Author: Craig Perronne Photos: Craig Perronne
Unless you are buying a Ford Raptor, Jeep Rubicon or some other off-road oriented vehicle, the majority of tires from the factory floor simply aren’t up to the hard use that is commonly found in the Dirt Sports Nation. With manufacturers having to buy four tires for every vehicle sold, the overall number of tires needed can be mindboggling. This is especially true for such popular sellers like the F-150, of which Ford sold 528,349 in 2010 (or 1,447 every day!). With numbers like those, it is not surprising that OEMs can be very cost-conscious when it comes to buying more than two million tires a year just for the F-150 alone. Add to that the fact that the majority of those trucks sold will never touch dirt, and manufacturers have very little incentive to shoe their vehicles with tires that offer high puncture resistance and better off-tarmac performance. The result is that the majority of vehicles come with tires that, while decent for street use, offer very little performance in the dirt. Many of us already know this, and that is why the stock tires are one of the first things to get replaced upon acquiring a new vehicle. Even when larger tires are not needed, better ones are often swapped in place of the factory doughnuts. Of course, like with anything you are putting on your vehicle, there are a few considerations that need to be accounted for first. Let’s take a look at some of the basics of tires and some factors that need to be thought about before buying your next set of rubber. For veterans this information will be old hat, but for those looking to source their first set this can be seen as the start of what should be lots of research. For a plethora of quality, motorsports-proven tires to choose from click on the Dirt Sports tire guide here.
While often overlooked, sidewalls contain very important information such as load range ratings as well as details on construction.
Sidewall Hieroglyphics The sidewall of any tire contains a lot of markings that, at first, might just look like gibberish but are actually very important. Of course, the one most of us notice first is size. For anybody who graduated elementary school it is pretty easy to figure out what size a tire is with 37x12.50R17 listed on its sidewall. If you have trouble here, then it is time for some serious educational retooling. Besides the standard flotation measurement, the other common tire size specification is P-Metric and, while some may claim that the metric system is the work of the Devil, it is still fairly simple to explain. Using the tire size 285/70R17 as an example, the first number (285) is the width of the tire in millimeters. The next number (70) is called the aspect ratio, the height of the sidewall expressed in a percentage. Finally the last digits are the diameter of the wheel in inches. Using this formula for the example above we get a tire that is 11.22 inches wide. Multiplying this number by 70 percent we get a sidewall height of 7.85 inches. To get the total diameter of the tire we double this number and then add the wheel diameter (17 inches) for an overall size of 32.7 inches. While there are a few more steps involved than the standard flotation measurement, it is really not that complicated. While sizing is fairly basic, one of the most overlooked items on a sidewall can be the load rating. For light truck tires, the load rating once described the number of plies in the tire - back when they were made of cotton belts. A load rating of C denoted six plies with D tires having eight plies and so on. Now they describe a range of the weight the tire can handle. For smaller and lighter vehicles a load rating is not as important, but for those with one-ton trucks who plan to haul a lot of stuff (such as chase trucks) it can be a vital statistic. One important note to remember is not just to go by the alphanumeric load rating alone, but look closer at the sidewall to get the actual weight that the tire can handle and at what air pressure. Also, remember to multiply that number by the number of tires on your vehicle to get the total weight that can be handled. While it might seem trivial, big trucks like our Project Heavy Metal Dodge Diesel Ram weigh in at 7,000 lbs. and have a payload rating of almost 3,000 lbs. Loads like that can quickly overwhelm lesser-rated tires and lead to a blowout or other rapid destruction of a tire. Another item clearly marked on a tire’s sidewall is its construction. One never has to guess how many plies are in the sidewall and the tread as it is right there for all to see. Even what material the plies are made from is also listed, but one should always check on the manufacturer’s website to see more details about the construction of the tire.
Size Matters A surprising fact to some is that just because a tire is listed as a 37x12.50 doesn’t mean that is its exact size. Some tires will come in very close to their listed size while others will be off by as much as an inch. This can become important when trying to fit a tire, as one brand might fit while another will rub everywhere. Before buying any tire, one should always go to the manufacturer’s website to get its exact dimensions to avoid any headaches. Never just assume that all 37-inch tires from any brand will fit your vehicle, as there can be “big” and “small” 37s. Another sizing consideration to remember is that while going from a 35-inch to a 37-inch tire might seem like a big jump, it is really only gaining you an inch more of ground clearance. In case it is not obvious, this is because only half of the tire will sit below the centerline of the hub. While racers need every inch of clearance they can get and always look for any advantage possible, most of us are not trying to take an overall win at the Baja 1000 with our daily drivers. Jumping up in tire size can bring on a whole new set of issues that need to be tackled (re-gearing, different suspension, etc.) and one needs to decide if that extra clearance is worth it.
More aggressive tread patterns provide better traction and are quicker to shed mud than their all-terrain counterparts, but often produce more noise and wear quicker.
To Mud or Not To Mud We will be the first to admit that the more aggressive tread pattern of a mud-terrain tire almost instantly makes any vehicle look better. However, sourcing something just based on looks (like that hot girlfriend who turned out to be psycho and keyed your car) is not always a good idea. While the extra traction of a more aggressive tire in the dirt is a serious benefit, there are some drawbacks. Chief among the negatives is a lot more noise when compared to a milder tread pattern. While the open voids and more angled pattern of a mud-terrain tire might be great for shedding goo and grabbing dirt, they do help produce significantly more noise when on pavement. There are also large variances in the amount of noise generated by different brands of off-road oriented tires, with some producing just a pleasing hum while others sound more like being inside a jet fighter. Make sure to research just how much noise a particular brand of tire makes before plunking down your hard-earned cash to keep from driving yourself insane with the constant humming burned into your brain later. Another bummer is that as a tread pattern becomes more aggressive, usually wear increases, leading to a tire that lives for fewer miles. Just like road noise can vary greatly between brands of mud tires, so can the amount of life a tire has to offer. Again, make sure to do the proper research to see what the real world mileage a tire has before spending your money on it only to be disappointed later. Those who really need a mud terrain probably already know it from the amount of time they spend in the desert or on the trail, and a more aggressive tread pattern will serve them well. However, if your vehicle spends most of its time on the pavement and you drive lots of miles every year, then you might want to consider carefully what tires you are putting on it. Tires are an expensive item, and deciding which brand and type to buy shouldn’t be taken lightly or just done on price. Being realistic in your needs and actual use of your vehicle will lead to a better tire choice and a happier you in the long run.
How many plies a sidewall is made of along with the material used is also another important consideration as sidewalls take a serious beating off-road at speed or in the rocks