F-550 Crew Cab 203"
Goal
Build a verified, fabrication-ready zero-torsion sub-frame for the 2024 Ford F-550 Crew Cab with 203" wheelbase, LiquidSpring suspension, and 41" super single tires.
This is the reference build for the OpenOverland sub-frame library.
Truck
| Parameter | Value |
|---|---|
| Vehicle | 2024 Ford F-550 XLT 4WD Crew Cab |
| Engine | 7.3L Godzilla V8 Gas |
| Wheelbase | 203" |
| GVWR | 18,000 lbs |
| CA Dimension | 84.0" |
Suspension
| Parameter | Value |
|---|---|
| System | LiquidSpring FS4L active hydraulic |
| Rear Lift | 4" |
| Rear Jounce | 3.9" — critical clearance dimension |
| Rear Rebound | 4.0" |
| Kneeling Drop | 4" |
Tires
| Parameter | Value |
|---|---|
| Tire | Continental MPT 335/80R20 |
| Diameter | 41" at highway pressure |
| Width | 335mm at highway pressure |
| Minimum Pressure | 25 PSI |
| Conversion | Buckstop super single |
The tire swept volume at 25 PSI through full 3.9" jounce defines the geometric exclusion zone. No sub-frame structure enters this zone. Minimum 25mm clearance margin beyond the envelope at all points.
Mount System
Three-point zero-torsion. Statically determinate.
Front — one lateral pivot:
- Allows rotation on the lateral axis only
- Pin: 4140 chrome-moly ground shaft
- Bushing: SAE 841 oil-impregnated bronze sleeve
- Brackets: A36 steel plate — welded to sub-frame
- Adapter plate: bolts to truck frame via factory holes
Rear — two fixed mounts:
- No rotation
- One each side
- Adapter plates using factory Ford body mounting holes
Chassis drilling rules:
- U-bolt and shear plate assemblies per Ford Body Builder Guidelines
- Factory body mounting holes only — no new flange holes
- LiquidSpring web drilling: Ø21/32" — web only — per installation manual
Key Constraints
Deck height: Maximum 5" above frame rail top surface. Hard limit.
Tire clearance: All structure outside the swept volume envelope with 25mm margin. No exceptions.
Chassis mounting: No new holes in top or bottom frame flanges under any circumstances.
Structure
- Main rails: ASTM A500 Grade C HSS — size per engineer
- Crossmembers: ASTM A500 Grade C — regular spacing
- Outriggers: extend beyond main rails for body attachment
- Adapter plates: ASTM A36 plate
AWS D1.1 certified welders required. Full penetration welds at all primary joints. All welds inspected before coating.
Built-in Provisions
- DOT air line routing — 1/4" OD PA12 nylon — P-clip mounted every 12-18"
- Two air outlets mid-frame — one each side — 1/4" NPT for Milton S-1750
- License plate bracket — centered rear
- Wiring conduit provisions for tail lights and body electronics
Coating
- Blast clean to bare metal — Sa 2.5
- Mask all bolt holes, threads, mounting surfaces
- Line-X applied directly to bare blasted steel
Build Team
| Role | Name |
|---|---|
| Project Lead | João Correia |
| Chief Engineer | Johannes Dobsch — dobschpke.com |
| Fabricator | TBD |
| Contributors | — |
Changelog
| Version | Date | Description |
|---|---|---|
| v0.1 | 2026-04 | Initial specification — truck, suspension, tire, and mount system defined |
Reference Documents
- Ford Body Builder Layout Book — 2024 F-450/F-550/F-600
- LiquidSpring Installation Manual — D12348 FSeries FS4L Rev AH
- LiquidSpring Tear Sheets — MK5227, MK5034