Mud-terrain tires are characterized by large lugs with large voids between the lugs. These features offer grip through mud and over rocky terrain, plus the ability to jettison the mud to prevent buildup and loss of traction.
One disadvantage to this type of tread (with a high void-to-rubber ratio) is the noise it makes while being driven on the highway.
"Mud-terrain tires need traction off-road, and customers know they have to make concessions about increased road noise and different wear characteristics," says Thom Peebles, brand marketing director for Michelin North America Inc.'s BFGoodrich tires.
Due to the tread voids, there's also less rubber on the road. This ultimately affects wear. Aggressive treads tend to wear out faster than tires used for strictly on-road purposes.
"Tire companies try to minimize the tradeoffs," says Peebles. "The ultimate mud-terrain tire will have traction off-road and still be quiet on the street."
All mud not created equal
Traction is the main attraction with mud-terrain tires. Although a good portion of them are used as sturdy tires in the commercial field, they are often purchased for their off-road characteristics.
True to their name, these "mud-terrain" tires need to be able to maneuver through various types of mud (such as Georgia clay-laden goo and Louisiana slippery stuff), through sand and snow and over rocks.
Voids in the tread give the tire the rock gripping ability for those folks who like to travel or race over rocky terrain.
"The mud-terrain market is an extremely aggressive and limited market with a cult following of 'rough-cut' guys and gals," says David Guidry, vice president of Interco Tire Corp. "The average person is looking for a tire that is pleasant on-road and decent off-road. Usually the tire that is highway-friendly will not be good off-road. We have to match the two desires to appeal to the broadest market.
"Everyone has a different opinion on what makes a great mud-terrain tire. But it's like my dad says, 'If everyone liked brunettes, there wouldn't be enough to go around!'"
The mud-terrain tire tread also must be self-cleaning at low speeds, says Guidry. If you needed to go full-throttle to clean the tread, it would be abusive to the vehicle.
"A mud-terrain tire must have really good self-cleaning capabilities," says Art Michalik, director of marketing communications for Yokohama Tire Corp. He explains that tires with voids might not be self-cleaning, so they need a clean biting edge.
"When you look at normal road surfaces -- asphalt and concrete, that is -- the co-efficient of friction is narrow compared with mud and sand and other off-road surfaces. The tire must be versatile."
Peebles says the market has gone radial because the tires can go further afield than the old bias tires and still have acceptable ride and wear.
Also, today's mud-terrain tires need to perform in an "aired-down" situation, where customers take air out of the tires for additional traction. This is just another consideration for tiremakers, which usually concentrate on tires being run at OEM air pressure recommendations. Thus, they enhance the shoulders and sidewalls to be able to withstand aired-down situations.
Durability is another big issue. These tires usually feature three-ply sidewalls to withstand abuse. If the tires are used in a commercial work setting, tire wear is another consideration.
There have been innovations recently in the engineering of mud-terrain tires.
* Yokohama Tire Corp.'s Geolander M/T+ has new larger shoulder buttresses with protectors that enhance performance, durability and visual impact. Larger scoops from the shoulder blocks help the tread edges release mud and dirt. Every second shoulder lug is taper cut, and the protruding blocks provide a stronger side bite.
A groove has been added within the blocks perpendicular to the directional pattern to improve traction. A double-step center groove has self-cleaning capabilities and enhances water drainage.
The tires' new tread compounding enhances wear resistance to lengthen tire life.
* Toyo Tires U.S.A. Corp.'s Open Country M/T has a hook-shaped "attack" tread that ensures a solid grip in sand, gravel and on steep rock, the company says.
Plus, the silhouette of the tread wraps onto the sidewall for extra grip, whether on extreme angles or on low traction surfaces. The tire's bruise and abrasion resistant sidewall compound helps protect both the tire and rim from damage as well as cuts.
* Goodyear Tire & Rubber Co.'s Goodyear MT/R is manufactured using Durawall technology. It features the use of three sidewall plies and a silica compound for increased puncture resistance around rocks, the company says.
The company's Dunlop Radial Mud Rovers offer an aggressive tread with a wide, open shoulder design for maximum forward and side grip. Alternating shoulder lug scallops increase lateral stability, the company notes. The Mud Rover has six full plies under the tread for tread block stability and durability, and a high ply turn-up for responsive handling and increased lower sidewall durability.
* Michelin North America Inc.'s BFGoodrich Mud-Terrain T/A KM (for Key Feature Mud) is engineered with the company's TriGard sidewall construction technology, which features three heavy-duty plies. The tire's DiggerLugz design gives it the ability to power through the most difficult terrain, say company officials.
* Pro Comp Tires' Mud Terrain has a twin rib center traction zone with interlocking, open, aggressive twin high void lugs and a 90-degree checked siping pattern for wet weather traction and bite on rocks and hard surfaces.
