requirement | The spring geometry is calibrated for the axle position at 4.5" or 5.5" of front lift. Installing these on a 2.5" leveled truck or stock-height truck produces incorrect geometry. | Confirm the front Carli lift system is 4.5" or 5.5" before ordering this spring. |
| CS-FFSP-LVL-17-HD vs. CS-FFSP-17-HD | These are two different springs. CS-FFSP-LVL-17-HD is the HD spring for 2.5" leveling systems. CS-FFSP-17-HD (this SKU) is the HD spring for 4.5"/5.5" lift systems. Ordering the wrong one for your front lift height produces incorrect rear geometry and stance. | Confirm your front lift height is 4.5" or 5.5" — not 2.5" — before ordering this SKU. |
| Axle tube diameter | Fitment requires a 3.5"–4.0" axle tube. Trucks outside this spec may not have correct mounting geometry for this spring pack. | Confirm axle tube diameter before ordering. |
Installation Notes
Skill level: Intermediate to advanced. Full rear leaf spring pack replacement is a major rear suspension job — not a bolt-on shock swap. A qualified shop with heavy-duty truck experience is required.
No front alignment required: Rear leaf spring replacement does not affect front alignment geometry. Confirm with your installer, but front alignment is not typically required after rear-only leaf spring work.
U-bolts and bump stop drops included: All required hardware for the spring replacement is included. No additional mounting hardware needed for a standard installation.
Critical — shock compatibility check: Before installation, confirm that the Carli custom-valved rear shocks for your 4.5" or 5.5" system are already installed or will be installed simultaneously. Do not install these springs with factory shocks or aftermarket shocks that are not Carli custom-tuned.
Weight handling: At 317 lb this kit requires a vehicle lift and proper support equipment. Do not attempt rear spring replacement without appropriate lift equipment.
Required tools:
| Tool | Required |
|---|---|
| Vehicle lift rated for F-250/F-350 | Yes |
| Torque wrench | Yes |
| Full socket and wrench set | Yes |
| Spring removal/installation equipment | Yes |
Torque specifications: Follow Carli's published torque values for U-bolt and shackle hardware.
Common Questions
Why does my Carli 4.5" lift system need specific rear leaf springs?
Standard rear leaf springs — factory or generic aftermarket — are not calibrated for the axle position and shock travel that a 4.5" or 5.5" Carli lift system creates. Carli designs their full progressive spring packs to work with their specific custom shock valving, rear suspension geometry, and expected wheel travel at that lift height. Mixing Carli's extended-travel rear shocks with factory or off-the-shelf springs produces a system where neither component is operating in its intended range.
What is the difference between CS-FFSP-17-HD and CS-FFSP-LVL-17-HD?
Front lift system compatibility. CS-FFSP-LVL-17-HD is for 2.5" leveling systems — it provides approximately ½" rear stance with Carli leveling setups and is rated for 1,000 lb constant load. CS-FFSP-17-HD (this SKU) is for 4.5"/5.5" lift systems — it provides approximately 1" rear high stance on those systems and is also rated for 1,000 lb constant load. The spring rates and geometry are calibrated for the axle position at each respective front lift height. Ordering the wrong SKU for your lift height produces incorrect rear geometry and stance.
My truck is a constant hauler — tools, equipment, overlanding gear. Does this fit my build?
Provided you have a Carli 4.5" or 5.5" front lift system, Carli custom-valved rear shocks, a constant approximately 1,000 lb bed load, and a diesel 4WD with a 3.5"–4.0" axle tube — yes, this is the correct spring for that build. Text (469) 407-7538 with your full setup for confirmation before ordering.
Can I run this spring on a stock-height truck to handle heavy loads?
No. These springs are tuned for the axle position and suspension geometry at 4.5"/5.5" of front lift. Installing on a stock-height truck will not produce correct spring rates, geometry, or ride height.
What is the warranty?
Carli provides a limited lifetime warranty against manufacturing defects to the original purchaser, with proof of purchase at Carli's retail price required.
The Obsidian Take
This spring kit is for the 2017–2023 Ford F-250 or F-350 Diesel owner running a Carli 4.5" or 5.5" front lift system who carries a constant approximately 1,000 lb bed load — overlanding rack and gear, contractor equipment, camper shell or equivalent — and needs the rear spring calibrated for that load rather than the standard progressive pack.
It is not a standalone heavy-hauling upgrade for stock or lightly lifted Super Duties. It is not compatible with generic shock valving. And it is not the right SKU for trucks running a Carli 2.5" leveling system — that application takes CS-FFSP-LVL-17-HD. The lift height determines the spring, not just the load.
At $2,474 and 317 lb, this is a significant rear suspension commitment. Buying it without a Carli 4.5" or 5.5" front system already in place — or already ordered — is buying the wrong part.
Manufacturer Data Disclaimer
Specifications are sourced from Carli Suspension product documentation and authorized distributor data. Actual product specifications, fitment, required companion components, and year range may vary by specific vehicle configuration, axle tube diameter, and manufacturer updates. Confirm all vehicle specifications with Carli Suspension or OFAS before ordering.
Prop 65 Warning
WARNING: This product can expose you to chemicals known to the State of California to cause cancer and reproductive harm. For more information, visit www.P65Warnings.ca.gov.
Non-Returnable Notice
Suspension components are non-returnable once installed. Confirm model year (2017–2023), drivetrain (4WD), engine (diesel), axle tube diameter (3.5"–4.0"), front lift height (4.5" or 5.5" Carli system), shock compatibility (Carli custom-valved only), and constant bed load application before ordering. Text (469) 407-7538 with any fitment questions before your order is placed.