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WheelTire Classroom

Modern tire technology blends a unique mix of chemistry, physics and engineering to give tires a high degree of comfort, performance, fuel efficiency, reliability and safety. Many tires are custom-designed to meet the stresses and performance needs of a specific vehicle or climate.  If properly cared for, tires can provide thousands of reliable miles.

Tire Construction

                         Typical Components of a Tire 


Tire Basics

Service Description

Load Index

Speed Rating


 Types of Tires

All-Season Tires

Winter Tires

Summer Tires

Run-flat Tires


Service Description


Each tire has a service description imprinted on the sidewall which is used to describe combined load index and speed rating of that particular tire.  Examples are shown below:


Service Description

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Load Index

The load index refers to the amount of weight a tire can support at the maximum inflation pressure imprinted on the tire sidewall. It is critical that the load index of replacement tires is equal to, or greater than, the load index requirements set by the vehicle manufacturer.  Failure to have the appropriate load carrying capacity can result in overloading and eventual tire failure. 

Since 1968, cars and light trucks sold in the U.S. have been required to have a tire information sticker, called a placard.  The placard indicates the size of the original equipment tires (including the spare), cold inflation pressure for the tires on both axles as well as the spare, and load capacity.  Depending on the vehicle, the tire placard will either be located on the edge of the driver's door, the doorpost, glove box or fuel door.  If the tire placard is missing, consult the owner's manual, vehicle manufacturer, or tire manufacturer regarding applicable tire information.

Tire Placard(1)

                                                  Sample Tire Information Placard


The table below illustrates the load index value in pounds (lbs.): 

Load Index Table

Load Index Chart

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Speed Rating

The speed rating of a tire indicates the speed category (or range of speeds) at which the tire can carry a load under specified service conditions. The speed rating system used today was developed in Europe in response to the need to control the safe performance of tires at standardized speeds. A letter from A to Z symbolizes a tire's certified speed rating, ranging from 5 km/h (3mph) to above 300 km/h (186 mph). This rating system, listed below, describes the top speed for which a tire is certified. It does not indicate the total performance capability of a tire.

When this speed rating system was originally developed, the Unlimited V category of over 210 km/h (130 mph) was the top speed rating a tire could achieve. As manufacturers made more tires that did not fit this category, it was necessary to better regulate performance at standardized speeds to ensure safety. The Limited V category of 250 km/h (149 mph) was then created, and the Z speed rating was added as the top speed rating that a tire could achieve. W and Y limited speed symbols have been added as higher speed categories.

Always consult the manufacturer for the maximum speed of Unlimited Z tires. Speed rating is identified as a part of the tire's sizing or service description. For tires having a maximum speed capability above 240 km/h (149 mph), a "ZR" may appear in the size designation. For tires having a maximum speed capability above 300 km/h (186 mph), a "ZR" must appear in the size designation. Consult the tire manufacturer for maximum speed when there is no service description.

Speed Rating Values: 


                                 B - 31 mph (50 km/h)                    Q - 100 mph (160 km/h)

                                 C - 37 mph (60 km/h)                    R - 106 mph (170 km/h)

                                 D - 40 mph (65 km/h)                    S - 112 mph (180 km/h)

                                 E - 43 mph (70 km/h)                     T - 118 mph (190 km/h)

                                 F - 50 mph (80 km/h)                     U - 124 mph (200 km/h)

                                 G - 56 mph (90 km/h)                    H - 130 mph (210 km/h)

                                 J - 62 mph (100 km/h)                   V - 149 mph (240 km/h)

                                 K - 68 mph (110 km/h)                   Z - over 149 mph (240 km/h)

                                 L - 75 mph (120 km/h)                   W - 168 mph (270 km/h)

                                 M - 81 mph (130 km/h)                 Y - 186 mph (300 km/h)

                                 N - 87 mph (140 km/h)                 (Y) - over 186 mph (300 km/h)

                                  P - 94 mph (150 km/h)




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DOT Number / Tire Identification Number

One of the most important pieces of information on the sidewall of a tire is often referred to as the DOT number (code) or Tire Identification Number (TIN).  The DOT number or TIN is used to identify production runs and is different than a serial number which is a unique code assigned for identification of a single unit.  The three letters "DOT" followed by eight to twelve characters indicate that the tire has passed all of the tests required by Federal motor vehicle safety standards and can be used in case of a recall.

The first group of two letters or numbers represent the assigned identification mark for the manufacturer's plant.  The second group of two characters identifies the tire size.  The third group can be no more than 4 characters may be used at the option of the manufacturer to indicate the tire type, design spec, compounds or other significant characteristics of the tire.

