Tire Technicals

Tire Sizing

Passenger Tire sizing is typically displayed as:

P215/65R15 89H

• The "P" stands for "P-Metric" or "Passenger". This means that it is a North American tire sizing designation. European tires typically don't have the "P" attached to the size. Tires with higher ply ratings will generally start with "LT" which stands for "Light Truck". This indicates the tire is an LT metric and will always have a Load Range indicated. It is important to note this for vehicles that call for LT metric tires. Never substitute a P metric tire for an LT metric tire, even if all the other dimensions are the same.

• The "215" is the width of a tire, also known as the "section width". This is the width of the tire in millimeters at its widest point from sidewall to sidewall when mounted on the recommended rim width. The actual tire width can vary depending on the rim width it is mounted on.

• The "65"is known as the Aspect Ratio. It is calculated by dividing the section height by the section width and multiplying by 100. (In this example, the sidewall will be 65% of 215)

• The "R" stands for Radial, meaning it has a radial construction. Radial tires have ply cords that extend to the beads and are laid at 90 degrees to the centerline of the tread, the carcass being stabilized by a circumferential belt. Other possibilities include "B" for belted construction and "D" for diagonal construction. This means the ply cords extend to the beads and are laid at alternate angles less than 90 degrees to the centerline of the tread.

• The "15" stands for the diameter of the wheel in inches. This is the exact size that this tire will fit. There are some older rims called "TRX" which are metric measurements like 390. You CAN NOT mix TRX rims with regular tires or vise-versa.

• The "89" is the load index

• The "H" is the speed symbol.

Speed Ratings

The speed rating of any tire is a measurement of the top safe speed the tire can carry a load under specified conditions. It is also an indication of how the tire will handle at lower speeds. A higher rated tire will give you better traction and improved steering response even at 50mph.

Below is a listing of common speed ratings:

It is not recommended to downgrade your tires to a lower speed rating than of the OEM tires that came with your vehicle at the time of purchase. Doing so can effect the handling of the car, and in an emergency situation that can be dangerous. Also, never mix tires with different speed ratings on your vehicle.

Load Ratings

The load rating for any tire (load index) indicates the maximum weight that each tire is able to support. Below is a quick rating of common Load Indexes:

Sidewall Markings

Here are some other markings you may find on your tire's sidewall:

• The M+S (also displayed as M&S or M-S) indicates the tire has all season capabilities. You will find this on almost all all season and winter tires. Summer tires will not have this designation. For a tire to get this designation, it must have a specified tread-to-void ratio, however it does not mean that the tire has passed any actual tests for it effectiveness in severe conditions.

• indicates a Severe Snow Conditions rating. Tires bearing this symbol will provide snow performance superior to tires only bearing the M+S symbol. These are the safest tires for any kind of winter driving. Some ski resorts will not even let you up their mountain if you do not have this symbol on your tires.

• DOT stands for Department of Transportation. The 10, 11 or 12 digit code appearing after the DOT designation gives information such as the week and year the tire was produced, as well as the manufacturer, plant, tire line, and size. The first 2 characters designate the tire's manufacturer and plant code. The third, fourth and fifth characters, are the tire size code. The last three or four numbers (4 numbers for years after 2000) are when the tire was manufactured. The first two digits of the date code represent the week and the last 1 or 2 digits represent the year.

• Maximum Inflation Pressure is the highest inflation pressure that the tire can withstand. This is not, however, the recommended inflation pressure. Inflation pressures should never be below the recommended pressure or above the maximum pressure branded on the sidewall. Also see Air Pressure.

Sidewall Descriptions

Below is a quick legend to notations describing the appearance of the tire's sidewall.

Uniform Tire Quality Grading

The Uniform Tire Quality Grading rating is a quality rating system developed by the American Department of Transportation. It is designed to tell consumers the relative performance of passenger tires (but does not apply to winter tires).

Below is an example of a UTQG Rating:

150A B

The "150" indicates the treadwear rating
the "A" indicates traction
the "B" indicates temperature

The Treadwear rating is based on a wear test performed on a 400 mile government test course covering specified sections of public roads in Texas. A group of not more than 4 test vehicles travels the course in a convoy so that all tires experience the same conditions. Tread groove depths of the tires being tested are measured after each 800 miles. The same procedure is followed for a set of "control" or "course monitoring tires" Upon the completion of the 7200 mile test, the rating results of both tires are compared, and the tires being tested are assigned a treadwear rating according to government standards. This number can be used to compare between tires. In the above example, this tire rated 150 should last 1/2 as long as a tire rated 300. The relative performance of tires depends upon the actual conditions of their use and may be significantly different from the norm due to differences in road characteristics and climate.

The Traction ratings are AA, A, B, and C, from highest to lowest. This measurement indicates a tires ability to stop in a straight line on wet pavement. The rating is based on a 40mph test where the brakes are "locked up" on wet asphalt and wet concrete surfaces. It's important to remember that this rating does not indicate the tires ability to resists hydroplaning, and do not apply to cornering traction.

Temperature ratings are determined by running tires on an indoor roadwheel test under specified conditions. Successive 30 minute runs are made in 5mph increments starting at 75mph and continuing until the tires fails. Tires with an A rating must withstand at least 114mph, B at least 99mph, and C at least 85mph. These measurements indicate the tire's ability to sustain high temperatures which often cause tires to wear away quickly or in extreme conditions lead to sudden tire failure.

