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Tire Education - Learning About Rubber

Posted in How To on April 1, 2013
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Finding the right tire for your 4x4 can be an overwhelming task. As the only part of your rig that is actually designed to touch terra firma, your wheeling machine’s tires can make or break its performance on- and off-road. Over the years tires have evolved substantially—from directional mud cleats to hybrid all-terrains, tire choices are immense for the light truck market.

Traditionally, mud-terrain and all-terrain tire categories have been the mainstay, but some of the molds from both sides seem to be edging towards middle ground. So which is the best tire for you? Well, only you can determine that, but we’re going to try and help. In this article we are digging into the features and tire technology that give one knobby an edge over the other. There may not be a one-size-fits-all answer when it comes to the perfect tire for your 4x4, but just knowing the basics can help narrow the field.

Decades ago, virtually all tires were of bias construction. A bias tire is fitted with multiple ply layers that are set at opposing angles. This crisscross pattern stretches from bead-bundle to bead-bundle, which creates a uniformed ply thickness, thus creating a thicker and more durable sidewall over a radial. While this design creates a very tough (and often heavy) tire, they do not have the on-road stability that a radial-constructed tire can offer. If we’re just hitting the trail, a bias tire is a great choice. When mixed on a daily-driven 4x4, the bias is out-matched by the smooth-rolling and stability of a radial.

The traditional all-terrain tire has changed drastically over the past decade. Some modern variants even more closely resemble mud-terrains than the standard, tightly-spaced all-terrains of old. The concept of an all-terrain is to have a tire that works well in all conditions, including rain-soaked highways, where mud-terrains sometimes falter. The tread voids in an all-terrain remain close, which allow them to roll smoother, quieter, and often last longer. While the tighter voids prevent most all-terrains from excelling in the mud, for most daily-driven 4x4s, the modern all-terrain tire works extremely well.

Dual Compound
Dual compound refers to the material makeup of the tire (i.e., polyester, nylon, Kevlar, etc.). By merging different compounds, manufacturers can create blend materials to create a sidewall construction that is different from the tread and vice versa. The goal is often to create a tire with increased strength and heat resistance so it can last longer and not hinder performance.

Circumferential Groove
These are grooves that span the circumference of the tire. A tire that is designed to excel in wet weather may have more than a tire that is tuned for dry conditions.

As we mentioned elsewhere in this issue, plies are the rubber-coated fabric and bands that comprise the tires core. More plies can equate to a stronger tire, but also make for a heavier and stiffer tire. Your rig’s weight, intended use, and performance expectations should all be considered when examining a tire’s ply-count and load range ratings. It’s doubtful you’ll need a 10-ply, load range E tire on your lightweight Jeep Wrangler, but you wouldn’t want a light-duty load range C tire on your 1-ton truck. Sometimes, it can be a tradeoff between sidewall strength and the tire’s weight. A lighter tire will be easier on drivetrain parts and fuel economy, while a heavy-duty sidewall may be the difference between a fun wheeling outing and a flat tire.

Mud-terrains can range from extreme, terrain-chucking monsters, to tame, daily-driver treads. The greater the tread spacing, the better they will shell out mud and dirt. The larger tread spacing can also give them poor road manners, especially in wet on-road conditions. Mud-terrains with extra sipings and a mild tread stagger tend to have better on-road performance over those that don’t.

Kickout Bar
A kickout bar is a common feature on most radial mud-terrains. The bars intentions are to break up and prevent mud from suctioning between the lugs. They are often placed on the edge of the tires tread and can double as a wear indicator.

Rain Groove
A rain groove is designed to channel water away and out of the tires tread. The idea is to direct the water into a groove so the rest of the tread can better grip the road and prevent hydroplaning.

Most modern passenger car and light truck tires are of radial construction. Unlike a bias-ply tire where the plies are cross-patched and even throughout the tire, radial tire bands are placed at a 90-degree angle and are different at the tread cap and sidewall. This design gives the radial a more even footprint and aids on-road handling. Since the sidewalls have less material than the caps, they are more susceptible to damage when compared with a comparable bias-ply. Ultimately, the tradeoff is street manners over brute strength. For most street-driven 4x4s, a mud-terrain radial is a nice balance of on- and off-road performance.

Rim Protector
Rubber protecting metal may seem like a strange notion, but that’s exactly what the rim protector is designed to do. A rim protector is a shelf or bulge that shadows the bead on the outside of the tire. These small guards are especially helpful when running low air pressure off-road.

Shoulder Lugs
When the tread extends onto the side of the tire, it is there for more than just looks. These shoulder lugs can often dig up traction when the face of the tire is stuffed with dirt. Since bias-ply tires run a continuous ply construction throughout, you’ll often see them with larger and longer shoulder lugs over conventional radials.

A sipe, sometimes referred to a as a kerf groove, is a small cut that is placed into a tires tread. The name sipe comes from John Sipe. Sipe was a factory worker in the 1920s who discovered that by cutting small slits into the bottoms of his shoes he wouldn’t slip as easily at work. The same principle is used in tires. The small cuts in the tires add additional biting edges that help provide better footing in wet and snowy conditions. These small grooves can also make a tremendous difference when trying to drum-up traction on icy surfaces.

Wear Bars
As your tire loses tread, wear bars or wear indicators allow you to easily measure the reduction. A tire is generally considered worn when only 2⁄32-inch of tread remains. Tires such as this Interco IROK radial shown here have steps at the foot of the lugs that work as wear bars.

Tread Depth
The distance from the top of the tread to the base groove in a tire represents tread depth. The measurement is taken at the centerline of the tire and is measured in thirty-seconds of an inch. If a tire comes new with 13⁄32 tread depth, you have 11⁄32 of usable tread.

Tread Block Angle
To increase lateral stability, tire manufacturers will angle the tread blocks across the tire. This increases side-to-side grip, but can sometimes make it harder to eject mud. Side-hilling and off-camber wheeling benefit greatly from angled tread blocks.

Tread Pattern
The arrangement of lugs on a tire is known as the tread pattern. Some companies offer asymmetrical (opposing sides are not identical) and directional designs, but tread spacing and angle play a major role in the overall effectiveness of the design. A tire’s pattern type can be as versatile as the vehicle that it is on. Most mud-terrain radials have a similar tread pattern formula, which works well for the majority of our uses. Considerations like rolling resistance, road noise, intended use, and material types all play important roles in crafting a tires final pattern.

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Tread Void
A tread void is the empty space between lugs. Mud-terrain tires are fitted with larger voids over all-terrain tires to increase the room for mud to escape between the lugs. Larger voids can equate to increased road noise, but will generally work better off-road. Greater voids can build more heat on-road, which will limit the tire’s life.

Tread Compound
The tires construction and material type is the compound. Some companies offer “sticky” or competition-only compound tires which are softer than your average radial-tire compound. Softer compounds tend to grip and hold terrain more effectively over stiffer compounds. The main drawback of a softer compound is that it heats up and wears quicker. A tires tread compound can be measured by a durometer (a device that measures the tires hardness). For the most part, the benefits of an extremely soft compound are usually noticed only in rocky and dry enjoinments.

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