Overview

1. Air Pressure
   
2. Identifying the Size of Tires on Your Car
   
3. Installing Your Wheels and Tire Packages
   
4. Load Range/ Ply Rating Identifications
   
5. Mixing Tires
   
6. Mounting and Balancing
   
7. Original Equipment (OE) Tires
   
8. P-Metric and Euro Metric Tire Sizes
   
9. Performance description
   
10. Run Flat Tires
    
11. Selecting the Right Tires
    
12. Sidewall Markings
    
13. Specific Mileage Warranties
    
14. Speed Rating
    
15. Storing Tires
    
16. Tires' Age and Wear
    
17. The Law
    
18. The Life of a Tire
    
19. Tire Warranties
    
20. UTQG
    
21. Wheel Alignment and Balancing
    
22. When Should I Replace My Tires?

1. Air Pressure

The main function of a tire is to carry the load of the car. Therefore, it is vital that correct air pressure is maintained. Over-inflation may cause a rapid and irregular wear.

Under-inflation will damage the tire structure leading to possible accidents. Improper air pressure will not allow the tire to function within its design. For best performance, maintain the air pressure recommended by the vehicle manufacturer and/or the tire manufacturer.

2.Identifying the Size of Tires on Your Car

The metric tire code consists of string of letters and numbers, as follows. For example tire size 185/60 R 14 82 H is means the following:

The aspect ratio is one of the sidewall heights to the total width of the tire, in percent. A 60 series tire, therefore, is a tire whose height is equal to 60% of its width. If the aspect ratio is missing, it is assumed to be 82%. If the number is greater than 200, it constitutes the diameter of the entire tire in millimetres.

An optional letter(s) is/are assigned to a tire, indicating the intended use of the tire or its vehicle class. The List of commonly used vehicle class markings is provided below:

3.Installing Your Wheels and Tire Packages

Installing tires and wheels correctly on your vehicle, will make your every drive a pleasant and safe one. Be it directional or asymmetric tire, make sure you check and position the tire the right way. We recommend setting every wheel and tire around your vehicle, so as to avoid mistakes. You should always install the new pair tires on the rear, and move the worn ones to the front, to keep stability on wet roads. Take into consideration the advice of a fitter, in case your vehicle requires different sizes.
Directional tires are designed to rotate in one direction only. The direction is indicated by the rotation arrow. Asymmetric tires can be used in any position on the vehicle by following wording such as 'inside' and 'outside' on the tire's sidewall.
Directional and asymmetric tire carry markings on the sidewall which show the correct direction of rotation and identify the side facing outwards. Before installing the tires, test fit each wheel in its final position! The owner's manual must provide you with the information for tire and wheel removal. We recommend the use of a four-way wrench or a socket on a breaker bar when removing lug nuts or bolts. Take into consideration the following:

• Always check the state of the vehicle's lug studs or wheel bolts, while loosening them, before reinstalling the wheels.
• Wheels have to fit flat against the vehicle's hubs.
• Do eliminate any devices such as stud clips, any rust and dirt from the hubs of brake rotors and drums. The large bolds holding Hyundai rotors need no removal!
• Make sure the last wheel's hub centering rings have been removed from the hubs, in case aftermarket wheels have been first used on the vehicle.
• If having drum brakes on the vehicle, verify that the wheel seats on the hub are not against the drum's outer flange or balance weights.

4. Load Range/ Ply Rating Identifications

"Load range" is a term that is synonymous with the term "ply rating" and is gradually replacing it. It relates to the actual load carrying capacity of the tire. The term refers to a specific tire with its maximum load as used in specific ways. Basically it is an index of tire strength and is expressed as a letter. The higher along the alphabet (A, B, C and up), the higher its load rating will be:

The load-index figures imprinted on the sidewall of the tire denote the maximum load capacity of a tire when driven at a maximum speed. The list of load indices and corresponding maximum speeds are listed below:

5.Mixing Tires

It is advisable not to mix different tire sizes or brand tires on the same axle, if not indicated by the tire or vehicle manufacturer, but use identical ones so as to keep the stability and safety of your vehicle.
The mixing of snow tires with summer, all season tires, of run-flat tires with non-run-flat tires on the same vehicle is not recommended under any circumstances.

