F-550 Crew Cab 203"
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The Project
This is the reference build for the OpenOverland sub-frame library — 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.
The intent is to prove the architecture in steel on one real truck, document every decision with real cost data, and release the complete engineering pack — drawings, BOM, install guide — under an open license so any builder anywhere can take it to any competent fabricator and get the same result at a fair price.
The team
Joao Correia — Project owner
Defines scope, holds the engineering and cost budgets, coordinates between engineer, fabricator, and installer. Drives the open-source release.
Johannes Dobsch — Mechanical engineer
Owns the sub-frame architecture, kinematic analysis of the zero-torsion pivot system, structural validation, and weld specification. dobschpke.com ↗
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
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