King of the Hammers isn’t the place to “test” weak parts. That’s exactly why Jason’s Polaris RZR tube chassis build has been getting so much attention around the shop. This KOH 2025 Ultra4 4900 class build is being designed from the ground up to survive brutal rock sections, high-speed desert racing, and everything in between. This episode dives deep into the fabrication process as the Wide Open Design crew builds:
- custom front suspension components
- heim-jointed upper A-arms
- adjustable caster/camber spacers
- aluminum rear toolbox systems
- and race-ready suspension geometry
Built Around Real Race Use
One of the coolest parts of this build is the amount of adjustability engineered into the suspension system. Jason redesigned the upper A-arms to use heim joints instead of bushings, allowing the team to fine tune caster, camber, suspension geometry, and steering feel for different race environments.
Using CAD design and CNC-cut suspension brackets, the entire front suspension system was developed to work with off-the-shelf Turbo R suspension components while still giving the car race-level adjustability and strength.
CAD Design Meets Old School Fabrication
The entire chassis and suspension system was heavily CAD designed before fabrication started. Instead of hand-cutting every bracket and suspension tab, the parts were designed digitally, CNC cut on the plasma table, and then hand-fit and fabricated in-house. The result is a cleaner, stronger, and more repeatable race platform. As Adam explains in the video, the combination of:
- modern CAD engineering
- CNC manufacturing
- and traditional fabrication experience
is what makes these cars come together at such a high level.
Built for King of the Hammers
KOH is one of the toughest races in off-road racing because the terrain constantly changes. The rock sections become more brutal every lap, making suspension tuning, durability, cooling, driveline strength, and serviceability critical to surviving the race. That’s why this car includes:
- Radflo suspension
- Eibach springs
- RCV ball joints
- Raceline beadlocks
- OBOR 37” tires
- Custom Splice recovery gear
- PRP seats and harnesses
- and countless custom fabricated components
all integrated into one purpose-built chassis.
Custom Rear Toolbox & Spare Storage
Another standout feature is the custom aluminum rear toolbox system. The rear compartment was CAD designed to:
- hold spare axle shafts
- store tools
- provide quick spark plug and coil access
- package the intake and airbox cleanly
- and integrate directly with the spare tire carrier
The level of detail is what separates a race-prepped car from a simple trail build. This Polaris RZR tube chassis build is shaping up to be one serious Ultra4 build. From the suspension geometry and CNC-machined spacers to the custom rear storage system and race-ready fabrication, every part of this build was designed with one goal: Survive King of the Hammers 2025 at the highest level possible.
Questions or Comments?
We'd love to hear your thoughts or answer any questions.