If all tires of your vehicle get worn simultaneously, a new set of tires is required.  This is important in order to keep the handling balance that is engineered into the vehicle, while restoring poor weather fraction. You can purchase the exact same set proposed by you vehicle manufacturer, or a similar alternative. The tire size, tread pattern, compound of the tire, and the performance category should be identical as the original tires.

6. Mounting and Balancing

If you have decided to install new tires by yourself, read the below advices and have a look at "Tire &Wheel Package Installation" and "Proper Lug Nuts or Lug Bolts" for further information. The following recommendations are to be observed when mounting tires and wheels:

• Ask a professional to carry out the installing and balancing job!
• The wheel should have the right form and not be damaged.
• The tire beads must be securely mounted.
• No dirt between the hub and the wheel is allowed.
• The lugs must be correctly torqued.
• Make sure the wheel is securely seated on the hub.

Balancing means the distribution of the mass of the tire around the axle when mounted on its wheel and the car's axle. Balanced tires can determine the quality of a driving experience. An out-of-balance tire can shorten the tires' durability, the life of bearings, shocks, and other suspension components. A vibration appearing at 40-45 mph increasing speed, is most likely related to speed or the fact that the tire and wheel   assembly is not completely round. If this happens, contact the specialist to see, whether rebalancing will fix it.
Remember!
Only specialists should mount tires, so as to ensure safe operation. The tires should never exceed 40 psi (275 Kpa) and should be mounted only on designed diameter rims.

7. Original Equipment (OE) Tires

Your new car came with tires specifically chosen by the automobile manufacturer. Those tires weren't picked just because they were the right size and a familiar brand.  The manufacturer weighed the attributes of various tires and chose the best fit for your car's performance profile.

  If you have a high performance car, your tires were chosen for speed and handling. Certain touring cars are built for comfort, and the manufacturer called for tires that provide a smooth ride.  Some energy efficient vehicles need special tires designed for less road resistance and better gas mileage.

Tires are designed with various combinations of already mentioned and other attributes.  When your tires need to be replaced, many people believe, it makes sense to replace them with original equipment, to give you the ride and the performance that the automobile manufacturer intended.

Note:  When you replace your tires, it is always best to put 4 new tires on your car.  It is best to rotate your tires according to the manufacturer's schedule; otherwise, your tires probably won't wear at the same rate.  If that's the case, it's okay to replace just the two in the front or the two in the back.  For maximum safety, if you replace just two of the tires, it's best to purchase the same tires that are already on your vehicle.

8.P-Metric and Euro Metric Tire Sizes

P-Metric sized tires always have "P" at the beginning of their size description, such as P225/40 R18, while the Euro Metric tires just leave that out. Euro Metric tires are the older method for measuring tires, and began by using metric measurements for the tire's width. P-Metric tires were introduced to the United States in the late 70s for passenger cars and light trucks, and use an engineering formula to calculate the tire load capacity. This helps car manufacturers design new vehicles with tire standards.

9. Performance description

This is a designation at the end of a tire size that combines the load index followed by a single letter referring to the speed rating. Using 25/40 R18 92W as an example, 92W is the Performance description, with:

• 92 as the Load index
• The load indices of tires for passenger cars and light trucks are typically between 70 and 110
• An index of 80 can carry 992 pounds, 90 can carry 1323 pounds etc.
• W as the speed rating
• This rating is designated by a letter from M up to Z, and applies ONLY to undamaged and properly maintained and inflated tires.
• M is for a maximum speed of 81mph.
• S & T rated tires are for maximum speeds of 112 and 118 mph respectively, and are often used on tires for family sedans and minivans
• V if for a maximum speed of 140 mph and can be seen often with Sports sedans and coupes
• W & Y ratings are for more exotic sports cars and carry maximum speeds of  168 and 186 mph respectively
• Z speed ratings is an older designation and means the tires is rated for speeds over 149 mph

"Load range" is a term that is synonymous with the term "ply rating" and is gradually replacing it. It relates to the actual load carrying capacity of the tire. The term refers to a specific tire with its maximum load as used in specific ways. Basically it is an index of tire strength and is expressed as a letter. The higher along the alphabet (A, B, C and up), the higher its load rating will be:

