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Glossary
| Tire identification diagram | Tire identification diagram, light truck specific features |
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Contents
- Aspect Ratio (series)
- Belt
- Bolt Circle
- Camber
- Cold Inflation Pressure
- Construction Type
- Cords / Piles
- Cross Section
- Drop Center Rims
- Flange
- Hub-Centric Wheel
- Hydroplaning
- Innerliner
- Load Index
- Load Range / Ply rate
- Lug-Centric Wheel
- Overall Tire Diameter
- Radial Ply tire
- Revolutions Per Mile (RPM)
- Rim Diameter
- Rim Width
- Section Width
- Service Description
- Sidewalls
- Static Loaded Radius
- Stud Size
- Tire Size
- Toe
- Tread
- Tread Depth
- UTQG
Aspect Ratio (Series)
The hieght of a tire’s sidewall in relation to its tread width. For example, a ’60 series tire indicates that the sidewall is 60 percent as high as the tread is wide.
Belt
One or more layers of material that surround the body plies. The belts run parallel with the beads and reinforce the area directly beneath the tread.
Bolt Circle
Refers to the diameter of an imaginary ring drawn through the center of the wheel studs or mounting holes.
Camber
An alignment angle that refers to the tilt of the tire from vertical as viewed from the front of the vehicle.
Cold Inflation Pressure
The air pressure of a tire that has been driven less than 1 mile or has been idle for at least 3 hours.
Construction Type
Bias tire (or cross ply) construction utilizes body ply cords that extend diagonally from bead to bead, usually at angles in the range of 30 to 40 degrees, with successive plies laid at opposing angles forming a crisscross pattern to which the tread is applied. The design allows the entire tire body to flex easily, providing the main advantage of this construction, a smooth ride on rough surfaces. This cushioning characteristic also causes the major disadvantages of a bias tire: increased rolling resistance and less control and traction at higher speeds.
Belted bias tire starts with two or more bias-plies to which stabilizer belts are bonded directly beneath the tread. This construction provides smoother ride that is similar to the bias tire, while lessening rolling resistance because the belts increase tread stiffness. However the plies and belts are at different angles, which lessens performance compared to radial tires.
Radial tire construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approximately right angles to the centerline of the tread, and parallel to each other, as well as stiff stabilizer belts directly beneath the tread. The advantages of this construction include longer tread life, better steering control, and lower rolling resistance. Disadvantages of the radial tire include a harder ride at low speeds on rough roads and in the context of off-roading, decreased "self-cleaning" ability and lower grip ability at low speeds.
Cords or Plies
Layers of rubber-impregnated material within the casing, such as polyester or steel.
Cross Section
Drop Center
The area of the rim with the smallest inner diameter. They are designed for passenger, light truck and tubeless truck and bus tires.
Flange
The outmost lip of the rim where balancing weights are usually attached.
Bead flange
Hub-Centric Wheel
A wheel with a machined center hole that fits precisely over the raised portion of the wheel hub/ or axle flange.
Hydroplaning
A condition in which the tires lose contact with the road due to the inability of the tread to channel water away for the tire.
Innerliner
A rubber-butyl material applied to the inside of the casing during the manufacturing process. The innerliner keeps the casing airtight.
Load Index
The load index on a passenger car tire is a numerical code stipulating the maximum load (mass, or weight) each tire can carry. For Load Range "B" tires, ETRTO standards specify the load index rating at an inflation pressure of 36 psi while TRA standards measure the load capacity at an inflation pressure of 35 psi. The two standards vary slightly with the capacity required for different inflation pressures.