The final four numbers of the DOT code represent the date of manufacture.  The first two numbers reflect the week and the last two indicate the year.  So, a tire whose DOT number ends with 4313, was manufactured in the 43rd week of 2013.

DOT Numbers


Types of Tires


All-Season Tires:

   1)  Mud and Snow (M+S) Rating: All-season tires are branded with the M+S symbol, meaning they have met the Rubber Manufacturers Association's (RMA) requirements for an all-season tire. These tires are designed to provide year-round traction on wet and dry roads (including light snow).  If you're looking for all-season traction, make sure your tires have the M+S symbol on the sidewall.     


   2)  Severe Snow Use Rating:  A step up from the M+S rating, these tires have met the RMA's requirements for use in severe snow conditions.  Tires rated for severe   snow use will have a 'mountain and snowflake' image imprinted on the sidewall.  


All-Season Tire Ratings


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Winter Tires: 

As the temperature drops below 40-degrees Fahrenheit, tire rubber hardens, significantly reducing grip with the road.  The good news is that winter tire technology has come a long way in recent years to provide excellent winter traction, ice grip, and ride comfort. Rubber compounds in winter tires are designed to stay softer at cold temperatures.  This gives the tire much needed flexibility to 'grab' the road with the thousands of 'biting edges' provided by the sipes or cuts in the tread.  Winter tires can be categorized in three groups:

  • Studdable Winter Tires:  These tires are designed to accept dozens of metal studs which can be installed using a tire studding machine.  These metal studs provide the ultimate in winter traction, especially on ice.  
  • Studless Winter Tires:  These tires are designed to provide the best balance of winter traction with ride comfort.  These tires rely on the cuts, or sipes, in the tread to provide thousands of 'biting edges' when the tire comes in contact with the road. 
  • Performance Winter Tires:  Designed for maximum winter traction while maintaining high-speed performance characteristics.  These tires provide supurb steering response, ride comfort, and grip in all types of winter conditions.


                                          Studdable                                                  Studless                             

Studded Winter Tire    Studless Winter Tire Real



Performance Winter Tire Real



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Summer Tires: 

Maximum traction on wet and/or dry roads is what summer tires are designed for.  These tires may be used in the spring, summer, and fall, but are not intended for use in cold weather (including snow and icy conditions).  You'll notice the tread on a summer tire looks smooth compared to a winter or all-season tire.  This enables the tire to grip more of the road surface, but hinders it from gripping well on snowy or icy surfaces.  If you drive your vehicle in winter conditions, you should have a set of winter or all-season tires to compliment your summer tires.     

Summer Tire

Summer Tire


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Run-flat Tires:

Run-flat tires are designed with much thicker sidewalls than conventional tires, enabling them to support the weight of the vehicle even when completely deflated.  Run-flats are not only capable of operating without air pressure for 50-200 miles at 50-55 MPH (depending on the tire), but are also able to maintain virtually the same level of ride comfort and handling.  Any vehicle using run-flat tires must come equipped with a tire pressure monitoring system (TPMS), since any loss of air pressure would go unnoticed by the driver. 

Runflat TireRun-flat tire construction  

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Snow Tires

Why 4 Snow Tires? 

The purpose of installing winter tires is to optimize traction and handling in both adverse winter situations as well as ideal road conditions.

There is a significant difference in traction between snow tires and all season or performance tires.  Placing snow tires on only the front or rear of your vehicle can create an imbalance in the handling of your vehicle.  One end of the vehicle will not perform the same as the other.

We all have seen or heard spinning tires in the snow.  While it is important to have enough traction to accelerate in the snow, it is vital to have the traction needed to brake and increase your vehicle’s handing in wintry conditions.

For the benefit and safety of our customers, Sullivan Tire is following the recommendations of tire manufacturers and industry experts:

  • Studded snow tires must be applied to all four (wheel) positions.
  • Winter tires must be applied to all four (wheel) positions on front-wheel drive vehicles.
  • Winter tires can be applied to the rear wheel positions on rear wheel drive vehicles.
  • Never put non-radial winter tires on the rear wheel positions if radials are on the front, except when the vehicle has dual wheels on the rear axle.

There have been tremendous improvements in traction control.  ABS brakes and Traction Control systems have improved handling in many of today’s vehicles.  However, these systems do not improve your tire’s traction, and your tires are the only part of your vehicle that makes contact with the road.

We have given careful consideration to the above recommendations and have decided it is in the best interest of our customers and the motoring public to follow this policy.  Please do not ask us to violate it.

We appreciate your business and apologize for any inconvenience.

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