At first glance, the two top classes in the Lucas Oil Off Road Racing Series are very similar. Even the names only differ by a number – Unlimited 2 and Unlimited 4. The numbers, as you might have guessed, refer to the number of driven wheels. The differences beyond that are a matter of rules – closed (U2) vs. open chassis design (U4), weight and a few dimensions.
Unlimited 2 trucks are based on a spec chassis, with pickup points and suspension geometry determined by the rules. Unlimited 4, on the other hand, is a completely open class. The U4 trucks can be wider, but are also heavier, weighing a minimum of 4000lb. and at least 10lb. per cubic inch of engine displacement. U2 trucks must weigh at least 9.7lb. per cubic inch with a minimum of 3750lb. Aside from those differences and, of course, the drivetrain, the two types of truck are very similar.
To the spectator watching the trucks on the track, the differences are subtle. Close observation will reveal how much more the two-wheel-drive truck slides around in the corners, or how much quicker the U4 truck scoots out of them. Otherwise, they both seem capable of insane acceleration thanks to their approximately 900hp engines (although there are no limits to horsepower, 700-900hp is typical) plus mind-boggling flights off of jumps and controlled landings thanks to a foot-and-a-half of suspension travel.
To the driver in the cockpit, though, the differences are even more noticeable and critical to success.
“The driving technique's completely different,” says Carl Renezeder, driver of the No. 1 Lucas Oil Ford in U4 and the No. 17 Lucas Oil Ford in U2 – and the current points leader in both classes. “The two-wheel drive you're steering with the brakes and throttle, driving with the rear of the truck. You're sliding the truck a lot more. With four-wheel drive, with the front wheels pulling, it innately wants to push, so the acceleration and entry to the corners are a lot different. It's a combination of using momentum and power to get the four-wheel drive around the corner efficiently so it doesn't push. If you use the accelerator at the wrong time, it'll just go straight. The tricky part is when you have to drive them back to back.”
That's a situation that Renezeder, who has multiple Championship Off Road Racing titles – three in Pro 4, two in Pro 2 – and a couple of Baja 1000 victories to his name, often finds himself in during a race weekend. Between two sets of practice, qualifying and racing in both categories during a weekend, he's bouncing back and forth a lot.
“Over the years I seem to get better at it. If the track doesn't have a lot of traction, it gets tougher to go particularly from four to two,” Renezeder explains. “I program myself when I'm in the four-wheel drive to think differently. I try to focus more on driving with the front end of the truck with the 4, where with two-wheel drive I'm more concerned with the back of the truck. I can't exactly explain how I program myself because I've been doing it so long, but definitely when I strap into each truck they're two totally different animals.”
There's even a difference when the truck is in the air, says Renezeder. He explains that it's possible to change the attitude of the truck while it's in the air – which can sometimes be as long as 150 feet – using the throttle and brake. The centrifugal forces of heavy spinning wheels and tires affects what the truck is doing in the air, and how it lands. That effect differs if you have two wheels spinning under throttle, or four.
It's in the racing where the differences really become critical. Getting around the track quickly takes a different technique in each, but getting past your competitor requires altering a driver's mindset.
“The four-wheel drives are a lot more reactive,” says Renezeder. “The decision making needs to be a little quicker, because there's more traction, so if someone makes a mistake, you can capitalize on it right away. In a two-wheel drive truck, you won't capitalize on a mistake in that turn or the next turn; it may be on a whole other lap. In the U2, everything is planned farther in advance. You think ahead because the two-wheel drive is all about momentum. You don't have the traction to react quickly to someone's mistake. You have to plan it, you have to set things up farther ahead.”
Just how you plan ahead when piloting a 4000lb., 900hp truck, no matter how many wheels you're controlling, is another matter entirely, and probably best left to the experts.