How To Choose Tires and Wheels


  • How To Choose Tires and Wheels

    How To Choose Tires and Wheels

    Previous generation Miatas came with 14-inch wheels and a 185/60R14 tire. This '99 has 15x6-inch wheels and 195/50R15s, a plus one upgrade. | March 18, 2010

4 Photos

We know you've heard it before, but it's critical enough to bear repeating. It's also a bit daunting, too, that the tires on a vehicle are the one single link to the road surface. Think about that for a moment. You can have the most powerful engine, the most sophisticated transmission, the most elaborate super-trick suspension, and every other automotive widget known to mankind, but it all ain't worth a tinker's damn if the tires (and wheels) are subpar. In a way, it's really a bit strange but that's just how the operation of the automobile is.

Luckily, after examining the facts in the above-noted fashion, you can rest assured that tire technology is at an all-time high and it keeps getting better. In fact, it's actually quite amazing that while crummy tires can hurt a great car, great tires can do wonders for a less-than-fantastic car. In other words, there are some instances where tire technology is way beyond many of the cars on the road.

The technology that makes wheels and tires as good as they are is also what can make the subject quite intimidating. Our purpose here is to try and put a finer point on some of the basics of wheels and tires, and how to select them, too. Think of it as a wheel-and-tire primer that will provide you with some ground-floor facts when it comes time to make a replacement tire purchase or a wheel-and-tire upgrade.

For starters, there's tons of information on the sidewall of any tire and we cover that thoroughly in Sidewall Graffiti. There you'll find the full scoop on exactly what all the numbers mean.

If you've bought a vehicle new and come to the point where you need to replace the tires, there are several ways to go. Of course the easy way is get the exact size and make that came on the vehicle when it was new. Beyond that, you might consider going to a better quality tire or one that improves dry and/or wet handling that's still the same size as the OE tire. The next step would be to switch to a different wheel and the reasons for doing that are numerous. Some people merely want a different look for the wheel while using the same tires that came on the original wheels. While this might be OK if you want to make an appearance change right away, we think it's better to wait until you need new tires anyway, then upgrade to a larger diameter wheel and tire all at once.

Known as the plus sizing concept, this basically means that if you have a 15-inch wheel, plus one would be a 16-inch wheel and plus two would be a 17-inch wheel. But before we get further into wheels, we want to shed some light on what you should know when walking into a tire store to buy tires for your existing wheels. And, of course, this info also applies when you're doing a wheel upgrade, as well.

Choosing the tire that's right for you involves numerous considerations. But to make the process less scary, keep these two simple guidelines in mind when considering tires. First, know your expected needs and driving uses. This consideration is important to overall driving enjoyment and a well-run tire shop will help you determine your tire needs before you lay down any green. But be sure that you and the salesperson communicate accurately as to your true requirements. Second, find a source or store that you trust enough to recommend the type of tire that fits your needs. Remember, the salespeople don't know your needs, you have to tell them. If they're good, they'll ask you the right questions to come up with the right tire. For example, they'll know to factor in tread life, ride and handling, and driving conditions to help you determine which of these parameters are most important to you.

You might be wondering what some of the questions could be. Here's a list of what you should think about before entering a tire store.

  1. Tread life considerations: What's your idea of how long a set of tires should last? Keep in mind that in some instances, a tire's wear rating is done through manufacturer testing and may not be the most accurate representation of a tire's true life expectancy. One way to get a handle on a tire's projected life expectancy (besides what they're warranted for, say, 40,000 miles for example) is to look at part of the UTQG (Uniform Tire Quality Grading) rating. The U.S. Department of Transportation requires each manufacturer to grade its tires under the UTQG labeling system and establish ratings for tread wear, traction and temperature resistance. These tests are conducted independently by each manufacturer following government guidelines to assign values that represent a comparison between the tested tire and a control tire. While traction and temperature resistance ratings are specific performance levels, the tread wear ratings are assigned by the manufacturers following field testing and are most accurate when comparing tires of the same brand. Tread wear receives a comparative rating based on wear rate of the tire in field testing following a government specified course. For example, a tire grade of 150 wears 50 percent longer than a tire graded 100. Actual performance of the tire can vary significantly depending on conditions, but the tire's UTQG tread life number can help you get in the ballpark as to how long a tire will really last.
  2. Wet weather requirements: Most of us live in a climate where inclement weather is a factor at least part of the time. Clearly if you live in, say, Washington or Oregon, you'll want to look more closely at a capable wet-weather tire than if you're in Arizona or Nevada. For those of you in Snow Belt states, some kind of four-season type of tire will be the minimum you should consider if not an all-out snow tire for the winter that you swap for standard tires in the milder months.
  3. Speed rating: Even in the plains and Western states like South Dakota, Nebraska, Idaho, Montana, New Mexico, Colorado, Wyoming, Utah, and Nevada where the rural interstate speed limit is 75 mph, how often do you think you're going to need a tire that's speed rated for anything over 150 mph? Be honest and knock down your required speed rating to, say, and H-speed rated tire that's still good for 130 mph. You'll pay less and likely not notice the difference in the real world. For reference, the most common speed ratings you'll come across on the majority of tires are shown in the chart below. Speed ratings signify the safe top speed of a tire under ideal conditions. For just about any street car, a V-rated tire will be more than adequate, unless the car will actually go faster than 150 mph. Usually, most ultra-high performance handling tires have a speed rating of at least V, so while you might want the ultimate handling of that type of tire, be aware that part of what you're paying for (the speed rating) is something you'll never use. For those who want tires that make a car really stick in the twisties, it ends up that many get the speed rating anyway, even though they don't need it. That's not a bad thing, but also be aware that tires with higher speed ratings are usually made from a softer rubber compound and generally will have shorter UTQG tread life ratings and, furthermore, will not actually last as long in the real world.
  4. Q= 99 mph S= 112 mph T= 118 mph U= 124 mph H= 130 mph V= up to 149 mph Z= 149 mph and above W= 168 mph Y= 186 mph