Its shoulder corner lugs have deep traction bars to maximize the biting edge for increased traction in rocks and mud. The tire's Dualguard polyester body plies are puncture resistant and flexible - without heat buildup -- when lower off-road air pressure is used, the company says.
The Mud Terrain also has two layers of opposed angle steel belting spanning the tread area for maximum puncture resistance. The opposed angle steel allows the tread to flex under lower air pressure to maximize traction in rock, mud and sand.
* Maxxis International Inc.'s' MT-754 Buckshot Mudder has an extremely aggressive tread pattern as well as a rugged sidewall in order to handle the most extreme terrain, the company says. The Buckshot Mudder has double steel-belted radial construction for long-lasting wear and uniformity, and a jointless, spiral-wrapped full nylon cap for added strength and stability. An extra strong, durable casing helps resist punctures and abrasions. Its premium rubber compound and tread siping delivers maximum control in various weather conditions.
Maxxis' Bighorn radial has staggered shoulder lugs for added traction in uneven terrain and deep tread blocks for self-cleaning capabilities. It also offers optimum handling capabilities on all hard terrains, the company says.
* Mickey Thompson Performance Tires & Wheels' Baja Radial MTZ has variable sized, wide-void tread lugs for quick self-cleaning capabilities. The company's Sidebiters offer an extreme look and aggressive off-road, all-weather traction, the company says.
* Bridgestone Firestone North American Tire LLC's Bridgestone Dueler M/T is constructed with the company's UNI-T technology to conquer any type of terrain. It has a rounder overall tire shape that provides balance for wet or dry handling, and has extra large and deep lugs for traction in extreme conditions. The company says its Firestone Destination M/T with UNI-T technology offers optimum wet braking and handling. It incorporates the company's DMR Max Traction Light Truck Tire Technologies and has deep skid lugs and three body ply construction.
Racing is big business
As Yokohama's Michalik says, "Mud-terrain tire customers are enthusiasts who know about tires as much as Porsche enthusiasts know about Porsches."
One reason for this is the tire companies' involvement in racing events.
Mud-terrain tires are considered by tire companies to be "high performance" tires since they are often used in races such as Championship Off Road Racing (CORR) and SCORE International Off-Road Racing events.
Maxxis is involved in racing in a big way. Some of its activities include offering prize money for the Pro-Lite class of CORR, sponsoring off-road race events and providing technical support with an on-site rig. It also awards race winners with its Buckshot Mudder or Maxxis Bighorn mud-terrain tires.
Mud and dirt racing is becoming huge, says Interco's Guidry. "It's a good family environment. It's a good value for parents with children. They can spend a day tailgating, and the cost of a mud race is usually about $5 for adults. It's good, cheap entertainment."
Industry experts say that while some 60% to 70% of the tires are probably used in traditional applications, 10% are used in racing.
Michelin is addressing the market with the new limited-edition version of its BFGoodrich Mud-Terrain T/A KM that fits 22-inch wheels and features a concept tread design. The new tire comes in size LT335/55R22.
"This is the first time we have ever launched a limited-edition tire, and it's also the first ever BFGoodrich off-road tire designed to fit 22-inch wheels," says Gary Enterline, BFGoodrich light truck tire category manager. "The new size and tread design is aimed at consumers who are customizing their trucks and SUVs and want an off-road look on a larger wheel diameter."
The limited-edition tire is designed to provide optimum off-road traction plus style for use on the street. It is based on a prototype design that Michelin initially showcased at the recent Specialty Equipment Market Association Show on a custom Fox Racing SMA HUMMER H2 SUT.
The design of the tire is based on the company's Krawler T/A KX tire, which has won more rock crawling championships than all of its competition combined, the company says.
"First of all, you don't fix what isn't broken," says Peebles. "We're addressing the trend for bigger rim diameters. Form follows function.
Michelin collected input from race teams and consumers to come up with the 22-inch tire. "We are working with enthusiasts because we're making them for enthusiasts."
Michelin will gauge receptivity of the 22-inch tire for the next six to 12 months to determine whether or not it will expand the line. "We already know it has a good heritage," he says.
Toyo Tires has a 24-inch size for its Open Country M/T mud-terrain tire. It is available in a 37X13.50R24 size.
"Last year, Toyo established a whole new market segment with the introduction of our 40-inch Open Country M/T to fit 22-inch diameter wheels," says Toyo's Kevin Lakkis, product manager for light truck tires. "This new size takes tire technology even further and creates truly unique options for custom pickups and SUVs."
The Open Country M/T uses Toyo's DSOCII computer technology, which results in optimum handling both on the highway and off the road.