The load-index figures imprinted on the sidewall of the tire denote the maximum load capacity of a tire when driven at a maximum speed. The list of load indices and corresponding maximum speeds are listed below:

The speed rating is designated by a letter from M up to Z, and applies ONLY to undamaged and properly maintained and inflated tires:

• M is for a maximum speed of 81mph.
• S & T rated tires are for maximum speeds of 112 and 118 mph respectively, and are often used on tires for family sedans and minivans
• V if for a maximum speed of 140 mph abd can be seen often with Sports sedans and coupes
• W & Y ratings are for more exotic sports cars and carry maximum speeds of  168 and 186 mph respectively
• Z speed ratings is an older designation and means the tires is rated for speeds over 149 mph

10. Run Flat Tires

Tires have always occupied a major place in giving a vehicle's convenience and safety.
The tire manufacturers' constant engagement in research have upgraded  tire durableness and lately  have  succeeded in designing  tires which are able,  for a limited time, to maintain vehicle mobility by using standard Original Equipment and aftermarket wheels. The run flat tires offer the driver the chance in deciding where to have tire repairs made.

It's not the tires carrying the weight of the vehicle but the air inside them. The load capacity of a tire is determined by the following aspects: the size of the air chamber between the tire and wheel, the tire's construction to hold air pressure, the amount of air pressure in the tire.

There are three basic technologies currently available to keep vehicle's mobility when a tire is deflated: self-sealing, self-supporting and auxiliary -supported tires.

Self supporting tires are created with a stiffer internal construction that can temporarily bear the weight of the vehicle even when the pressure within the tire is greatly reduced. So as to provide self-supporting capacity, the tires attach rubber inserts next to or between layers of heat-resistant cord to prevent the breaking of reinforcing cords in case of loss of air pressure. The bead around the edge of the tire is also specialized to grip the wheel rim such as to avoid becoming detached from the rim. Besides, they feature beads that allow the tire to strongly grip current Original Equipment and aftermarket wheels even in the event of air loss. Self supporting tires require a tire pressure monitoring system to alert the driver that they have lost air pressure so as to avoid further tire damage by failing to inflate or repair the tire. Generally, self-supporting tires provide for the vehicle to drive for 50 miles at around 50 miles per hour

Self-Sealing tires are built to permanently fix most tread punctures. The tires contain an extra lining within the tire that self-seals in the event of a small hole due to a nail, bolts or screw up to 3/16 of inch in diameter. They provide a seal around the object when the tire is punctured and then fill out the small hole in the tread when the object is removed. This way, the loss of air is prevented from the outset such that the tire is either permanently self-repairing or at least loses air very slowly. Self-sealing tires do not require a low air pressure warning system.

Auxiliary Supported Systems combine special wheels and tires used for Original Equipment vehicle applications. In the auxiliary supported systems, the flat tires tread rests on a support ring attached to the wheel when the tire loses pressure this type of system offers the advantage of placing most of the mechanical task, thus providing run flat capability on the wheel and minimizes the responsibility of the tire. These systems generally offer better ride quality because of their sidewall's stiffness, which can be equivalent to a standard tire, but the requirement to have both unique wheels and special tires and limit them from widespread use. Example: Michelin's PAX System wheels and tires

11. Selecting the Right Tires

It is crucial to choose an appropriate type of tires for your vehicle. Below are listed several recommendations that will help you make a good selection or tires suitable for your car:

• All the tires on your car should be as similar as possible, so as to avoid handling problems and maintain the performance of your vehicle. For example, one end of your vehicle may not respond as fast as the other one does, thus making the vehicle more difficult to control.
• If one tire needs replacement, it should be changed with a tire that perfectly matches the others as far as the brand, line, size and speed rating are concerned.
• When changing two tires because of damage or worn out, the replacements must be placed on the rear axle. Choose some tires that best suit the current ones. Identical new tires would be the best choice, but others of the same type, size can fit well.
• When it comes about replacing all four tires, you can freely make a choice from another tire category. For longer lasting tires providing a smoother ride, optimized performance, you should search for a category description that meets your expectations. If you like and wish to stick to the original type, just replace them.

