Choosing Tires For Your 4x4 - Beefy Tire TechPosted in How To: Wheels Tires on August 1, 2009 Comment (0)
Tires are round and black-what else do you really need to know? That depends on what you want from your tires. If your only concern is to roll down the road, you're pretty much done. But we're betting you'd like to have more traction in the loose stuff, perhaps some sidewall protection from trail debris, and some insight into why there are hundreds of supposed off-road tires. Most importantly, you'd probably like some help figuring out which tire is right for you and the way you use your vehicle.
Tires are often the first thing to get changed on a 4x4. That's because tires can completely change the performance of your vehicle, and the appearance too. Larger tires give your ride more ground clearance for better four-wheeling, and the tread and construction of the tire can make a night-and-day difference in motoring through soft sand, driving through sloppy mud and traction on wet pavement. The next few pages will act as a primer on tire technology and selection. Next month, we'll address wheels, since they are often upgraded at the same time.
This is what most people judge off-road tires by, and rightfully so. A super-aggressive tread pattern delivers the promise that this tire will fling mud and sand, and grab rocks like a skilled rock-climber. It's also one of the key visuals that sets your 4x4 apart from a stocker in the parking lot. To give you a quick comparative look at some of the most common treads on the market today, we have grouped 10 treads, side by side. (See "Footprints" on page 62 for these images and a bit of information about each of the tires.)
For our purposes, there are five basic groups of tread design: Street, all-terrain, extreme all-terrain, mud-terrain and rockcrawler. You'll sometimes hear about mud and snow tires (or M&S), but that just means it meets the Rubber Manufacturers Association guideline for this designation. And while these guidelines might have meaning for snow and the type of mud that oozes across the road once in awhile, it's not a good measurement of what we're looking for in a mud-terrain.
Street tread is designed for maximum traction on pavement and good tread life, period. These are the tires you might choose for your wife's Tahoe, but they don't offer advantages for any off-pavement use. Because of that, we have not included any of them in this article.
All-terrain tires cover a broad range of tread types, and are a great compromise for general-purpose use. These perform well on pavement and deliver moderate performance off-road as well. The tread is generally an interlocking design with more voids than a street tread. All-terrain tires also almost always feature siping, or very small grooves cut into each tread block, for better grip on smooth surfaces and ice. This type of 4x4 tire offers good tread life, a quiet ride and very good on-road handling characteristics. These are a great choice for a vehicle that you use primarily on road, but want a bit more capability for occasional use off-road. The BFGoodrich All-Terrain T/A KO is the iconic tire in this segment, being introduced in 1976 and enjoying a healthy market share over its life. Other current examples include the Goodyear Wrangler SilentArmor, General Grabber AT2 and Pro Comp Radial All-Terrain.
There is also a new category of hybrid tires-offering on-road manners and handling closer to an all-terrain tire and providing more grip than a typical all-terrain with more aggressive side lugs and larger voids between these side lugs. Examples of these tires are the Mickey Thompson Baja ATZ Radial, Goodyear Wrangler DuraTrac, and Pro Comp Xtreme All Terrain Radial. These tires are perfect when you really want more off-pavement performance than a traditional all-terrain can offer, but you want as much on-road traction and minimal road noise. They also look cooler than an all-terrain tire. This might be the perfect choice for a 4x4 tow vehicle.
Mud-terrain tires have been the standard tire for off-road performance for decades. And they still provide the best all-around performance off-pavement with larger lugs and more space between tread blocks to grab a lot of terrain. The larger voids let the tires clean out easily with a little bit of wheel spin. Generally, they don't perform as well on-road compared to a street tread or all-terrain, and the tread life is isn't as long, but you're running these tires for what they do for you in the dirty stuff. Examples of tires with this tread design are the BFGoodrich Mud-Terrain T/AKM2, Goodyear Wrangler MT/R with Kevlar, Mickey Thompson Baja MTZ Radial, Toyo Open Country MT and Pro Comp Xtreme Mud Terrain Radial.
Rockcrawling tires have evolved in less than 10 years as the rockcrawling sport has grown. The BFGoodrich Krawler T/AKX was the first tire on the market for this group of extreme wheelers who only cared about traction for rock crawling. So the attributes of this segment are massive lugs with extreme spacing, puncture-resistant sidewalls, and very soft rubber compound. The Krawler continues to focus on rockcrawling performance, while the Mickey Thompson Baja Claw Radial and Pro Comp Xterrain Radial also have aggressive tread patterns, but offer good performance in mud and on pavement as well.
