The rally truck in 3D
A desert race truck built the Drumlin way: a steel-tube cage a home shop can MIG-weld, solid axles on long-travel links, and a 12-valve Cummins diesel with a mechanical injection pump — no computer on the fuel. The target is about the price of a new Ford Raptor in parts. It opens with the body off so the cage shows. Steer it with the slider, run the suspension through full bump, full droop and a diagonal twist, or tick the box to put the body on. A design in progress — nothing is built.
Why solid axles. The first version was a trophy truck with an independent front end, race axle shafts and a rack. Priced from published parts it came to $110,000–190,000. Solid axles and a built 12-valve come to about $95,000–115,000, which is roughly a new Raptor. The cost is top speed: this is a 70–100 mph desert truck, not a 110–140 mph one. The prices are estimates from a web search, not quotes.
Copied, not invented. The front is a three-link with a track bar, as long-travel solid-axle trucks use. The track bar sits level, and it is parallel to the drag link and the same length, so the axle can move up and down without steering itself. At each front wheel a coilover and a bypass shock, both 16 inch, stand on the axle. The rear uses 60 inch trailing arms with the shocks mounted on the lower links, the trophy-truck layout. The radiators ride in the bed, where the air is clean.
The steering. A steering box, a pitman arm and a drag link to high-steer arms, with a hydraulic ram helping. If a hose bursts, the mechanical link still steers. The slider moves the parts the way the checked model does. At full lock the inside wheel turns 33–38° and the outside wheel 29–33°, depending on the direction. Bump steer is zero when both wheels move together and 0.2° in a full twist.
The numbers. A 135 inch wheelbase, a 93 inch track and 40 inch tyres. The front axle travels 15.4 inches and the rear 20 inches. The frame and cage are drawn in 2 × 0.120 inch DOM steel tube for the Ultra4 4400 class, to be checked against the rulebook before any tube is bought. The engine, transmission and transfer case are drawn as boxes sized from published dimensions.
The weak point is the rear driveshaft. It is only about 25 inches long and runs 27° at full bump, steeper than a plain universal joint takes. It needs a high-angle double-cardan shaft, or the axle's travel needs to be split differently.
The clearance check ran through the whole steering sweep, full bump, full droop and both diagonal twists. No part passes through another. What it does not show: strength, spring rates, the brakes, the exhaust, the fire system, and the cage as it would be welded. The figures are estimates from the design, not measurements.