Tire Tread - The flat area of the tire that contacts the road surface. A tire's tread construction determines the adhesion characteristics of the tire in all driving conditions.
Tire Bead - The narrow band that anchors the tire to the rim and maintains a leak-free seal. This area transmits acceleration, turning, braking and all other forces between the vehicle and the road.
Tire Sidewall - The vertical portion of the tire that extends from the road surface to the bead. Sidewall construction and depth affects the ride and handling of the tire. A narrow, stiff sidewall offers more responsive steering, but a deep, supple sidewall will flex to provide a smoother ride.
Tire Shoulder - The curved region where the vertical sidewall of the tire meets the horizontal tread.
Tire Sidewall Information
On the sidewall of every tire, there's a great deal of information that identifies its construction and capabilities.
Example: P185/75R14 82S
P
Service type: Indicates this is a passenger vehicle tire, as opposed to a tire made for a light truck (LT) or other vehicle.
185
Section Width: The width of the tire in millimetres from sidewall to sidewall. This measurement varies depending on the width of the rim to which the tire is fitted: larger on a wider rim, smaller on a narrow rim. The number on the side of the tire indicates the width measured with the tire fitted to the recommended rim width.
75
Aspect Ratio: The ratio of height to width. This tire's height is 75% of its width.
R
Internal Construction: How the plies are constructed in the tire carcass. "R" means radial. "B" in place of the "R" means the tire is belted bias construction. "D" in place of the "R" means diagonal bias construction.
14
Rim Diameter: The diameter of the wheel in inches.
82
Load Index: This tire has an industry-standard maximum load of 475 kg (1,047 lbs.) Different load index numbers correspond to different maximum loads. The maximum load is shown in lbs. (pounds) and in kg (kilograms), and maximum pressure in PSI (pounds per square inch) and in kPa (kilopascals).
S
Speed Rating: This tire has an industry-standard maximum service speed of 130 mph. Different letters correspond to different maximum service speeds.
Here are some other markings to look for on your tire's sidewall:
The mountain/snowflake symbol indicates a Severe Snow Conditions rating—the safest tires for any kind of winter driving. These tires have been designed specifically for use in cold weather and severe snow conditions, and have been performance tested as meeting or exceeding industry established snow traction performance requirements. See our Winter Tires Guide for complete details.
The M+S (also displayed as M&S or M-S) indicates the tire has all-season capabilities. Tires bearing this mark offer great traction and can be used in rain, snow, and muddy conditions. This designation indicates a specified tread-to-void ratio; however it does not mean that the tire has passed any road tests ensuring effectiveness in severe winter conditions.
All the winter tires sold at Canadian Tire will accept winter studs. Note that there are different provincial rules and regulations for the use of studded tires.
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 pressure recommended by your vehicle manufacturer or above the maximum pressure branded on the tire's sidewall.
Branding on the sidewall of tires lists the materials and number of layers of each material used to reinforce the rubber. Here's an example of how a typical tire's basic construction materials are usually presented:
TREAD 2 POLYESTER + 2 STEEL + 1 NYLON
SIDEWALL 2 POLYESTER
In this example, the branding indicates that moulded into the rubber under the centerline of the tread lies:
two radial body plies of polyester cord
two belts of angled steel cord
one circumferential cap ply of nylon cord.
It also identifies that in each sidewall lies two radial body plies of polyester cord (a continuation of the same two radial body plies that were listed under the centerline of the tread).
Some construction information may not be indicated in the branding for tires.
Many high-speed tires are constructed with circumferential reinforcements above the steel belts. These belt edge strips or full cap plies are not under the centerline of the tread, so this information won't be indicated in the branding for the tread area.
Ultra high performance tires may also use fabric or steel cord reinforced sidewalls to increase steering response and cornering stability. However, since this sidewall-reinforcing material is not present at the widest points of the tire's sidewalls, this information won't be indicated in the branding for the sidewall area.
