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Tire Dictionary - The Walking Tread

Posted in How To: Wheels Tires on April 30, 2015
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As magazine editors, we try and be somewhat accessible, (hence why we list our direct email address with our articles). This typically equates to a steady stream of reader emails, which is a good thing. One of the most common topics we’re emailed about centers around tires. Given how much a set of treads can set you back these days, we’re not surprised.

The right tire can make all the difference for both on- and off-road performance. With so many options and in-between all-terrain/mud-terrain hybrids, shopping for tires can be pretty overwhelming. To help you narrow the field, we are peeling back the layers of a light-truck tire and giving you the info you need to know to be a more informed buyer.

All-terrain vs. Mud-terrain
Years ago, we used to joke that most all-terrains were really everything but mud-terrains. Now, it’s not so black and white. We’re seeing a significant change in the all-terrain landscape. More companies are designing “tweener” tires that offer the large and staggered mud-terrain-like pattern, with the extra sipes and blocking needed for increased on-road and adverse-weather handling. For those who daily drive their wheeling machines, these middle ground rubbers are growing rapidly in popularity. Some great examples of the middle-ground tires would be the Mickey Thompson ATZ, Falken WildPeak A/T, and Nitto Exo Grappler.

With that same push of the all-terrain to a more aggressive direction, we are seeing mud-terrain radials getting plenty of refinement as well. While tread spacing and stagger is still key in a true mud tire, the addition of extra sipes, biting edges, and block alignment, is upping the on-road benefits of the modern mud-terrain radial. It should be noted that tipping the scales farther in the hardcore direction with a mud-terrain tire tends to decrease the tires life expectancy and on-road manners. We’ll always love the Interco Boggers tractor-like performance benefits off-road, but it’s not something we’d suggest for a daily driver.

All-terrain vs. Mud-terrain

Compounds
The material makeup of the tire (i.e., polyester, nylon, Kevlar, steel, and so on) can be quite complex. 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. The materials used will be printed along the sidewall of a given light-truck tire.

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

Circumferential Groove

Mmm, Plie…
Plies (not pies) are the rubber-coated fabric and bands that comprise the tires core. More plies will generally equate to a stronger tire. Your Jeep’s weight, intended use, and performance expectations should all be considered when examining a tire’s ply-count and load range ratings. 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.

I Love This Bar…
Kickout bars are used to break-up and prevent mud and debris from suctioning between the lugs. The bars are often placed on the edge of the tires tread and can double as a wear indicator. These are most common on mud-terrain tires but can be found on some all-terrains as well.

I Love This Bar…

Lip Guard
A rim protector or lip guard is a shelf or bulge that shadows the bead on the outside of the tire. These small guards work to protect the outer lip of the wheel and act as an additional debris barrier for the bead.

Rain Groove
Hydroplaning is one of our least favorite things to do in a Jeep. A tire’s rain groove is crafted to lessen that likelihood by channeling water out and away 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.

Rain Groove

Shoulder Lugs
Mickey Thompson calls them Sidebiters, we call them shoulder lugs. When tread extends past the cap of the tire and onto the sidewall, it’s known as shoulder lugs. This bonus tread will 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.

Shoulder Lugs

Sipes
A sipe, sometimes referred to as a kerf groove, is a small cut that is placed into a tires tread. The name sipe comes from John Sipe. He 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. All-terrains are going to have more sipes in general, which make them a better all-around tire.

Sipes

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 1⁄32 of an inch. If a tire comes new with 13⁄32-inch tread depth, you have 11⁄32-inch 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 block angle is also a factor in road noise.

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.

Tread Pattern

Tread Void
A tread void is the empty space between lugs. Larger voids allow more room for dirt to escape, but tend to create more road noise and less grip on the pavement. It’s typically safe to assume that the tighter the voids, the less effective it will be in the mud. For wheeling on the rocks, smaller voids can be a plus as it allows the tire to maintain a more consistent and greater contact patch. This ultimately equates to more traction.

Tread Compound
The tires construction and material type is the compound. Some companies offer “sticky” or competition-only compound tires that 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. Many soft-compound tires are also not DOT compliant. A tire’s tread compound can be measured by a durometer (a device that measures the tires hardness).

Radial vs. Bias
While not as common these days, bias-ply tires used to be the norm. Bias-ply tires are comprised of multiple ply layers, which are set at opposing angles. The crisscross pattern stretches from bead-bundle to bead-bundle to create a uniformed ply thickness. Ultimately, this construction is believed to create a thicker and more puncture-resistant sidewall. The two main drawbacks of the bias tire are that they typically weigh more and lack the on-road stability compared to a radial.

Where a bias-ply tire has cross-patched plies throughout, a radial’s bands are placed at a 90-degree angle. They are also different at the tread cap and sidewall. A radials construction is meant to provide a more even footprint and stability. Sure, the radials have less material at the sidewall when compared to a bias-ply tire, but the advanced construction, materials used, and high load-range ratings, have made the modern off-road radial a real contender in strength. For a daily driven wheeler, the radial makes the most sense, hands down. If you have an off-road only Jeep, a bias-ply tire is definitely worth consideration.

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.

Wear Bars

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