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Mud Tires - What Makes Them Work

Posted in How To on June 1, 2013
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We talk a lot about tires, not only in this tire issue, but also amongst ourselves and with people who actually work for tire companies. We are constantly asking why this groove went there, what made them pick this kind of tread block, how a particular compound was arrived at, and so forth. While we don’t get paid to make tires, talking to the people who do from so many tire companies gives us a good idea of how a tire goes together and just enough tire insider’s vocabulary to avoid sounding like complete idiots.

So when it comes to what makes a mud tire a mud tire, we all know big blocks and lots of voids are key. If a mud tire can’t kick mud out, what good is it? Years ago, that was all tires were—huge blocky treads with miles of space between them. What we don’t see too much of in the mud tires of yesteryear are siping, irregularly shaped lugs, space-age materials, and more of the trickery that has showed up in today’s mud tires. Today, most tire design and testing is done on computers, which has brought us some awesome designs. But what is going on in the heads of the guys running the computers? How do they come up with some of these ideas? What does their tire do better than the next guy’s? Well, to get to the bottom of it, we harassed some guys inside Cooper Tire, Mickey Thompson Tires, and Dick Cepek to get the scoop on what goes on before the tire gets to your Jeep.

Dick Cepek
We sat down with Ben Anderson, the Tire Segment Manager for Dick Cepek tires and picked his brain. He tells us that when Cepek engineers sit down to design a new tire they look at what their intended customer base might want. Cepek is aimed at outdoorsmen, fishermen, hunters, campers and the like. And to that end, the company has two mud tires, the Mud Country and the Crusher. While both tires are built on the same three-ply carcass and use the same rubber compound the treads are wildly dissimilar.

Note the shuffled tread design and the circumferential center groove (arrow) of the Dick Cepek Mud Country tire.

The Mud Country was designed to have good lug stability with a non-consistent tread with many biting edges to better grab dirt, mud, and rocks and keep you going forward. At the same time, the non-symmetrical tread (as you look across the tire from inside to outside) offers wide voids at the shoulders to kick mud out with more tightly-packed tread in the middle for better road manners. The shuffled tread (looks like a fanned-out deck of cards) provides more biting edges while making the lugs squirm less. The big center groove helps with traction in wet conditions.

The Crusher, on the other hand was built for the guy who has a truck or Jeep that might never see asphalt or for the guy who just doesn’t care how un-car-like a tire is on-road. The bold bones and skulls design was decided on because there was nothing like it on the market and the company wanted to make a statement. The bigger lugs scoop and chuck like no one’s business. The smaller bones between lugs are actually functional helping to break the mud’s suction.

The bold skulls and bones of the Dick Cepek Crusher design also works very well in both sand and mud.

Cooper Tire
We spent a bunch of time on the phone with Mike Stoltz, who is the Light Truck Product Segment Manager, and Jim Fleckner, who is the Product Segment Analyst for Cooper Tire, to find out how the company approaches new tire design.

When Cooper builds a new tire, it talks to their dealers, who in turn speak with customers about what the customer wants. For example, do they want an existing tire to do better, or is there some kind of tire design that Cooper just isn’t making, but the customer wants to see? From there, they figure out what the intended use of the tire is. Right now, Cooper doesn’t have a 100-percent mud-enthusiast tire. The company figures that all their tires will be used on-road to some degree. To that end, the most aggressive Discoverer STT was built to see 75 percent off-road usage and 25 percent on-road usage, whereas the Discoverer S/T MAXX was built for heavier trucks and vehicles that see lots of off-road usage to the tune of about 60 percent off-road and 40 percent on-road.

A shot of the tread of the S/T MAXX shows the 4-5 rib tread center block that helps life of the tire and keeps the noise down on-road.

Once the company figures out the intended use of the tire, it goes to the product design computer guys and might make up to 12 sketches. The sketches can be tested in the computer for things like tread squirm, noise, contact patch area, and more. Once the product team has some sketches it likes, it sits down with the technical team and brainstorms about what can be tweaked. All that before ever actually making a tire you could touch. From there, four to six 3D models are worked up and more testing happens. Once the company finds the design that works the best, then test tires will be built; sometimes as many as three different designs are tried. Usually by this point it is only one test tire that’s built and tested extensively, first at Cooper’s state-of-the-art test facility, and then out in the real world before it is built for the end user.

Both the STT and the S/T MAXX feature the same three-ply Armor Tek construction but slightly different rubber compounds. There are two things that make the Armor Tek unique. The first is that the third ply isn’t just in the sidewall. It runs from the bead all the way up the sidewall, across the tread, and back down to the other bead again. The other unique feature is that it is laid in there at a different angle from the other two plies to increase damage resistance. The S/T MAXX features less grooves running straight across the tread which helps with tire life in nasty conditions. A typical Cooper mud tire features a proprietary anti-chunking rubber compound that isn’t found in the company’s all-terrains.

Mickey Thompson
Mickey Thompson Tires has noticed that today’s tire buyer is more savvy than was the consumer of yesterday, and this has driven the company to make more specific treads to meet the demands of today’s consumer. Where it used to be OK to just have an all-terrain and a mud-terrain tire, today’s buyer wants more out of their tires—that has resulted in the Mickey Thompson MTZ as well as the Baja Claw TTC.

Mickey Thompson MTZ for your more dual-purpose four wheel drive vehicle.

Like other companies today, Mickey Thompson relies heavily on computer-generated design and can sometimes go through up to 20 renderings before settling on a tread to take forward into real-world testing. After the computer-generated testing, Mickey Thompson relies on real world testing to see how tires will actually do in various conditions. The MTZ was born because customers wanted a good mud tire that had a nice on-road ride and was non-directional so that it could be rotated. It was intended to be mostly an off-road tire which you can see in the three-ply construction and large voids but one that could be driven on-road as well which can be seen in the interlocking tread blocks and siping for wet and snow traction.

The Baja Claw TTC, on the other hand, came along as the original Baja Claw was getting somewhat long in the tooth and needed a freshening up. The trick then became to make the Claw work better while not screwing up what was already there. Both the new and old bias-ply Claws feature four-ply construction, but the new radial Claw has a three-ply sidewall where the old one was only two-ply. Other things that the company improved upon was to de couple the large tread blocks so that the tire was better able to “grab” rocks than the old Claw was. But, put too many grooves in there and then the tire doesn’t perform as well in the mud. So the solution was to build a ramp of sorts so that the front face of the lug still was a huge solid wall for moving mud, but the rear face wasn’t and overall it would flex better at low tire pressure.

The arrow is pointing to a decoupling groove in the tread of the Baja Claw TTC. Note how it is ramped from the front of the tread to the rear.

In addition, lug angles were changed for better self-cleaning. A lot of attention was also paid to the sidewalls with a large increase of sidewall traction over the previous generation. Remember the first year where a lot of the Top Truck Challenge competitors were rolling on 54-inch Baja Claw TTC? That was how Mickey Thompson got its real-world testing done.


Dick Cepek Tires & Wheels
Stow, OH 44224
Cooper Tire And Rubber Company
Findlay, OH 45840

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