Tire Sidewall Descriptions
In addition to the construction branding and ratings, tire sidewalls can include stripes, bands or lettering that give a tire a distinctive look. Below is a quick legend of notations used for describing the appearance of a tire's sidewall.
The tire size branded on the sidewall provides a significant amount of information about the tire's intended purpose, dimensions, load capacity and high temperature/high speed durability.
Our primary example will be based on variations of P185/75R14 82S, although other sizes will appear where appropriate.
Service Type
Most tire sizes begin with one or two letters that identify the type of vehicle or type of service they were designed for. Here are some of the most common indicators:
P185/75R14 82S
P = Tire sizes that begin with a P indicate the tire is a P-metric size. These tires are designed for passenger vehicles such as cars, minivans, SUVs and light duty pickup trucks.
185/75R14 82S
If there isn't a letter preceding the three-digit numeric portion of a tire size, it signifies the tire is a Euro-Metric size, sometimes just referred to as Metric. Euro-metric sizes are dimensionally equivalent to P-metric sizes, but can subtly differ in load carrying capabilities.
LT245/75R16 108/104S
LT = Tire sizes beginning with LT indicate Light Truck-metric size tires designed for use on vehicles capable of carrying heavy cargo or towing large trailers. This includes medium and heavy-duty pickup trucks, SUVs and full-size vans.
7.50R16LT 112/107Q
8.75R16.5LT 104/100Q
31x10.50R15LT 109Q
LT = If a tire size ends with LT, it indicates the tire is either an earlier Numeric, Wide Base or Flotation Light Truck size. Numeric sizes are designed for use on vehicles that are capable of carrying heavy cargo and towing trailers. Wide Base sizes use 16.5-inch diameter rims. Flotation sizes are wider, oversized tires designed to help the vehicle drive on top of loose dirt or sandy surfaces.
Section Width
The three-digit numeric portion following the service type designation identifies the tire's Section Width (cross section) in millimetres.
P185/75R14 82S
This tire is 185 millimetres across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel.
You can convert the section width measurement to inches by dividing the measurement by 25.4.
185 mm / 25.4 = 7.28"
Tire Sidewall Aspect Ratio
Typically following the three digits identifying the tire's Section Width is a two-digit number that identifies the tire's aspect ratio or profile. A lower profile tire will have a shallower sidewall, providing enhanced handling and responsiveness.
P185/75R14 82S
The 75 indicates that this tire size's sidewall height (from rim to tread) is 75% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall.
We know that this tire size's section width is 185 mm and that its section height is 75% of 185 mm. By converting the 185 mm to inches (185 / 25.4 = 7.28") and multiplying it by 75% (.75) we can determine that tire section height is 5.46".
Internal Construction
Following the two digits to indicate aspect ratio, a letter is used to identify the tire's internal construction.
P185/75R14 82S
The R size identifies that the tire has a Radial construction, in which the tire's body plies "radiate" out from the imaginary center of the wheel. Radial tires are by far the most popular type of tire today representing over 98% of all tires sold.
If there was a B in place of the R (P185/75B14), it would indicate the tire features belted bias construction.
If the R in the size was replaced with a D (P185/75D14), it would identify that the internal tire body plies crisscross on a Diagonal and that the tire has a "bias ply" construction. Tires using this construction are used for light truck and spare tire applications.
Diameter of Wheels and Tires
Following the internal construction, a number indicates the bead of the tire, and the required wheel size.
P185/75R14 82S
The 14 indicates the tire is designed to be installed on 14 inch diameter rims.
Most commonly, tires express the rim diameter in whole inches ranging from 8 to 28. While not as common, two additional "unique" types of tire/wheel diameters are still in use today.
Some heavy-duty trailers, heavy-duty light trucks and box vans have a tire and wheel rim diameter expressed in "half" inches (8.00R16.5LT, as well as, 14.5, 15.5, 17.5 and 19.5).
