Rollin’ on 49s
I know I’ve already said this, but this rock buggy was going to be LARGE. With Rockwell axles providing the platform for this monster project, everything else had to be outsized as well. Including the tires. I needed the big and capable, so I decided on IROK 49” Super Swampers, not just because of the size, but because they give the car superior traction with their scooped lugs, blade and molded siping, and special sidewall features -- extra tough cord and cut resistant compounds. All of this would be crucial to the performance of the car. But first, I had to make sure they’d work with the whole package.
Big Tires Need Big Wheels
The IROKs would be mounted on ProComp 20x10 aluminum wheels. These seemed to be the best choice since I could CNC cut out the entire center of the wheel to allow room for the Rockwell bolt pattern. I machined the back of the wheel flat so it could accept a custom, CNC cut 1” aluminum center with the new bolt pattern. This new center attaches to the original wheel with 30 3/8” grade 8 bolts for maximum strength and security. Clearly, this process took some skill and experience, which came in large part from Brakeaway Products, an awesome machine shop that fabs up some really cool parts for street bikes and side-by-sides. Make sure to check out their website.
Rolling this beast is one thing, but being able to stop it is even more important. I figured my finished car weight was going to be close to that of a full-size pick-up truck, so I decided to buy new rotors from an F-650, which, after some machining, fit perfectly over the stock Rockwell hub. I designed a CNC cut adapter that uses eight 9/16” bolts to attach the rotor to the adapter and uses six 1” lug studs to attach the adapter to the hub. The dual piston, large bore calipers came from an F-350 and attach to the knuckle with a water-jet cut mounting bracket that I designed. With this assembly, I’d have the braking power to stop the equivalent of a fully loaded, full-size pick-up. I was confident this would be enough for the buggy. And the blue anodized adapter adds a splash of color— this car wasn’t only going to be big, but stylish, too!
With the braking under control, I figured it was time to address air pressure. Running these tires at low pressure to increase grip would be an everyday thing; they needed to be able to hold a bead, so I sent them to Trail Ready for external bead locks. Still concerned with keeping a tight seal on such a wide, tall tire, I designed a custom interior “bead lock” – it’s a cone insert fabricated out of UHMW, or Ultra High Molecular Weight plastic. It sits inside the tire and pushes on the interior bead with pressure from the outside lock ring. This system ensures that even in the most twisted, off-camber and off-balance stance, the tires would hold a bead and maintain the pressure right where I wanted it.
Phew! Tons of work (mental and physical!) had to be done to get this girl her shoes. And as I was going through the design process, I felt pretty good about my decisions. But as any designer knows, the proof is in the pudding, and (spoiler alert!), since I’ve had her out on the trail, I’ve been nothing but happy with the performance. I hope what they say is true about hard work paying off, ‘cause as much work as this build had been so far, there’d be a whole lot more to come!
Cover photo by Jami Pellegrino
Article photos by MPC