Switching to tires of a different size than the original equipment may have serious implications, and is not recommended.
The most important feature of the tire you select is the ability to carry the weight of the car. NEVER undersize!
The other thing to be considered is the overall tire diameter. A 3% diameter change is preferable for cars and vans. Sport utility vehicles and pick-ups are generally designed to handle up to a 15% oversize tire. By checking "Calculating the Tire Dimension" you can find information on how to calculate your tire dimension. A 3% diameter increase or decrease in tire diameter may look like limiting, but in many of the cases, it permits about a 3/4" change in diameter.
We have created the Plus Sizing System for your convenience, so as to help you selecting the appropriate tire width that ensures adequate load capacity, by taking into account the diameters of the available tires and wheels.

Different driving conditions require different types of tires. To fully and successfully meet each of the driving conditions requirements - be it sunny, rainy, or snowy weather - you should decide based on a performance category. If you are going to use summer tires in the summer and snow tires in the winter, you can choose those that best meet your expectations. When selecting one set of tires for all year round, you will likely get a high quality drive all year around, however, your vehicle's capacity will be compromised under the worst weather conditions.
For short trips, almost any tire is acceptable. If you drive your vehicle in the city or in the freeways, you will be pleased with tires that are sensitive and highly responsive. If you drive mostly on interstate highways, you will need long-lasting, quiet, and smooth tires. For fast driving on twisting roads, you should select a tire that features good handling. If you drive on autocross events, you will desire the best competition tires.
Always balance the requirements of your driving conditions. If you get snow infrequently, you may want to select an all-season tire. If you often drive under worse weather conditions, or ones different than those you are familiar with, you should think about selecting two sets of tires. Each set will be designed to meet the particular weather conditions, and thereby fulfill your expectations under any weather conditions.

You may wonder why the price of tires exceeds the cost of fuel for your vehicle. When purchasing tires for your vehicle, you should think about the purchase as a long term investment in the quality of your drive, and evaluating the cost in terms of "tire per mile". Why? By systematically tracing our total cost, we found that the total fuel costs of 10-20 thousand miles surpass an average tire price.  In this context, it should be emphasized that the quality of your drive is very closely connected with the performance of your tires. In fact, the correlation between the overall quality of your drive and the performance of your tires is much greater, than the one between the quality of your drive and the type of fuel that you use.

12.  Sidewall Markings

The manufacturer provides us with a lot of information on the tires' sidewalls, most related to the their basic dimensions, identifying the week of production, the materials used to strengthen the rubber, the load, and  tire's maximum inflation pressures. Some other information confirms that the tires meet diverse industry standards and government regulations of the nations, in which they are used.

The List of Used Sidewalk Markings is provided below:

13.  Specific Mileage Warranties

Tread-wear warranties seem have a limited warranty, and the consumer has to fulfill maintenance requirements to keep them in force. The tread-wear warranty applies to the original owner and the original vehicle only. The consumer is asked for the proof of purchase and the original installation date, as well as documentation that the tires were correctly inflated, rotated, and aligned, and that worn suspension components were replaced. If the tires' worn appearance shows that they were not kept in proper condition, the tire manufacturer will reject the Tread-wear warranty.
How do consumers receive their value, if the tires were properly maintained?

Today, the majority mileage tread-wear warranties vary from a low of 30,000 miles to a high of 80,000 miles. If the tread depth was worn down to 2/32 of an inch in 30,000 miles on a tire with a 40,000 mile tread-wear warranty, the consumers would be offered a new set of tires of the same brand that would be discounted from their current retail price by 25% (prorating the 10,000 of the 40,000 miles of wear they did not receive). The consumer is then required to pay the difference between the warranted mileage and the mileage actually received as they purchase their replacement tires.

 If the tires wear out within 3 years from the date of purchase, the consumer is required to pay 50% of the current retail price for Bridgestone and Goodyear tires, and a proportional cost based on the number of months of actual service received vs. the 72 months (6 years) warranted by Michelin.

Another issue some consumers may raise regarding the mileage warranties is that the tires must be worn down to the tread-wear indicators before replacement under the warranty.  The tires must be at or near the 2/32 inch of remaining tread depth which is the minimum allowable legal tread depth, as when tires are "worn out." The problem the consumer may deal with is the treadwear warranty against traction.