Some integrated wheel/tire systems are in use on a very limited basis as Original Equipment in North America. These systems feature "asymmetric" beads in which the outside bead and inside bead are actually different diameters.
Wheels and tires with unique rim diameters should never be combined with traditional "inch rim" wheels and tires. These unique tire/wheel diameters feature bead profiles that have a different shape than traditional "inch rim" sizes, and were developed specifically because their application required them to be different than conventional wheels and tires.
Always confirm tire and wheel diameters match before mounting the tire on the wheel.
Load Index & Tire Speed Ratings
Following the tire and wheel diameter, two numbers and a letter indicate the Load Index and Tire Speed Ratings, also known as its Service Description.
P185/75R14 82S
82 indicates the Load Index and S indicates the Speed Rating.
Load Index
P185/75R14 82S - The load index (82 in this example) indicates the tire's relative load carrying capabilities. The numbers correspond to a set index, with higher numbers indicating the ability to carry a heavier load. Our example, 82, indicates the tire can carry about 475 kg (1,047 lbs.)
Typical load indexes for tires used on passenger cars and light trucks range from 70 to 110.
Load Index
Pounds
Kilograms
Load Index
Pounds
Kilograms
71
761
345
91
1,356
615
72
783
355
92
1,389
630
73
805
365
93
1,433
650
74
827
375
94
1,477
670
75
853
387
95
1,521
690
76
882
400
96
1,565
710
77
908
412
97
1,609
730
78
937
425
98
1,653
750
79
963
437
99
1,709
775
80
992
450
100
1,764
800
81
1,019
462
101
1,819
825
82
1,047
475
102
1,874
850
83
1,074
487
103
1,929
875
84
1,102
500
104
1,984
900
85
1,135
515
105
2,039
925
86
1,168
530
106
2,094
950
87
1,201
545
107
2,149
975
88
1,235
560
108
2,205
1,000
89
1,279
580
109
2,271
1,030
90
1,323
600
110
2,337
1,060
Tire Speed Rating
P185/75R14 82S - The speed rating (S in this example) indicates the maximum service speed of which the tire is capable. The letter corresponds to a set index; with a few exceptions (ex.: H, Z) letters which appear later in the alphabet indicate the ability to travel at a higher speed. Our example, S, indicates the tire can safely operate at speeds of up to 180 km/h (112 mph)
Tires are engineered to withstand a maximum load and inflation pressure. These maximums for tires are branded on the sidewall of all tires sold in North America. Passenger vehicles specify the load ranges while light trucks use letter-indicated load ranges that ascend in alphabetical order.
Prior to using load ranges, ply ratings were used, indicating the relative strength of tires by identifying the actual number of plies used in the tire's construction. Because tire construction has changed over the years, load ratings were developed to indicate the equivalent strength as compared to early bias ply tires.
In our example of the P185/75R14 82S tire, its maximum load and maximum tire inflation pressure typically presented on the sidewall as follows:
MAX. LOAD 2000 kg (4410 lbs)
AT 760 kPs (110 psi) COLD
This branding identifies that the tire in this example must be capable of, and be rated to carry 2000 kg (4,410 pounds), and that the maximum tire inflation pressure for this tire is 300 kPa (44 psi).
Tire pressures are most commonly measured in psi—pounds per square inch, Kilopascals (kPa) or bars of pressure (bars).
1 psi = 6.895 kPa = 0.0689 bars
The maximum load rating for the tire is based on industry standard tire load pressures—not the maximum tire pressure specific for the tire.
Load range information for passenger tires
Sizing System
Tire Load Range
Abbreviation
Example
Load Pressure
P-metric
Light Load
LL
P185/75R14
35 psi
Standard Load
Nothing or
SL
P185/75R14
P185/75R14 SL
35 psi
Extra Load
XL
P185/75R14 XL
41 psi
Euro-metric
Standard
Nothing or
SL
185/75R14
185/75R14 SL
36 psi
Reinforced or Extra Load
RF or XL
185/75R14 RF
185/75R14 XL
42 psi
It's worth noting that Standard Load Range tires may not indicate a load range on the tire. It's also important to note the optimal tire pressure for your vehicle is determined by the vehicle itself, not by the tires. To determine the recommended tire pressure for your vehicle, consult the tire information placard (usually found on the driver's door or doorjamb) or your owner's manual.