| Code | Pounds | Kilograms | Code | Pounds | Kilograms | Code | Pounds | Kilograms | ||
|---|---|---|---|---|---|---|---|---|---|---|
| 60 | 551 | 250 | 82 | 1,047 | 475 | 104 | 1,984 | 900 | ||
| 61 | 567 | 257 | 83 | 1,074 | 487 | 105 | 2,039 | 925 | ||
| 62 | 584 | 265 | 84 | 1,102 | 500 | 106 | 2,094 | 950 | ||
| 63 | 600 | 272 | 85 | 1,135 | 515 | 107 | 2,149 | 975 | ||
| 64 | 617 | 280 | 86 | 1,168 | 530 | 108 | 2,205 | 1,000 | ||
| 65 | 640 | 290 | 87 | 1,201 | 545 | 109 | 2,271 | 1,030 | ||
| 66 | 661 | 300 | 88 | 1,235 | 560 | 110 | 2,337 | 1,060 | ||
| 67 | 677 | 307 | 89 | 1,279 | 580 | 111 | 2,403 | 1,090 | ||
| 68 | 695 | 315 | 90 | 1,323 | 600 | 112 | 2,470 | 1,120 | ||
| 69 | 717 | 325 | 91 | 1,356 | 615 | 113 | 2,536 | 1,150 | ||
| 70 | 738 | 335 | 92 | 1,389 | 630 | 114 | 2,601 | 1,180 | ||
| 71 | 761 | 345 | 93 | 1,433 | 650 | 115 | 2,679 | 1,215 | ||
| 72 | 783 | 355 | 94 | 1,477 | 670 | 116 | 2,756 | 1,250 | ||
| 73 | 805 | 365 | 95 | 1,521 | 690 | 117 | 2,833 | 1,285 | ||
| 74 | 827 | 375 | 96 | 1,565 | 710 | 118 | 2,910 | 1,320 | ||
| 75 | 853 | 387 | 97 | 1,609 | 730 | 119 | 2,999 | 1,360 | ||
| 76 | 882 | 400 | 98 | 1,653 | 750 | 120 | 3,087 | 1,400 | ||
| 77 | 908 | 412 | 99 | 1,709 | 775 | 121 | 3,197 | 1,450 | ||
| 78 | 937 | 425 | 100 | 1,764 | 800 | 122 | 3,306 | 1,500 | ||
| 79 | 963 | 437 | 101 | 1,819 | 825 | 123 | 3,418 | 1,550 | ||
| 80 | 992 | 450 | 102 | 1,874 | 850 | 124 | 3,528 | 1,600 | ||
| 81 | 1,019 | 462 | 103 | 1,929 | 875 | 125 | 3,638 | 1,650 |
E.T.R.T.O. 1991 - Section 13
Load Range / Ply Rate
Load range on light truck tires indicates ply rating and load pressure (PSI). Tire pressure is also measured in kilopascals or bars. One psi is equal to 6.895 kPa. 100 kilopascals is equivalent to one bar. Therefore, 300 kPa is equivalent to 44 psi.
| Load Range | Ply Rating | Load Pressure (PSI) |
|---|---|---|
| B | 4 | 35 |
| C | 6 | 50 |
| D | 8 | 65 |
| E | 10 | 80 |
| F | 12 | 95 |
Lug-Centric Wheel
A wheel with a large center hole surrounded by elongated mounted holes. Wheel-to-hub centricity is achieved using specially designed lugs.
Overall Tire Diameter
The diameter of an unloaded, inflated tire measured from the crown on one side to the crown on the opposite side. The free radius equals one-half the overall diameter. Sometimes called the outside diameter.
Overall tire diameter must be calculated, since it isn't explicitly in the tire size - a 195/60-14 standard XR4 tire is 195mm wide and has a sidewall height of 60% of 195 = 117mm, or, when divided by 25.4 mm/in., 4.606 inches. Multiply this by 2 and add to the 14" wheel diameter and you get an overall diameter of 23.213 inches. For 17 inch wheels that means you need a sidewall height of (23.213 - 17) / 2 = 3.106 inches or 79 mm. You can have a mm or two slack either way with a minor speedometer error, so for instance 205/40-17's would work since 40% of 205 is ~80. If you have Microsoft Excel or some other spreadsheet package, it's really easy to whip up a quick little chart to figure suitable tire sizes and speedometer errors.