14. Speed Rating

This rating is designated by a letter from M up to Z, and applies ONLY to undamaged and properly maintained and inflated tires:

• M is for a maximum speed of 81mph.
• S & T rated tires are for maximum speeds of 112 and 118 mph respectively, and are often used on tires for family sedans and minivans
• V if for a maximum speed of 140 mph abd can be seen often with Sports sedans and coupes
• W & Y ratings are for more exotic sports cars and carry maximum speeds of  168 and 186 mph respectively
• Z speed ratings is an older designation and means the tires is rated for speeds over 149 mph

15. Storing Tires

To correctly store tires that will not be used continuously, we recommend the following:

• Never store a vehicle with weight on its tires for long periods of time.
• Avoid direct sunlight on tires whenever possible.
• Clean each tire from brake dust, dirt and grime, before storing. 
• Do not apply tire dressings on them.
• Avoid any moisture and remove as much air as practical, and place each tire in its airtight plastic bag for storing to help reduce oil evaporation and then cover the sealed bag with a Tire Tote.
• Store white-to-white and black-to-black tires to prevent staining the white rubber, if not kept in plastic bags.
• Stack all tires white sidewall up to allow the oils from each tire's black sidewall to migrate into the white rubber of the tire below it.
• Keep the tires in a cool, dry places preferably  in a dry basement or climate-controlled workshop to avoid hot and cold temperatures, as well as seasonal precipitation and humidity.
• Store the tires away from sources of ozone, devices such as motors, furnace, sump pump
• Do not store the tires near sources of ozone.  Keep your tires away from the furnace, sump pump, etc.

While tires will age somewhat regardless of what precautions are taken, these procedures will help slow the process compared to taking no precautions at all.

16. Tires' Age and Wear

Over the years, it has become clear that tires can" age out" as well as they wear out. The U.S. National Highway Traffic Safety Administration and tire manufacturers are currently studying the many variables on how long will tires last before aging out. Environmental conditions like exposure to sunlight and coastal climates, as well as poor storage and infrequent use, accelerate the aging process, but the issue of how to confirm and quantify the aging still remains.

The recommendations of industry associations regarding inspecting and replacing tires due to age come from outside the United States.

According to The British Rubber Manufacturers Association (BRMA) practice issued June, 2001 the unused tires should not be used if they are over six years old, and all tires should be replaced ten years from the date of their production.

By the practice issued in May, 2005 The Japan Automobile Tire Manufacturers Association (JATMA) encourages the customers to have their vehicle tires ( spare tires as well)  promptly inspected after five years of use so as  to determine if the tires can still be used. It recommends that all tires including the spare tire ones that were made more than ten years ago be replaced with new tires.

Various European vehicle manufacturers of high performance sports cars, sedans and coupes inform that tires older than 6 years should not be used under any circumstances. It is though to be noted that European recommendations must consider the driving conditions that include roads like the German Autobahn, which permits vehicles to be legally driven at their top speeds for considerable periods of time.

The U.S. divisions of DaimlerChrysler and Ford Motor Company joined their European partners in 2005 by advising the tires should be replaced as Original Equipment after 6 years of service.

Many of the tires we offer are manufactured in Europe or Asia and may have six to nine months old. It may also happen that the tire producer's minimum run quantities will manufacture enough tires to meet a few years of consumer demand for lower volume types and sizes. And in these cases the tires we receive directly from the manufacturer may already be several years old. When it comes about helping a tire manufacturer clear a discontinued tire line, the tires are offered at a significant discount and will most probably be worn out within their useful lifetime.  Most of the tires we ship are no older than a year or two.

It is always to remember that the tires' tread with an aggressive compound have shorter live. As a general experience, most street tires' useful life is between six to ten years.

17. The Law

1. Tires on cars, light vans (not exceeding gross weight) and light trailers must have a tread depth of at least 1.6 millimeters across the central three-quarters of the breadth and in a continuous band around the entire circumference of the tire.
2. Tires must be suitable (i.e. of the correct specification and size) for the intended use of the vehicle.  Additionally, tires must be inflated to the manufacturers' recommended pressures.
3. Tires of different types must not be fitted to opposite wheels of the vehicle (for example, radial-ply tires must not be fitted to a wheel on the same axle as wheels already fitted with cross-ply tires and vice versa. A two-axle vehicle must not have radial ply tires on the front axle if cross ply tires are fitted to the rear axle.)
4. No tire must have a break in its fabric or a cut deep enough to reach the body cords. No cut must be more than 25 millimeters or 10% of the tire's section width, whichever is greater.
5. There must be no lump, bulge or tear caused by separation or partial fracture of its structure, neither must any portion of the ply or cord structure be exposed.