Light truck tires and trailer tires are branded with their load range (Load Range E or LRE) or their ply rating (10 Ply Rated) on their sidewalls and also list their appropriate load range letter in their descriptions.
Tire size type
Tire Load Range
Ply Rating
Description Example
Load Pressure
Light Truck
(indicated on sidewall with LT)
B
4
LT185/75R14 B
35 psi
C
6
LT185/75R14 C
50 psi
D
8
LT185/75R14 D
65 psi
E
10
LT185/75R14 E
80 psi
F
12
LT185/75R14 F
95 psi
ST-metric special sized trailer tires
(example only)
D
8
ST185/75R14 D
65 psi
When changing tire sizes or converting from one type of size to another, it is important to confirm that the new tire’s rated load capacity is sufficient to carry the vehicle's Gross Axle Weight Ratings—one way to do this is to ensure the Load Index of the new tire is equal to or greater than the Load Index of your original tire.
About Tire Tread
Tire Tread Patterns
Tire tread design consists of the blocks, ribs, grooves, and thin snipes molded into the tire. These designs incorporate features to fine-tune noise, direct moisture, and provide all-important traction for your vehicle. Several basic designs help meet the conditions you'll face on the road.
Symmetric Tread Patterns feature the same tread blocks across the entire tread face, and allow multiple tire rotation patterns.
Asymmetric Tread Patterns change across the face of the tire, and are designed to blend the surface contact needs for dry grip and tire tread depth required water dispersal or snow traction. The outboard side of the tire may feature larger tread blocks for stability and cornering on dry roads while the inboard side may feature smaller independent tread blocks to channel moisture or to aid traction in winter while driving straight ahead. These tread patterns allow using multiple tire rotation patterns.
Directional (Unidirectional) Tread Patterns are designed to roll in only one direction. The lateral grooves with v-shaped tread blocks pump water more efficiently through the tread pattern to enhance hydroplaning resistance at high speeds. Directional tires are to be used on only one side of the vehicle and are intended to be rotated from the front axle to the rear axle.
Tire Tread Markings
When you buy tires, you may notice on a new set of tires that the tread itself has several lines numbers and letters. These codes are left over from the tire production process.
At once stage of tire production, the tread compound is prepared by extruding or squeezing warm rubber into a metal die to create a slab of tread compound cut to the precise circumference of the tire. Thousands of these slabs are produced every day, so the slabs are often marked and coded prior to molding, to indicate the specific tire model and production lot. These slabs are then applied to the tire and molded. The coding can still be seen on the surface after molding, with some of the coding squeezed all the way down to the bottom of the tread grooves.
When developing tires, vehicle manufacturers will ensure the tires they use provide what they feel is the best driving and handling experience for their vehicles.
Tires contribute enormously to the feel of a vehicle—its ride, handling and performance. Vehicle manufacturers understand this, and so select tires which will provide a smooth ride, responsive handling, or sporty performance, depending on the driving profile they are creating for their vehicles.
Manufacturers must play a balancing act in an effort to determine the ideal blend of features and performance to provide optimal results on the road. The OE tires for fuel efficient vehicles will be engineered for increased efficiency while OE tires for sports vehicles will focus on handling and performance.
While technology continues to increase capabilities on all these facets, the "best" tires will always be a compromise. This is because one set of attributes can be directly opposed to another set of attributes. For example, a tread that increases traction will reduce rolling resistance and efficiency. A stiff sidewall that improves handling responsiveness will reduce the smoothness of ride.