One area of significant advances in tire composition for the 4x4 market have been in the strength and protection of the sidewall against puncture from rocks, tree roots and other trail debris. Goodyear recently introduced the Wrangler MT/R with Kevlar. This tire uses DuPont Kevlar in the sidewall to provide at least 35 percent more puncture resistance compared to other Goodyear tires. (See our review on page 66 for more.) BFGoodrich uses its TriGard technology-a combination of aggressive sidewall lugs, cut- and chip-resistant sidewall compounds, and stronger sidewall cords-in the new Mud-Terrain T/AKM2 and Krawler T/AKX tires. Pro Comp and Mickey Thompson both use three-ply sidewalls to provide protection.
Another category of tire construction is rubber compound, or the chemical composition of the actual rubber. Softer-compound rubber makes tires more flexible and gives them better grip on pavement and on rocks. But softer compounds also wear at a greater rate, giving you fewer miles before it's time for a new set. It's a trade off, a lot like horsepower and fuel economy. If you opt for a truck that gets 25 mpg, you're probably going to spend a lot of time waiting to get to 60 mph each time you get on the freeway. Choose the 400hp engine, and you'll have to live with 10mpg fuel economy. But there are plenty of options in between to create a compromise that's right for you.
Every once in a while, you'll hear someone waxing on passionately about how good bias-ply tires are for off-road driving. Usually these guys have a permanent three-day beard, have never actually bought new tires (ever), and they prefer not to be concerned with modern advances like phones. (Hoo-boy, here comes the hate mail.-Ed.) But since people talk about them, here's a basic explanation of the two primary types of tire construction: Bias-ply and radial.
Bias-ply is the older way that tires were manufactured, with layers of cords (usually made of nylon) applied diagonally to the centerline of the tread, in alternating angles. A strong bias-ply tire requires more layers, but this holds more heat, adds weight and creates a stiffer tire. This construction does provide very good sidewall puncture resistance when six or so layers of cords are used in the construction. Another reason that bias-ply is favored with some four-wheelers is that the original 4x4 tires with aggressive tread patterns had this construction. Bias-ply tires used today are usually very specific in application, and are generally reserved for utility trailers and agricultural use. There are some extremely large sizes where bias-ply construction is the only type available, and if you are building a mega-tired monster rig for an event such as Top Truck Challenge, bias-plies may be your only option.
A radial tire is composed of steel cable belts, applied bead-to-bead (i.e., at a 90-degree angle to the tread face) and coated with rubber. To make a stronger radial tire, larger steel cables can be used. The overall composition of a radial tire manages heat much better, creates a more flexible sidewall for better ride characteristics and has a more stable tread patch.
Because of the advantages of construction, radial tires have won out in the mass market. That's not bad for the 4x4 market, as a radial offers very good sidewall flex with stable tread surfacing, better fuel economy, longer tire life and a good ride. Advances in off-road-specific technology such as additional sidewall protection and aggressive tread patterns make radial tires a very good solution for almost all 4x4 applications.
Which tire is right for you depends on a few key factors: what's the most important use of your 4x4 that you want to optimize tire performance for, if looks are important and desired size. Any one of these three can be the dominant factor in your decision, but notice we didn't say how you will use your vehicle. How you want to use it is much more important in making a tire decision you'll be happy with. If you want the best mud performance, even though you'll only go mudding once or twice a year, it would be much more practical to go with an all-terrain tire, but you're probably going to be happiest with a mud-terrain tire. Be honest with yourself and closely evaluate the compromises of each decision. Tires can be the best purchase you can make for your 4x4.
Reading a Tire
Like so many things in the automotive world, reading tire size can seem like a secret code. Here's the decoder ring so you can be a cool kid in the club
Tire size can be displayed in two forms. The first is a traditional off-road size designation and is pretty straightforward. In this form, a 33x12.50R16.5 tire is 33 inches in diameter, has a 12.50-inch tread width and fits on a 16.5-inch wheel. The "R" designates it as a radial tire.
If you thought metrics would go away when you left school, guess again. The more common tire size designation is a metric measurement. In this photo, 315/70R17 is shown and is broken down as follows:
315 = overall width of the tire in millimeters
70 = is the aspect ratio, or the approximate sidewall height of the tire as a percentage of the tire width (70% of 245mm tire width = 171.5mm sidewall height)
R = radial
17 = wheel diameter in inches
Other information you will see near or embedded in the size designation is a two- or three-digit load rating. This number corresponds to the weight capacity of the tire. Usually, you don't need to look up the weight capacity in a chart, however, because it is found elsewhere on the tire with the recommended tire pressure.