18. The Life of a Tire

It is quite simple to establish when a tire was manufactured, by following the Tire Identification Number, which is the batch code marked on the tire sidewall referring to the week and the year of manufacture.

As per the U.S. Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) requirements, the Tire Identification Numbers combines the letters DOT, and a grouping of numbers and letters with up to 12 digits, designating the location of production, tire size and manufacturer's code, date of manufacturing.   

Ever since 2000 and up to now, the last four digits of the Tire Identification Number have indicated the week and year the tire was built (2 digits indentifying the week, the other 2 the year). The complete Tire Identification Number has been generally requested to be marked on one sidewall, but according to the current regulations, the DOT and the first digits of the Tire Identification Number must be molded on the opposite sidewall as well.

For tires manufactured before the year 2000, a three-digit code was used (first two numbers indicate the week, while the last number, the year). Tires manufactured in the 1990s may carry a little triangle (Δ) that should be found after the DOT code and identifies the decade.

19. Tire Warranties

Each manufacturer establishes the period of time they repair or replace defective products due to materials and workmanship.   Tires are typically backed by their manufacturer's limited warranties for a period of 4 to 6 years from the date of purchase or until the tread wears out.

The duration of the tires' limited warranty is specified by each manufacturer.  Tire warranties begin at the time of delivery for new vehicles, and at the time of purchase for replacements. As a result, a new vehicle's registration certificate or the replacement tire's sales invoice will establish proof of ownership and the tire's in-service date. If no proof of purchase is available, the week and year the tire was manufactured will be used.

When the tire's original tread is worn down to 2/32nds of an inch (1.6 mm) of remaining tread, tire warranties also expire.

Tread-life Warranties

Due to the variety of driving surfaces and conditions and geographic influences in the United States, not all consumers receive the warranted treadlife mileage. As the vehicle manufacturers decide not to purchase the original equipment from the tire manufacturers, treadlife/mileage warranties do not apply to tires fitted as Original Equipment on new vehicles. Treadlife warranties on replacement tires only hold for the original owner and vehicle upon which the set of tires was initially mounted.

Uniformity Warranty

Tire balance and internal forces are measured during a tire's final inspection at the factory. Therefore, remember that none of the tire manufacturers accepts the idea that all four tires from the same vehicle are out-of-round or responsible for a vibration.

If a new tire contributes to a vehicle ride disturbance because of materials or workmanship, it will be corrected as soon as possible and replaced before the first 1/32- to 2/32-inch of treadwear or during the first year of service.

Ride disturbances that occur after this initial period are connected to road hazard damage or irregular wear stemming from the vehicle's mechanical condition and/or lack of routine maintenance.

Workmanship & Materials Warranty

In the first year of ownership or 25% of the tire's treadwear, the tire will be exchanged free of charge for the customer, excluding freight. For the rest of the tire's warranty period, the cost of replacement is prorated by crediting the owner for the percentage of service not received.

Manufacturer Road Hazard Warranty

No tire is indestructible, thereof while road hazard injuries or impact damage caused by potholes, curbs or other objects in the road, the tire damage they inflict is not within the control of the tire manufacturer and is not typically covered by their limited tire warranties. Only some  tires remain backed by a tire manufacturer road hazard warranty, such as Michelin's ZP Assurance Plan covering Michelin Self-Supporting Zero Pressure (ZP) run flat tires. But because many drivers desire the financial security that a road hazard program provides, tires-easy offers an economically priced, optional Tire Road Hazard Service Program to our retail customers.

Manufacturer Special Warranty - 15 days Test Drives/Trials

A retail customer can return the unwanted tires within 30 days of purchase for a full refund or exchange. (Freight excluded). Proof of purchase is requested.

The 15 days Test Drives/Trials do not cover the tires received as original equipment on new vehicles.

