This is the Proving Grounds Racing truck #4570, competing in the 4500 class at this year’s King of the Hammers off-road race. It’s based on a Jeep Wrangler Unlimited TJ/LJ chassis. (Image/Proving Grounds’ Facebook Page)

The 2021 edition of the King of the Hammers has been underway for about a week now in Johnson Valley, California. The annual competition spans several days, culminating in the main event this Saturday: a grueling 90-mile off-road race that combines high-speed desert runs with precise, technical rock climbing.

Among this year’s entrants is veteran off-road racer John Grounds and his Proving Grounds Racing team. The team is comprised of skilled mechanics, vehicle builders, and off-road racers with years of experience competing in the King of the Hammers and similar events—racking up plenty of podium finishes in the process. The team is fielding a pair of vehicles in this year’s competition.

So let’s take a quick look at the trucks and get a better understanding of the King of the Hammers event.

For starters, there are several different vehicle classes that compete in the King of the Hammers. As mentioned above, Proving Grounds prepared two vehicles for 2021: one races in the 4400 class and the other in the 4500 class.

The 4500 Modified Class means the vehicle has to use a modified OEM or OEM-style chassis, and feature mechanical steering. These trucks must run a pair of 2.5″ diameter shocks on each corner and 37″ DOT-approved tires.

The 4400 Ultra4 Unlimited Class is the granddaddy of ’em all. These trucks must use a transfer case with 4-wheel drive capability, and meet a strict checklist of safety standards. Other than that, pretty much anything goes: no limits to chassis/frame, tire size, engine type, axle, or suspension design.

Here are the Proving Grounds Racing off-roaders, numbers 4570 and 4415, alongside a Jeep Wrangler support vehicle. (Image/Proving Grounds’ Facebook Page)

Proving Grounds’ 4500-series truck, number 4570, is based on a Jeep Wrangler Unlimited TJ/LJ. The 4400-series truck, 4415, boasts a custom-made Miller Pro Chassis that you can watch come together on the 4415 progress page here.

4415 was pretty much built from the ground up. The chassis was assembled from a weld-together kit, and all of the plumbing and electrical work was custom-installed. And while 4415 features a lot of one-off custom fabricated components, the truck is outfitted with some familiar names too, like Wilwood Brakes, BFGoodrich tires, and Fox Racing Shox Shocks.

The team has been in Johnson Valley, California for over a week now, testing, tuning, and pre-running the course. Long days and short nights are the norm. (Image/Proving Grounds’ Facebook Page)

If you’re new to this sort of off-road racing, it’s really fun to watch. And you can get an idea of how exciting it is simply by looking at the vehicles—they’re part rock crawler, part dune buggy, and part stadium truck.

And what’s cooler is that you can watch the King of the Hammers events streaming live online at Ultra4 Racing’s website. And you can get updated King of the Hammers race results there too.

Here, Proving Grounds truck #4415 poses with Chuck Crossland‘s 4800-class racer #4869 and its twin-turbocharged LS engine. (Image/Proving Grounds’ Facebook Page)

And though we’re cheering on Proving Grounds’ efforts, we’re really rooting for the entire event, and all its entrants and attendees. King of the Hammers and related off-road racing is an awesome category of motorsports that we’re hoping continues to grow and evolve.

The main King of the Hammers race is slated to begin Saturday at 8 am PT, but make sure to check for date/time updates at the official race week schedule from Ultra4 Racing.

Author: Paul Sakalas

Paul is the editor of OnAllCylinders. When he's not writing, you'll probably find him fixing oil leaks in a Jeep CJ-5 or roof leaks in an old Corvette ragtop. Thanks to a penchant for vintage Honda motorcycles, he spends the rest of his time fiddling with carburetors and cleaning chain lube off his left pant leg.