With the amount of time the Lucas Oil Off Road Racing Series Pro 2 and Pro 4 Unlimited trucks spend in the air, sliding in corners or just generally spinning their wheels, it may seem like tires are an afterthought. After all, it only matters how the rubber meets the road when the rubber meets the road, and it doesn't seem to happen all that often with these racing trucks.
But it takes some oomph to get them shooting out of the corners and over the jumps, and the tires, just as in every form of racing, are the point of transfer from 900hp engine to the dirt. And because these trucks are sliding in the corners, spinning their wheels furiously as they fight for traction and eventually coming down to earth after launch over a tabletop, the tires must be able to withstand a fair amount of abuse.
Short course off-road races are short in duration as well – usually less than 30 minutes and somewhere around 20 miles – so the tires don't have to be long-lasting, just tough. And they are tough in different ways than their desert racing counterparts. Desert tires need tough, thick sidewalls to fend off sharp rocks and wayward tree branches. Short course tires don't, so they can be lighter.
The tires used on the Pro trucks are a different breed than any other tire, competition or otherwise. They are built uniquely for the sport and have characteristics not found in other off road tires – even if the competition tire is based on street-legal, Department of Transportation (DOT)-approved rubber or vice versa.
“A lot of technology that goes into an [original equipment] tire comes from what we learn here in racing – compounds, sidewall strength, durability, it all comes from race development,” explains Victor Angon, off-road motorsports coordinator for BFGoodrich Tires. “But the race tires, unlike your regular street tires, come in several different compounds. We run an inner liner, which is like an inner tube, that actually bolts onto the tire and makes it a little bit stronger and if they get a flat, they can continue to run.”
The different compounds are key – the Lucas Oil Off Road Racing Series may just run on dirt, but the dirt at Las Vegas Motor Speedway is different from the dirt at Speedworld Off Road Park is different from the dirt at Miller Motorsports Park is different from the dirt at Glen Helen…. And the dirt changes drastically with conditions. The tires for the Pro 2 and Pro 4 trucks are typically pretty soft. And usually Pro 4 can run a softer compound than the Pro 2 trucks because they're using all four wheels to get power to the ground and spinning the tires less.
Walking around the paddock, one might notice that although two tires may have the same manufacturer on the sidewall, they may look quite different. That's because the tires that a company brings to the track may be very different from what ends up on the truck for the races. Short course off-road tires have a minimum of tread; the teams can then groove them as they like.
“Our race tire is based on our regular production tire. The only changes we really make is in our tread compounds,” explains Rudy Consalacion, motorsports manager for Kumho Tires. “We remove some of the grooving in the molds so we get more of a blank canvas to work with, Depending on what the driver wants – if he wants more side bite or more forward bite, we can adjust the grooving to their desire or depending on track conditions – if it's dry, starting to blue groove, or if it's loamy or muddy.”
The tires are grooved different ways to achieve different objectives, says Dana Zamalloa, PR and Communications manager for General Tire.
“When you groove a tire, you're looking at a couple of different things. You have to meet the terrain – the races are in different locations with different dirt. In some races, you need a little bit more grip in cornering. Sometimes, we'll do a variety of things with the voids in the blocks. Our tire is a little harder, so they've been putting smaller grooves within the blocks, which makes the tires a little bit softer and more pliable. A harder tire can withstand more abuse, but there are places you want it to be softer. So putting multiple sipes in the blocks allows for the tire to be a little bit softer. When they start opening up the voids, it allows them to get a little bit more grip.”
Grooves around the circumference of the tire typically give the tire more side bite, useful for cornering. Grooves perpendicular to the direction of travel give more bite in acceleration and braking. Often, a team or driver may want to modify the tire in both ways.
“Sometimes, on the inside, we'll do more lateral [grooves] for forward bite and [circumferential grooves] on the outside of the tire for side bite, for when they're leaning on the outside edge,” says Angon. “It's a compromise. A lot of these guys like to throw the vehicle into the corner, then try to square up on it.”
With different available compounds and the ability to change the performance of the tires with hand grooving, the Pro 4 and Pro 2 competitors have a lot of options. The choices for the other classes – Pro Lite Unlimited and the buggies – are much more limited. Those classes must run on DOT-approved, street-legal rubber. And tire choice can be crucial.
“You want a versatile tire because the track conditions can change,” says Yokohama Tire's Paul Algarin. “It can be very soft and loamy or even muddy, so you want a deep tread. Mud terrains are always a favorite in that situation. But as the track wears in and later on in the race it starts to blue groove and get a hard surface, then you want more rubber on your tires. So finding that balance is the key. Softer compounds help when it gets to be a harder surface.”
The changing conditions in short course off road racing make tire choice a difficult decision, and the tire a driver wants at the beginning of the race and the tire he wants at the end are often two different things. It's a rare – and often victorious – thing when the tire that works at the green is working as well at the checker.