20.  UTQG: The Uniform Tire Quality Grading System

To help consumers evaluate their tires, the U.S. National Highway Traffic Safety Administration (NHTSA) created the Uniform Tire Quality Grading System (UTQG). The UTQG rates tires are rated on their tread-wear, traction performance, and temperature resistance. The grade for each of these can be found on the sidewall of your tire (except for winter tires and certain light truck tires).

Tread-wear

The UTQG tread-wear grade indicates how long your tire tread will last in relation to other tires. For instance, a tire with a grade of 400 will last twice as long as a tire with a grade of 200, according to how it performed in the tread-wear test.  Note: Actual tire performance can differ greatly for many reasons, including driving style, climate, tire inflation and vehicle weight.

Traction

The UTQG traction grade rates the ability of your tire to stop on wet pavement. Traction performance is assigned one of the following grades, which you will find on the sidewall of your tire:
AA, A, B, C. Tires with an AA grade stop the fastest on wet pavement,  C graded tires the slowest.
CAUTION: The UTQG traction tests do not test tires for cornering, acceleration, driving at high speed or driving on dry roads. Tires are tested with straight ahead braking only.

Temperature

The UTQG temperature grade indicates the ability of your tire to dissipate the heat generated by driving. Over time, heat can cause damage to your tires. Temperature resistance is given one of A, B or C grade, which you can locate on the sidewall of your tire. All tires sold in the United States must have at least a C rating.
CAUTION: The tires in UTQG tests were inflated properly and the vehicles were not overloaded. Excessive heat can be produced by under-inflation of your tires, driving at high speed, driving an overloaded vehicle, and certain road and weather conditions.

21. Wheel Alignment and Balancing

A major cause of rapid tread wear is improper wheel alignment and balancing. Abnormal noise, vibration and harshness of steering are a signal that alignment and balancing may be improper.

22. When Should I Replace My Tires?

The U.S. law for most states holds that tires are legally worn out when they have worn down to 2/32" of remaining tread depth. It is important to acknowledge that when tire wears out its capacity to perform in the rain and snow will diminish. At 2/32" of remaining tread depth, resistance to hydroplaning in wet conditions has been reduced, and traction in snow has been removed.

If driving on rain and wet roads, you should think about changing your tires when they reach approximately 4/32" of remaining tread depth. You need enough tread depth to disperse water through the tire's grooves. Otherwise the vehicle's tires will lose traction.  

When driving in snow, you should consider changing the tires when they reach approximately 6/32" of remaining tread depth, in order to maintain a good stability. More tread depth is needed in snow, as the tires need to compress it in their grooves and release it while rolling. If not enough tread depth is remaining, the traction will be substantially diminished.

Tread depth is an important element for snow traction, thus winter tires are equipped with tread depths deeper than standard all-season or summer tires. Some winter tires even have a series of wear bars molded in their tread pattern indicating approximately 6/32" remaining tread depth.

The usual method of determining when it's the right time to get new tires is the Lincoln penny tread depth test. If your tread gets below 2/32 'your tires' ability to grip the road in unfavorable conditions is greatly reduced.

The traction between the tires and the road provides the driver the ability to have a control over the vehicle.  Tires do not need tread designs or much tread depth to create traction on dry roads but do require tread designs to channel water and slush from between the tire and the road, as well as provide edges with good grip on snow.

While driving at high speeds, the air the tires encounter can easily be compressed and moved out, but not the same thing applies to the liquids.  The tires' tread designs and tread depths as well as the adverse rainy conditions depths decide if the tires are forced to hydroplane and how quickly they can stop a vehicle.

A general passenger car tire begins with about 1/3" of tread depth and a footprint surface of around twenty inches the most of it being composed of rubber that grasps the road and grooves that create the tread design.  The tire tread will slowly wear away and the amount of grooves reduce without even observing until the point the car will not stop on wet short distance roads.

You should think about replacing your tires when they reach about 4/32" of remaining tread depth in case of rain and wet roads, and change them when they get to  about  6/32" of remaining tread depth in case of snowy roads for the good tire adhesion performance and good mobility of your vehicle.

Always replace the tires before the legal limit so as not to compromise your safety and save the money you would loose for repairing!