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Truck Tire Tech - Anatomy Of A Tire

Tread
Tori Tellem | Writer
Posted September 1, 2006

What Makes it Roll

There was a covert operation going down at Moab this year. While most people were deep in the trails, BFGoodrich was out there taking a survey on concept tread designs for its next-generation all-terrain. The tiremaker was having people consider each pattern and rank them, then explain what they liked or hated about what they saw. If you think about it, it makes sense to draw in the public before moving forward on any tire idea. Sure, performance is crucial, but aesthetics? That's nearly as important to a tire's success.

We spend a lot of time doing comparos and shootouts in this magazine, but how does the design, material, and marketing mumbo-jumbo actually factor in to what makes a tire right for your truck and needs? Once you understand the genetic makeup and science behind its existence, you'll become a better shopper. We spoke to engineers, program managers, and developers at BFG (Gary Enterline and Kip Newton) and Pro Comp (Jedd Emans, Jeremy Jacobs, and Nick Schieltz) for behind-the-scenes action.

We'll give you only enough info to understand how it's done but not enough to make your own, because the last thing we need are the BFGs and Pro Comps of the world taking a hit out on us.

The tire-making process is essentially the same for all manufacturers: Take the tread sketches (usually in 2-D) and feed them into a computer program to create a 3-D model, which allows for easy modifying of dimensions, profile, footprint, and so on. Next would be to choose carcass construction. Does it need puncture resistance? Is a comfortable street ride important? Following the virtual tire would be a mold. And, just as with an automaker, a tire manufacturer utilizes a proving ground for testing. For example, Pro Comp has a track south of San Antonio, while BFG's is in Lawrence County, South Carolina.

The thousands of acres include varying asphalt tracks, surfaces, and off-road areas, so once they have a physical tire, they head there. They may also hit places such as Michigan or Montana for winter testing, and could take advantage of partners in the off-road business to do real-world testing (say, rockcrawling championship competitors). The type of tire-street, all-terrain, mud, rock-determines where it spends most of its evaluation time. For example, BFG's rock-ready Krawler would inevitably spend less time on the road. Then, once the prototype tire has been proven to work as designed, it would head to production and off to the tire shops.

It's easy to forget those four circles that help you float across a mud pit or crawl right over a rock are also responsible for holding up your truck. That's done via the tension in the carcass, which can also be called the casing or body. The outermost part of the tire is the tread or crown area, which transmits the forces to the ground and is what features the grooves and lugs. The sidewall usually starts at the end of the tread lugs and wraps down to the bead area.

Tires in the United States generally are constructed of two steel beads, 10 or more polyester plies, and two or more steel belts. To increase high-speed capabilities, there may also be 10 or more layers of nylon or Kevlar above the belts, restricting the belts from rising. Kevlar is used because it's super strong-but it's also pricey and that means it can make a tire more expensive. The tire's purpose (mud, street, or multipurpose) will determine which materials are put into its construction and how many layers of each will be used.

The tire's intended use will also determine the tread pattern, such as how big the grooves will be, where they are located, and whether they're straight or angled. Engineers have the challenge of not losing function for eye appeal: traction, element stability, wear-resistance, puncture and chip prevention, hydroplane repression, and manufacture-ability among the considerations. Remember those secret patterns BFG showed at Moab? When the concept tread chosen for the new all-terrain goes into production, it may not look exactly like what ranked highest in the survey. The engineers will come close, but if the grooves that screamed rugged in the survey cause the tire to shred rubber when rolling over rocks, its design would have to be tuned. But tire manufacturers get rack-appeal so they'd try not to stray too much. And they also know that making tires is all about compromises. They're actually accepting of the fact that building a tire may require some sacrifices-as in, they know that if you'll end up a hero off road, you'll probably be OK with extra noise on the street.

It's an argument in the off-road world: which is better? Die-hards say bias-ply but everyone else has their argument for why radial is the best choice. Before we give you the pros and cons for each, let's first break down the differences. Bias ply and radial both refer to carcass construction and how the materials are laid out. To understand, picture the centerline of the tire. With a radial, the carcass plies and steel cords are at 90 degrees to that centerline in a very uniform fashion running circumferentially around the tire. This makes for a durable tread in terms of wear resistance and better fuel economy, but the sidewall may be less stiff.

With a bias-ply, the plies will be at about 45 degrees to the centerline, at alternating angles in a crisscross pattern. That overlap will make them strong, but also causes them to generate a lot of heat, resulting in a tendency to flat-spot. Some radial tires do actually have a slight bias angle on at least one of the body plies, which is done for carcass protection, particularly for severe off-road use. But even though there is an angle (which may be referred to as a cross ply), it's so slight the tire is still allowed to be called a radial.

What makes a radial a better choice? Lots of sidewall flex (thanks to more radial-ply angles), it's commonly more stable (ideal for high-speed stuff like bombing down fire roads), and it performs well for mixed usage. On the downside, it can be more expensive and the sidewalls usually are less stiff (but the tread is strong). A bias-ply tire is usually cheaper, commonly has better puncture resistance because of the thicker, stiffer sidewall, and often does better in soft terrain.

Sources

BFGoodrich
Greenville, SC 29602
877-788-8899
www.bfgoodrichtires.com
Pro Comp
Compton, CA 90220
866-232-0665
www.procomptires.com
Franklin Tire & Suspension
Yuma,, AZ 85364
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