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Anatomy Of A Karnivore
June 25, 2003

Inside Johnny G's radical rock crawler

John Gilleland's Karnivore can do all kinds of things with rocks that no automobile was ever expected to do. Like navigate over head-high boulders, climb sideways at impossible angles, and trek up near-vertical slopes. After competing successfully in more conventional vehicles, Gilleland went to Avalanche Engineering to work out the design for a radical new rock crawler. His new-from-the-ground-up Karnivore features a narrow fuselage that affords tremendous ground clearance while keeping the center of gravity low to improve stability. The Karnivore features a tougher-then-anvils chrome moly tube chassis and a four-link suspension rather than the more prevalent three-link suspension system.

"It's more difficult to engineer a four-link suspension than a three-link," says Gilleland, who lives in Durango, Colorado. "But the four-link system gives you an advantage in that it cures a problem you get with three-links of a 'jacking' effect, which is what happens when all of your wheels are engaged, and the tire pulling the hardest will drive the links into the side of the vehicle, tending to tip it sideways. With four links, the force pushes into the center of the vehicle, rather than to either side." Presto: more stability.

"The weight is quite far forward on this vehicle, which is what you need for extreme vertical climbs," Gilleland says. "Weight forward keeps the front end from going light on extremely steep grades and coming over backwards."

To get the weight forward, the 350 V8 is mounted well in front. The radiator is behind the seats and the transfer case is right next to you. The Karnivore has shocks that provide 14 inches of travel. "We tried 16 inches of travel on a different vehicle and it proved to be too much reaction. Fourteen inches of travel is perfect. And when you drive your right tire on a boulder, it forces the left side down, so you've got a combination wheel travel of 28 inches, with the left wheel going down and the right wheel going up."

Gilleland admits that the Karnivore was built for work, not driver comfort. "It's pretty snug inside, like the cockpit of a small airplane." He acknowledges that visibility is a problem and to improve it, he put a clear Lexan window in the floor pan, to allow vision through the floor on steep climbs.

"With a big V8 in front, it's hard to see around it. But you need V8 power to haul 3,600 pounds up a rock wall."

Gilleland notes that the structural integrity of a rock crawler comes primarily from the frame, which accounts for most of the vehicle, and a considerable amount of that hefty 3,600-pound curb weight — more than double the weight of an Indy racer, for example. But, in direct contrast to most forms of automotive competition, weight is not the enemy in a rock-crawling vehicle. Gilleland says his Karnivore performs better heavy than it does light, and he adds water to the front tires to make it weigh even more. He also specified very heavy-duty axles, which weigh at least 100 lbs more each than aluminum axles designed for the same job.

"You want weight at all four corners of the vehicle," Gilleland says. "I've seen some super-light vehicles that people built and they just hopped around. You need weight to hold the vehicle down as you climb and traverse."

The front to rear weight bias of the Karnivore is 60-40, Gilleland says, and with water in the front tires, it's more like 70-30.

One feature of the car is that the drive at front or rear can be disengaged at will. "There are some interesting things you can learn to do to manipulate the vehicle. If you're in a tight situation on a vertical ledge you can disengage the rear axle and use the front tires to pull yourself around a corner, or slide the front end into a different position to line up with a crack in a ledge and climb it."

"You can also disengage the front axle if you're pushing up against a rock, and use the front end as a pivot point to slide the rear end around." Gilleland notes that disengaging the rear axle makes the vehicle squat, which pulls it low to the ground, lowering the roll center for greater stability.

Designing a rock crawler is a challenge that must accommodate a number of parameters. The Karnivore is narrow -- with axles only 60 inches wide. "I was leery of going so small," Gilleland says. "Mine was one of the first vehicles to have a very narrow axle. But the courses are getting tight and you need to be able to get through the competition gates, and still have the maneuverability to cope with the side slopes and the verticals."

Gilleland says he hasn't formally measured the Karnivore's near-vertical grade climbing ability. But he had one experience that convinced him, and everybody who witnessed the climb, that the Karnivore is in front of the class in wall-climbing ability. "I had done a trial run in a competition at Reno where I got first place," Gilleland says. "We were coming back through Moab and came to a waterfall at the end of a trail at the end of upper Heldorado. I had never been on the trail before. Everybody else was just winching up and over this waterfall because it was so vertical. Nobody was trying to climb it.

"I didn't know any different, so I decided to climb it. It was so steep that anyone standing at the top could have reached over and tipped me -- I was balanced almost vertically. But I made it without any assistance." Gilleland estimates that the grade was at least a 75-degree slope. "Maybe 80 degrees, possibly even 82."

One trick Gilleland used in climbing the waterfall was taking the winch cable and attaching it to his own front axle and cinching it down. "That sucks the suspension tight to the vehicle and lets the suspension not react to the climb. That's an extreme situation where you need the suspension not to work.

For all other situations, the working of the suspension is everything. "We finely tune the suspension so it will dampen very quickly, on a relatively soft setting, and then the rebound will be very stiff. That way, if you hit a bump, the suspension will soak up the bump very fast but the come back will be very slow so you don't bounce. That's what allows the tires to stay on the ground rather than bouncing back off."

As for tires, Gilleland swears by the BFGoodrich® Krawler™ T/A®^KX tires that he runs on 17-inch rims. "The Krawler KX's work right. The sidewalls are right, the construction of the tire is right -- everything about it is right for this sport. I've run all the other big brands and BFGoodrich tires are the best. They're easy to work with. Other guys I know who were running on other brands tried BFGoodrich once and then switched over."

In fact in 2002, BFGoodrich tires won more major rock-crawling events than all other tires combined.

BIO
Johnny G, as he is known, perhaps to spare his fans the challenge of saying (or spelling) the word "Gilleland", has been rock crawling competitively since the sport's official birthday in the 1999-2000 season. He has won five first place trophies (in two different series), and he's leading in RCAA points this year, having won the first event of the season at Reno.

Karnivore photo courtesy Seth Markowitz/Dynatrac

Heldorado waterfall photo courtesy Edd Mangino

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