The off-road truck (Sometimes referred to as a "Trophy truck") is a specialized off-road racing vehicle that resembles a pickup truck. It is an offshoot of the original dune/off-road buggies used in the US Southwest and Baja Mexico, and shares many characteristics with them.
The off-road truck is characterized by a tube frame chassis with a high horsepower engine mounted at the front which drives either the two rear or all four of the wheels. The suspension is built with long travel and is relatively softly sprung to absorb large bumps, dips and jumps the truck travels over at high speeds. The chassis is covered with composite bodywork and usually uses the space normally associated with a pickup truck bed for the storage of spare tires and support equipment.
Racing events are held on dirt roads and on desert, wooded, and other natural terrain with the most well known races happening in the Mexico (Baja) and Africa (i.e. The Paris-Dakar).
Off-road Truck Contents
|Power and Weight Stats|
|Horsepower (Typical Range)||500-800|
|Race Weight (Typical Range)||1679-2724 kg
Design and Construction
Race Car Models of This Type
Build Your Own Off-Road Truck
Due to the scratch-built nature of off-road trucks, the designer should be knowledgeable in handling, chassis, suspension, powertrain, aerodynamic and safety design. These six major areas of the truck design work as an integrated unit and the designer must have an understanding of how changes to one area affect the others. Much of the design work is iterative, meaning re-designing areas based on new changes to another area. After the iterations are completed, the design will be complete and optimized.
Because of the varied environments where off-road trucks can operate, knowledge of the terrain is important to ensure the vehicle will handle the demands of the surface and speed.
Weight Distribution: Typically the front will be heavier in front/rear weight distribution due to the front-engine configuration. Left/right weight distribution will ideally be 50/50 to provide predictable cornering.
Suspension: Maximizing the contact patch of the tires with good suspension geometry is of key importance. Because of the long suspension travel there can be significant camber change. Some camber may be of benefit in cornering, but excessive camber will likely mean less traction. With a soft independent front suspension, body roll can be controlled through anti-roll bars.
Suspension, wheel and tire weights (Unsprung weight) affect the compliance of the suspension, which in turn affects handling, so keeping all these components as light as possible is an advantage. However, due to the requirement for durability over many miles of rough terrain, it is also difficult in practice. Springs and dampers (shock absorber) must be matched to the suspension geometry and calculated forces.
Rear suspension designs on off-road trucks generally utilize either independent or 3/4-link live axle configurations. Independent suspension a-arm lengths are usually very long (mounting almost at the lateral center of the vehicle) to minimize camber changes.
The suspension pickup point locations impact the chassis design.
Chassis: off-road truck chassis are built using spaceframe design to minimize weight and maximize structural rigidity for predictable handling. Designing torsional rigidity into the chassis will avoid twisting the chassis and any undesirable handling behaviors that result.
Powertrain: Weight distribution is heavily impacted by engine position, and both front and mid-engine designs have been created. Intake, Cooling and exhaust need to be considered in relation to chassis design, bodywork and aerodynamics, especially when operating in hot, sandy environments.
Aerodynamic: Gains in the reduction of drag generated by an off-road truck might be significant enough especially on long high-speed stretches to consider shaping of bodywork to reduce drag. Cooling and exhaust might also be incorporated into such a design.
Safety: Providing a substantial crash/rollover safety cell for the occupants is vital along with racing seats and racing harnesses. Protection for fuel storage, fire protection, and front/side impact protection are recommended if not mandatory in racing.
If you intend to race under a sanctioning body, always read and understand the regulations of your chosen racing class before designing or building any race vehicle.
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Ensuring the chassis is dimensionally accurate and straight is important as flaws in the structure will create handling issues via misaligned suspension. The use of a solid, flat and level build space is important. Jigs are often used in this case to ensure that structural tubing stays in alignment during welding/brazing.
The builder should have solid joining and metal working knowledge and skills when fabricating the chassis/rollcage/suspension. While mild steel (1018/1020) is very forgiving, some metals are best welded using a specific method (mig/tig) and some require heat treatments before and following welding to restore their toughness and strength.
Many suspension and powertrain components for an amateur-built off-road truck can be sourced as off-road aftermarket parts. This will lower the overall cost. The spaceframe chassis design of these vehicles means their weight is considerably lighter than a production truck. So for instance, suspension components originally designed for a full-size pickup truck will likely be very durable.
A consideration for those wishing to build a competitive vehicle on a budget might be to spend more money on racing oriented adjustable, lightweight and yet very durable suspension components (springs, shocks, uprights/hubs, brakes, wheels), and go more aftermarket on components that are sprung (ie. not attached to the suspension).
Because the off-road truck is scratch-built, there will be significant effort in design and construction. The off-road truck has the largest, most detailed chassis of amateur-buildable vehicles and the largest suspension and powertrain. The bodywork is also large relative to most other race vehicles.
There is however, an equally great satisfaction and sense of accomplishment at being one of the few people in the world who have built their own race truck from the ground up!
Tires and fuel probably form the single largest consumable expense along with engine rebuilds and suspension part replacements. A dirty or gritty working environment will usually translate into parts wearing out sooner.
Transportation and Support Equipment