  5. Ride Quality: A low-profile tire such as a 50 or a 40-series looks great, but can be harsh over bumps or potholes when compared to a 55 or 60. In general, a lower profile tire also exposes the wheel to damage more easily. Lower profile tires also have stiffer sidewalls, which improves handling but increases rides harshness. It's all about compromise and there's no such thing as a free lunch.
  6. Noise: Some tread designs are noisier than others and it varies significantly between tire brands and tread designs. If most of your driving is on lower-speed city streets, then this won't be much of a factor. But for highway driving, you'll want to consider your options, especially if you're driving an SUV on pavement most of the time. A good salesperson will be able to tell you which tires are quieter among those you're considering; even those of the same make that are in a different line can vary in road noise.

That's the basics on tires, now we'll move on to wheels. Tires wear out, but wheels don't, so why would you want to change wheels? For many there's no reason to, especially when you look at some of the very attractive wheels that come on many of today's cars as original equipment. The way we see it, why would you bother to change wheels on such cars as a Corvette C6, late-model Mustang GT or Shelby GT500, or the 17-inch or 18-inch sport package wheels that come on the current 3 series BMW?

But, of course, some cars have hokey wheels that need to be turned into flowerpots. As such, one of the two main reasons most people consider a wheel change is simply for looks. A better-looking wheel makes a world of difference on many cars and trucks.

Besides appearance, the plus concept is a key reason to switch wheels. Plus sizing your wheels and tires is the best way to improve both the performance and appearance of your vehicle. By using a larger diameter wheel with a lower profile tire it's possible to properly maintain the overall diameter of the tire, keeping odometer and speedometer changes negligible. By using a tire with a shorter sidewall, you gain quickness in steering response and better lateral stability. The visual appeal is obvious; most wheels look better than the sidewall of the tire, so the more wheel and less sidewall there is, the better it looks. The idea of plus sizing is illustrated in the photos that accompany this story. Pretend that the four wheels we show you are for the same car, rather than the Focus, Miata, and two 3 Series BMWs they're actually mounted on. Two of the wheels (the Miata and Focus) are 15 inches in diameter, while the BMW 323iT (a wagon) and 328i have 16- and 17-inch wheels. If a car has a 15-inch wheel, then upgrading to a 16-inch wheel would be plus one and a 17-inch wheel would be plus two. You could also say that if a car has a 17-inch wheel (such as many performance cars do) then going to an 18-inch wheel and tire would be a plus one. If the car has 15-inch wheels, the 18s would be a plus three.

Besides plus sizing, other factors should be considered before shelling out big bucks for wheels. The benefits of a good-quality alloy wheel are numerous. And, of course, many cars come with them as factory original equipment. Either way, you end up with reduced unsprung weight compared to steel wheels. This is a factor affecting a vehicle's road holding ability. Unsprung weight is the portion of a vehicle that's not supported by the suspension (i.e. wheels, tires and brakes) and therefore is most susceptible to road shock and cornering forces. By reducing unsprung weight, alloy wheels provide more precise steering input and improved cornering characteristics. The added strength of a quality alloy wheel can also reduce tire deflection in cornering. This is particularly critical in a car equipped with high performance tires where lateral forces may approach 1.0g. Better brake cooling is another benefit. The metals in alloy wheels are excellent conductors of heat and improve heat dissipation from the brakes. The risk of brake fade is also reduced under more demanding conditions such as spirited driving on a twisty mountain road. Additionally, alloy wheels can be designed to allow cool air to flow over the brake calipers and rotors. The lighter rotational weight of alloy wheels can even provide a slight increase in acceleration and fuel economy.

These days it's tough to buy truly bad wheels and tires. While some wheels are lower quality than others, as is also the case with tires, there are so many good ones out there that you will usually have several possibilities from which to choose. As we've said here, be straightforward with what you really need and factor it in with that ever-present budget consideration and you'll be well grounded when it comes to keeping your car or truck on the ground.

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