Radial Ply Tire
A tire in which the plies run perpendicular (90-degrees) to the beads
Revolutions Per Mile (RPM)
The measured number of revolutions made by a tire traveling one mile.
Rim Diameter
The diameter of the rim bead seats that support a tire, normally indicated in whole numbers in inches for passenger cars
Rim Width
The distance between rim flanges.
Section Width
The section width of a tire is the measurement of the width of the tire tread from sidewall to sidewall.
Example: 195/65R15, the section width is 195, the nominal width of the tire is approximately 195mm at the widest point.
Service Description
The code is made up of one or two letters, or one letter and one number. It indicates the maximum permitted speed that the tire can sustain for a ten minute endurance without being in danger.
| Code | MPH | KM/h | Code | MPH | KM/h | |
|---|---|---|---|---|---|---|
| A1 | 3 | 5 | L | 75 | 120 | |
| A2 | 6 | 10 | M | 81 | 130 | |
| A3 | 9 | 15 | N | 87 | 140 | |
| A4 | 12 | 20 | P | 94 | 150 | |
| A5 | 16 | 25 | Q | 100 | 160 | |
| A6 | 19 | 30 | R | 106 | 170 | |
| A7 | 22 | 35 | S | 112 | 180 | |
| A8 | 25 | 40 | T | 118 | 190 | |
| B | 31 | 50 | U | 124 | 200 | |
| C | 37 | 60 | H | 130 | 210 | |
| D | 40 | 65 | V | 149 | 240 | |
| E | 43 | 70 | Z | OVER 149 | OVER 240 | |
| F | 50 | 80 | W | 168 | 270 | |
| G | 56 | 90 | (W) | OVER 168 | OVER 270 | |
| J | 62 | 100 | Y | 186 | 300 | |
| K | 68 | 110 | (Y) | OVER 186 | OVER 300 |
Sidewalls
flex area between the beads and tread.
Static Loaded Radius
The static loaded radius is the distance from the center of the axle to the contact surface when prescribed load is applied to a tire mounted on the measuring rim width and inflated to the recommended pressure.
Stud Size
 | ||||
| #12 | #13 | #15 | #16 | #17 |
| Stud Number | Hole Depth | Housing Color |
|---|---|---|
| #12 | 12/32" | Silver |
| #13 | 13/32" | Gold |
| #15 | 15/32" | Blue |
| #16 | 16/32" | Silver |
| #17 | 17/32" | Gold |
Tire Size
Automobile tires are described by an alphanumeric code, which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of its key limitations, such as load-bearing ability, and maximum speed. Sometimes the inner sidewall contains information not included on the outer sidewall, and vice versa.
The code has grown in complexity over the years, as is evident from the mix of metric and imperial units, and ad-hoc extensions to lettering and numbering schemes. New automotive tires frequently have ratings for traction, treadwear, and temperature resistance (collectively known as The Uniform Tire Quality Grade (UTQG) ratings).
Example: P205/60R15 or 7.50R15LT or 31x10.50R15
Toe
An alignment angle that refers to the position of the tires in relation to the vehicle’s centerline.
Tread
The part of the tire that provides the contact area. The tread is made from a variety of natural and synthetic rubber compounds.
Tread Depth
The depth of tread on the tire.
UTQG
Stands for Uniform Tire Quality Grading.
The UTQG rating is made up of three components:
Treadwear
The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would wear twice as long on the government test course under specified test conditions as one graded 100. It is an oversimplification to assume treadwear grades will be proportional directly to your actual tire mileage. The relative performance of tires depends upon the actual conditions of their use and may vary due to driving habits, service practices, differences in road characteristics and climate.
Traction
Traction grades, from highest to lowest, are AA, A, B and C. They represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The testing does not take into account cornering, hydroplaning or acceleration.
Temperature
The temperature grades, from highest to lowest, are A, B and C. These represent the tire's resistance to the generation of heat.