Mixing Tires

Generally tires should not be mixed on any vehicle. To receive maximum safety and performance it is preferable to keep every tire on a vehicle identical in size, brand, model, rating etc. One of the only exceptions is if the front and rear wheels are different like on all Porsche's and other high performance vehicles.

Tire Storage

Storing Winter Tires
The best place to store winter tires is in a cool, dry location. (Basement, or possibly a garage). You can lay them down flat, stacked on top of each other no taller than 4 high. This offers the most support and should eliminate any fitting problems the following fall. We also recommend that you return to the store/dealer from where you purchased your tires from and ask for storage bags. This will protect the tires from natural ozone in the air which can cause tire rubber to dry and crack. Wrap each tire individually and stack them. Stored tires should be kept away from electric motors or welders as these produce ozone which will damage the rubber over time.

Air Pressure

The most common way of damaging tires is improper inflation. As tires lose pressure over time it causes them to experience irregular treadwear, poor vehicle handling and traction, and decreased gas mileage. Under inflated tires can build up excessive heat and blow out without warning. Pressure should be checked at least once a month using a good quality tire pressure gauge. Pressure should be checked when the tires are cold (tires have not been driven for 2 hours). You can find out what the proper inflation numbers on your tires are by checking the owner's manual of your vehicle. Even if the tires have been changed since the vehicle was new, the car manufacturers recommended pressures still apply.  Also remember to check your spare tire for loss of air.

Tread Wear Indicator

As your tires wear down, their ability to grip the road decreases. Each tire has what are known as wear bars. These appear at various points around the tire as bars running through the tread design from one side of the tire to the other. When your tires are legally worn out (2/32") the tread will be at the same level as the tread wear indicators and they will be easily visible. Usually before the tire gets to this point, they will begin to feel unsafe. If that is the case, do not wait for them to get to the wear bars. Just because the tread depth is not as low as the tread wear bar, does not mean it is safe.

Tire Rotation

Because each tire on your car typically supports a different amount of weight, and your driving patterns will typically wear out one tire faster than the others, it's important to rotate your tires every 5000 to 8000 miles. Rotation patterns differ depending on what kind of vehicle you drive. The best place to check is in your vehicle's owners manual. If you can not find what you are looking for, below are some diagrams sowing you the most common patterns.

Of course, if your vehicle has different sizes of tires from front to back, or if your tires are directional, these may not work. Consult a professional if you are still not sure.

Alignment

Vehicle alignment is one of the most important factors in not only vehicle care, but tire care. Improper alignment on either the front or rear wheels can result in unusual tread wear, damage to your suspension, and unusual handling for the car. Wheel alignments should be performed every time you install a new set of tires, and any time you experience an impact such as a large pot hole, curb, or other obstacle. For maintenance purposes, alignment should be checked every 30,000 km (about 18,700 miles).

There are several alignment types, including both two and four wheel alignment. Four wheel alignment is always recommended, but some vehicles are not able to have the rear alignment adjusted. Consult with an alignment specialist you trust to find out what's best for your car.

Warning signs that you might need an alignment are your car pulling to one side or another, and irregular tire wear.

Puncture Repairs

A puncture to any area of a tire's tread will affect performance and safety, and therefore must be immediately attended to through either replacement of the tire (spare or new tire) or a patch. Any patch that is applied to a tire must be applied to both the outer part of the tire (tread) and the inner part of the tire. The reason for this is that the rubber on each side is very different (inside is made of halobutyl rubber meant for holding air, while the outside is a harder durable rubber primarily designed for traction). A good tire repair can only be made if the tire is removed from the rim (wheel) and inspected carefully for any hidden damage. Only straight through holes, 3/16" or smaller diameter may be repaired, when no secondary damage has ocured.

Noise and Vibration Problems

Below are the most common (but not the only) causes of noise and vibration problems:

• Tire / wheel assembly is out of balance

• No hub rings on aftermarket wheels

• Incorrect mounting hardware for aftermarket wheels

• Tire is poorly seated on the rim

• Irregular tire wear

• Out of round rim

• Out of round tire

Do not ignore apparent impacts, pulling, or vibration. This could be an indicator of tire damage as much as mechanical problems that should be inspected by a professional. If there is a problem with your tires and the way they have been installed they will most likely begin to shake and vibrate your vehicle at between 50 and 65 mph.

When do you need to Replace Tires?

Tires are typically replaced when their natural lifespan has come to an end. There are however any number of factors that can affect this including storage, temperature, surfaces they are driven on, how aggressive of a driver you are, punctures, etc.

The usual recommendation for replacing tires is when they no longer feel safe to the driver. You can see when they are legally worn out using the tread wear indicator. A typical set of tires under normal driving conditions will last approximately 40 000 miles or 64 000 km. Some tires of-course are designed for much longer, even up to 80 000 miles or 128 000 kilometers.

Mounting and Balancing

When mounting wheels & tires on to the vehicle, ensure the following checks are made:

• Wheels are not damaged in any way

• There is no dirt or oily build up between the hub and the wheel

• Lugs are properly torqued

• Both tire beads are securely mounted

•  Any retaining clips on the brake drums are removed

Tires are manufactured to close tolerances, however as they wear their mass can become unevenly distributed, negatively effecting the original balance. The most common signs of unbalanced tires are vibration problems. These can affect the speed, handling and mileage of your vehicle. Balancing is done by a computer that spins the wheel / tire assembly, senses heavy spots, and gives a location for the technician to apply weight to counter the heavy spots. The best type of balance is a dynamic balance, and this should be performed whenever possible. (Some rim designs will not allow this type of balance and you would have to settle for a static balance)