Monster trucks are huge, heavy vehicles with giant tires, so turning them with only the front wheels would require a very large space. Steering both the front and rear axles lets the truck rotate more easily around a smaller turning circle. This is important in arenas, where drivers need to line up jumps, avoid obstacles, and recover quickly after stunts.
Four wheel steering also helps control a truck when the tires are bouncing, sliding, or digging into dirt.
Understanding Monster Truck Steering Both Axles
A four wheel steering system needs more than a second steering wheel. The driver turns a steering wheel that operates hydraulic valves. These valves send pressurized fluid to steering cylinders near the axles.
A cylinder pushes one way or the other and moves the steering linkages connected to the wheel hubs. Pressure equals force divided by area. This means fluid pressure acting on a large piston can create a strong push.
That strength matters because wide tires gripping rough ground resist being turned. The steering system must be rigid enough to hold the chosen wheel angle when the truck lands hard.
During a tight corner, each tire follows its own curved path. The inside wheels travel around smaller circles than the outside wheels. If the wheel angles are poorly matched, tires are forced to scrub across the ground instead of rolling cleanly.
Scrubbing wastes energy, strains parts, and can pull the truck away from the line the driver wants. In opposite phase steering, the rear axle helps the vehicle pivot near its middle. The useful comparison is simple.
With equal steering angles, the ideal turning radius can be about half the radius of a similar vehicle steering only at the front. Real trucks do not reach this perfect result because tires deform and slide.
Grip sets the real limit. A tire can create sideways force only up to the friction limit. That limit depends on the coefficient of friction multiplied by the normal force.
Normal force is the load pressing the tire into the ground. When a truck accelerates, brakes, lands, or crosses a rut, its weight shifts between wheels. One tire may have strong grip while another becomes light.
The driver must use steering smoothly because a sudden input can exceed available grip. Then the tire slides, and turning the wheels further may not make the truck turn more.
Same phase steering has a different purpose. With both axles angled in the same direction, the truck can travel sideways across the arena while its body stays pointed nearly forward. Drivers can use this crab movement to improve their approach to an obstacle or place the truck accurately after a landing.
Students should separate wheel direction from vehicle motion. A wheel points where it is trying to roll, but the truck may move at a different angle when dirt is loose.
Pay attention to wheelbase, steering angle, tire grip, and weight transfer. These factors explain why steering modes can be useful in one moment and difficult to control in the next.
Key Facts
- Opposite phase steering means the front and rear wheels turn in opposite directions to reduce turning radius.
- Same phase steering means the front and rear wheels turn in the same direction so the truck can move diagonally in crab mode.
- For a bicycle model with front steering only, R = L / tan(theta), where R is turning radius, L is wheelbase, and theta is steering angle.
- For ideal opposite phase four wheel steering with equal angles, R = L / (2 tan(theta)), so the turning radius is about half the front steering case.
- Turning torque at the tires comes from lateral friction, with F_friction <= mu N.
- Hydraulic steering systems use pressurized fluid to multiply force, described by P = F / A.
Vocabulary
- Four wheel steering
- A steering system in which both the front and rear wheels can change angle to control the vehicle direction.
- Opposite phase steering
- A steering mode where the front and rear wheels turn in opposite directions to make a tighter turn.
- Crab steering
- A steering mode where all wheels point in nearly the same direction so the vehicle moves sideways or diagonally.
- Turning radius
- The radius of the path followed by the vehicle as it turns around a center point.
- Hydraulic actuator
- A device that uses pressurized fluid to push or pull steering parts with large force.
Common Mistakes to Avoid
- Assuming the rear wheels always follow the front wheels is wrong because rear steering can actively change the truck path and rotation.
- Confusing crab steering with tighter turning is wrong because crab mode moves the truck diagonally instead of rotating it sharply around a center.
- Ignoring tire friction is wrong because the steering system can only control the truck if the tires can generate enough sideways force on the ground.
- Using front steering formulas for four wheel steering without adjustment is wrong because rear wheel angle changes the geometry and can greatly reduce the turning radius.
Practice Questions
- 1 A monster truck has a wheelbase of 3.6 m. With front steering only at 30 degrees, estimate the turning radius using R = L / tan(theta).
- 2 The same truck uses opposite phase four wheel steering with front and rear wheels both at 30 degrees. Estimate the turning radius using R = L / (2 tan(theta)), and compare it with front steering only.
- 3 Explain why a driver would choose crab steering instead of opposite phase steering when lining up with a ramp after landing at an angle.