Tire Ratings and Comparisons:
Uniform Tire Quality Grading (UTQG)
Uniform Tire Quality Grade (UTQG) standards were developed to equip consumers with information to compare tires based on relative treadwear, traction and temperature capabilities. These gradings are used mostly for all season tires for passenger vehicles. They are not required for deep treaded light truck tires, winter tires, temporary spare tires, and other select tires.
The UTQG ratings are assigned by the tire manufacturers based on their test results or those conducted by an independent testing company they have hired.
Treadwear Grades
UTQG Treadwear Grades are based on actual road use, comparing the test tire's performance to the performance of standardized monitoring tires over a 7,200 mile (11 600 km) course. The tires are compared at the end of the course, and the grade indicates how long the test tire will last in comparison to the test tire. For example, a grade of 200 would indicate the test tire would last twice as long as the monitoring tire.
UTQG Treadwear Grades are open to some interpretation on the part of the tire manufacturer. The grades are assigned after only a short period of treadwear. When the raw data is extrapolated, results may differ depending on how optimistic the calculations are. While comparing the Treadwear Grades of tire lines within a single brand may be helpful, the figures may not be as useful for comparing across different brands.
Traction Grades
UTQG Traction Grades are based on the tire's straight line wet coefficient of traction as the tire skids across a test surface. The UTQG traction test does not evaluate dry braking, dry cornering, wet cornering, or high speed hydroplaning resistance. Test tires are installed on an instrumented axle of a "skid trailer" which is pulled behind a truck at a constant 40 mph (65 km/h) over wet asphalt and wet concrete test surfaces. The axle's brakes are momentarily locked and the axle sensors measure the tire's coefficient of friction (braking g forces) as it slides. Since this test evaluates a sliding tire at a constant speed, it places more emphasis on the tire's tread compound and less emphasis on its tread design.
In 1997, the UTQG Traction Grades were revised to provide a new category of AA for the highest performing tires in addition to the earlier A, B and C grades. Previously the A grade had been the highest available and was awarded to tires that offered wet coefficients of traction above 0.47 g on asphalt and 0.35 g on concrete. Today the grades and their traction coefficients are as follows:
Traction Grades
Asphalt g force
Concrete g force
AA
Above 0.54
0.41
A
Above 0.47
0.35
B
Above 0.38
0.26
C
Less Than 0.38
0.26
Temperature (Resistance) Grades
The UTQG Temperature Grade indicates the extent to which heat is generated or dissipated by a tire. The grade is established by measuring a loaded tire's ability to operate at high speeds without failure by running an inflated test tire against a large diameter high-speed laboratory test wheel.
Temperature Grades
Speeds in mph
A
Over 115
B
Between 100 to 115
C
Between 85 to 100
This laboratory test is similar to those used to confirm a tire's speed ratings, though the details do differ. Everytire sold in the United States must be capable of earning a "C" rating which indicates the ability to withstand 85 mph (137 km/h) speeds.
Your car will handle differently after installing new tires. When you buy car tires, take the time to get a feel for the change in your vehicle's traction and handling.
At the end of their use, your old tires will have much less tire depth than your new tires. This means the amount of tread surface in contact with the pavement was larger before buying new tires, resulting in greater responsiveness on dry roads, and poorer traction on wet roads. Depending on road conditions, your new tires may feel slower to respond, even if you had the same model of tires previously.
Tires are constructed from several layers of rubber, steel and fabric that require a break-in period before they reach maximum performance. To give these components time to fully integrate, for your first few hundred kilometres avoid any aggressive driving—stick with easy acceleration, cornering and braking.
New tires may also have a mold release lubricant on them as a residue from the production process. You should be aware your vehicle might initially have reduced traction before this thin layer is worn away from regular driving.
Tires & Fuel Economy
Tires can impact your vehicle's fuel efficiency in many ways. While some factors can increase fuel efficiency, other factors can actually result in less than accurate calculations.
