How to Buy
Your vehicle was designed to use a specific tire size in order to support the weight of the car, the passengers and cargo for its intended use. You should select replacement tires that are the same size and load carrying capacity as your original tires. Vehicle manufacturers do allow an optional tire size on some models for extra load carrying capacity or to improve handling. Sources for optional sizes include your owner?s manual and tire manufacturer?s fitment guides. Fender clearances, load carrying capacity, proper rim width diameter and overall tire diameter are all considerations. The concept of changing a tire shape and its rim diameter by 1 or 2 inches or even more, was developed to allow a tires shape to be changed but maintain the same carrying capacity and approximate overall diameter. The changes in the tire shape or, greatly affect the tires appearance and performance. It's easy to see that a shorter sidewall and wider tread on a wheel that is 2 inches larger in diameter improves vehicle appearance. The performance changes that go along with this appearance change include, improved steering response (handling), better stopping and a stiffer ride.
The load carrying capacity of your tire is determined by its size and load range. The size of the tire determines the size of the air chamber and the load range sets the maximum cold inflation pressure allowed. These size and pressure factors determine a tire's ability to carry a load for a given operation condition. Always maintain load capacity. Hint: A lot of pick-ups and Suburbans come with P235/75R15 EXTRA LOAD. Don't make the common mistake of replacing them with P235/75R15 STANDARD LOAD tires.
Passenger tire tread designs are basically categorized by Highway (rib), all-season and winter, with each one having progressively more traction. Light truck tires on the other hand, have six basic tread types. They include: all-season, all terrain, commercial highway, commercial traction, high performance, and mud traction. The area of the country you live in and the kind of weather and terrain you drive in, loads carried and driving habits generally determine which tread type is best for you. Most car owners choose an all-season tread design. Most individual pick-up owners usually purchase the all-season (more highway characteristics) or the all-terrain (more off road traction) tread designs. For commercial vehicles, commercial highway and commercial traction tread designs best meet tread life and even wear requirements for vehicles carrying heavy loads and/or in hard use applications. Mud terrain treads are reserved for extreme condition and off the road enthusiasts. High Performance LT tires are for the driver who wants their pick-up or SUV to handle more like a sports car and/or wants the popular wide-tread, short-sidewall styling.
Speed rated tires used to be limited to tires for high performance vehicles. When the public started wanting the better handling of the performance cars for the family car, speed rated tires became standard equipment for most vehicles. The new standard for speed rating includes a load index that precedes the speed rating as part of the size. Example: Size P235/75R15 104S. The load index is 104 preceding the speed rating ?S? and in most cases the load index equals a tires load carrying capacity at rated speed when inflated to the maximum inflation. The most common speed ratings are S,T,H,V, and Z. This combination of load index and speed rating are located near the size markings on the sidewall. The handling and stopping ability of tires generally improve greatly as speed rating goes up. Because the main benefit of a higher speed rating is that it provides drivers improved handling and stopping. It is best to think of speed rating as a performance rating. While an SR has a maximum sustainable speed of 112 mph; it is better to think of SR as meaning standard performance. Similarly, HR (130 mph max) should be thought of as high performance, VR (149 mph max.) should be thought of as very high performance, and ZR as ultra high performance. The same or higher speed rating should always be purchased to maintain the handling and stopping performance designed into your car for safety. It must be noted that a higher speed rating will improving handling and stopping usually results in a firmer ride and lower tire mileage.
Believe it or not, there are "fashion" trends in tire sidewall styling. The white sidewall stripe is traditional style, but designers change the width from time to time. Black sidewalls, smooth, sculptured, raised and/or serrated letters have become more and more popular for performance tires and for light truck tires. Black as well as Raised White Letter and Raised Outline White Letter are also popular. Style availability depends on the tire size, speed rating and the vehicles these tires were typically designed for. Style is always a personal preference.
BRAND & QUALITY
There are many different brands to choose from. The major brands are household names because they are highly advertised. But just because a brand isn't well-known, doesn't mean the tire isn't as good. Differences between brands in many cases are smaller than the differences between tire lines within the same brands. The better products of the same size and speed rating within a brand generally cost more initially but cost less per mile and also have better stopping and handling performance. The ride comfort and road noise generated by tires varies from line to line as well as brand to brand. If you prefer a certain brand don't assume that brand name alone will give you what you want from a tire, you must choose the proper tire within that brand that best meets your tire needs. Compare the Uniform Tire Quality Grading (UTQG) information for each brand of tires you are considering. The treadwear, traction, and temperature resistance grades listed can help you evaluate each tire. Make sure you compare tires with similar features (i.e., all season treads, speed ratings, premium construction, etc.). The treadwear grade can be used to estimate mileage. Take the grade number of 300 and multiply by 150 mile per grade point and you would get 45,000 miles. (Treadwear grade x 150 miles per grade point = expected miles). This is the number of miles that can be reasonably expected from a tire when used in non-commercial service with a good driver and good maintenance. The traction rates wet and straight ahead stopping on two different road surfaces. All tires must pass this test but ?A? and ?AA? ratings mean that a tire has superior wet stopping ability. Temperature rating is a tires resistance to heat and ability to dissipate any heat that builds up. Tires fail when they get too hot. The most common cause of elevated tire operating temperatures is overloaded or low air pressure and high speed driving. All tires must pass the minimum standard "C" rating and for most users this is very adequate. Temperature ratings become more important in commercially used tires, tires going flat, and high performance tires. Most high performance HR and higher speed rating tires have a temperature rating of "A" or ?AA?.
YOUR DRIVING NEEDS
Tread life is important to every driver. If you are going to keep your car for a long time or long enough that you don't want to have bald tires when you trade or sell your car, a longer life tire makes sense. If you drive at very high speed a tire that will stay together at these speeds and have maximum traction in cornering is more important. A quiet ride is also important to most drivers. Is a quieter ride more important than maximum traction or a lower initial price? You must decide. All drivers have that occasional need in driving to make an emergency stop to avoid an accident or a need for good handling to avoid a pothole. Aggressive drivers, who like to take that corner on the traction edge or push the performance level of their tires, need tires that handle and stop better than other drivers. Quality or how well a tire delivers the above benefits compared to other tires is important. Brand names are not necessarily assurance of quality; check with consumer publications and tire professionals. Low cost can either mean low initial cost or low cost per mile, but in either case the tire you're purchasing should at least meet the minimum that is acceptable to you for your driving needs.