Most vehicle manufacturers provide low rolling resistance tires as Original Equipment. Rolling resistance is the force required to maintain the forward motion of a tire in a straight line at a constant speed.
Rolling Resistance
Low rolling resistance tires feature reduced weight, thinner sidewalls, shallower treads and low rolling resistance designs and tread compounds, all of which increase the fuel efficiency of your vehicle. A high performance replacement radial tire could increase rolling resistance on a vehicle by as much as 20%.
It should be noted that rolling resistance only accounts for one facet of your vehicle's fuel efficiency. With city driving, tire rolling resistance accounts for about 15% of a vehicle's fuel efficiency, and with highway driving, this number is closer to 25%. So the impact of 20% more rolling resistance would be a drop in fuel economy of 3% in the city and 5% on the highway. This may not be significant enough to notice at the pumps, but over a longer time period such as a year, this difference may be enough to make the purchase of low rolling resistance tires a cost-saving measure.
The rolling resistance of your tires will also gradually drop over the tire's lifespan by about 20%, as tire tread depth becomes shallower and rubber hardens over time. While you are unlikely to notice the slow increase in fuel efficiency, you may notice the small decrease in efficiency with the sudden change from old to new tires.
You can reduce the rolling resistance of your tires by ensuring they are properly inflated. Under-inflated tires have increased rolling resistance and decreased fuel economy.
Tire Diameter and Wear
You may find this interesting to consider: your calculation of fuel efficiency can be thrown off by the subtle difference in tire circumference between new and old tires. A vehicle's odometer works by measuring the number of revolutions of your car's tires, so a tire with worn tread will give a slightly higher odometer reading than a new tire, because the diameter of the worn tire will be slightly smaller. Since fuel economy is calculated by the amount of fuel used to travel a set distance, the shorter distance reading given by new tires will make the fuel economy slightly worse than it actually is.
Tires identified as the same size may vary in actual size, depending on the manufacturer. This small variation, much like the difference between worn and new tires, can be enough to appear to reduce fuel economy.
These small differences are enough to significantly change the results of your calculations.
Tire Storage
Properly storing your tires between seasons can make a big difference in the life of your tires. Following a few simple tips will make winter tire storage easier, and will protect your investment. Plus remember, your tire quality directly affects your safety. Store your tires properly, and save the cost and inconvenience of replacing your tires sooner due to unnecessary wear or damage.
Before You Store
Clean your tires well to remove road grime, brake dust and any debris before storing them. Be sure tires are thoroughly dry before placing them into storage.
To protect your tires from dust and dirt while they're in storage, use seasonal tire covers. These include an integrated handle to make tires easy to move around. Sporty tire covers offer a contour fit to keep your garage looking tidy and are sized to fit most tires from 13” to 29”, including summer tires, winter tires, some off-road tires, trailer tires, spare tires, and vintage and limited edition tires.
Tire covers can be used with tires still affixed to the rims, and will prevent white walls or tire lettering from becoming scuffed or damaged. They can be re-used multiple times unlike the covers given to you at your local shop, and are easily transferred between your tires when changing them for the seasons.
How To Store
If storing your tires without rims, they should be stored upright and rotated every month to avoid flat spots from developing. A tire rack will help you keep your tires upright and in place.
If you are storing tires with rims, it's best to store them horizontally, rotating every month. A tire stand is an ideal solution. When storing inflated tires, be sure to deflate tires to 50% of suggested pressure and then re-inflate prior to remounting the tires in order to prevent the rubber from becoming stretched and split.
Where To Store
When storing your tires, keep them in a cool, dark, well-ventilated area. Be sure to protect your tires from elements that can degrade the rubber:
Sunlight
Solvents, fuels, lubricants and other chemicals
Ozone emitters (i.e. electric motors, welders)
Heat sources (i.e. heaters)
After storage and before re-installing your tires, be sure to examine the tires for any damage, and check tire interiors to ensure there is no dirt, debris or water accumulation.
