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A-Z Glossary Terms Used For Wheel and Tire.(Also Download These File In PDF)



A

Air Pressure :-
The amount of air inside the tyre, measured in either pounds per square inch (psi) or bars. The correct pressure for tyres can usually be found in the vehicle handbook and often on the flap to your petrol tank.

Asymmetric Tread :-
Tires with an asymmetric tread have a continuously unique design across the width of the tread. The pattern elements oriented towards the outside of the tire are focused more on handling and dry traction, while the elements closest to the inside of the tire focus on wet and winter traction. This changing pattern allows the tire a wider range of performance attributes in various conditions.


Aspect Ratio :-
Aspect Ratio is the ratio of the height of the tyre's cross-section to its width. 65 means that the height is equal to 65% of the tyre's width.

Air Check :-
During an air check, a driver or technician uses a pressure gauge to determine the amount of air currently inflating a tire. You should perform an air check every other time you fill up with gas, each time your tires are rotated, or once a month. Learn more about Air Pressure.

Aqua Planing :-
An extremely dangerous situation where water builds up in front of the tires resulting in the tires losing contact with the road surface. At this point, the vehicle is skimming on the water surface and is completely out of control. Also called hydroplaning.

All-Season Tires :-
Tires that are built to provide good performance all year round. The Rubber Manufacturer's Association defines the specifications for all-season tires. All-season tires have a MS, M/S, or M&S mark on the sidewall, meaning that they are suitable for use in mud and snow.


Alignment :-
Adjusting the vehicle's wheels, steering, and suspension components to manufacturer's specifications. When wheels are in alignment, they are in the optimal position relative to the road and each other. Impacts like driving over a curb or hitting a pothole can cause misalignment.


B

Balancing :-
Tyre balancing is a process to ensure that when the tyre and the wheel spin their weight is equally distributed.

Belt :-
A layer of cords wrapped in rubber, located between the tire tread and the body plies. The cords are usually made of steel, but other materials include fiberglass, nylon, rayon, and polyester.

Bar :-
Metric unit for air pressure. (1 bar = 14.50326 psi).

Backspacing :-
Also known as rearspacing, this is the distance from the mounting pad to the back edge of the rim. Not to be confused with wheel offset. Wheel Backspace Calculator can help you to calculate the wheel backspace.


Bead :-
A ring of steel wire within a rubber wrapper that helps to hold the tyre to the rim.

Bead Chafer :-
A key tire component that acts as the contact point between the tire and wheel. The bead chafer is designed to withstand the force the wheel exerts on the tire during mounting, as well as the dynamic forces of driving and braking.


Bead Filler :-
Component that transfers propulsion and braking torque from the wheel rim to the road surface contact area.

Bead Tension Structure :-
Two sidewall plies wrapped around each bead wire in opposite directions, providing lateral stability and flex to absorb road irregularities.

Bolt Circle :-
The diameter of an imaginary circle drawn through the center of each lug nut hole and then measured from two holes that are directly across from each other. The measurement is used in selecting the proper wheel for replacement.

Bolt Pattern :-
The arrangement of bolt holes on a wheel. Some wheels have more than one bolt pattern on the same wheel to accommodate multiple fitments.

Breakaway :-
A term used to describe a loss of traction when negotiating a curve or when accelerating from a standing start. The tires slide against, instead of grip, the road surface.


C

Construction :-
Construction tells you how the Tyre was put together. The "R" stands for radial, which means that the body ply cords, which are layers of fabric that make up the body of the Tyre, run radially across the Tyre from bead to bead. "B" indicates the Tyre is of bias construction, meaning that the body ply cords run diagonally across the Tyre from bead to bead, with the ply layers alternating in direction to reinforce one another.


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Contact Patch :-
The part of the tire that comes into contact with the road. Also known as the footprint.

Camber :-
Measurement, in degrees, of the wheel’s inward tilt when viewed from the front. Camber is one of the settings adjusted during alignment.


Camber Thrust :-
The centrifugal force generated when a tire rolls with camber, which can add to or subtract from the side force generated by a tire.

Carcass :-
The supporting structure of the tire consisting of plies anchored to the bead on one side and running in a radius to the other side and anchoring to the bead. Also called casing.

Carrying Capacity :-
At a given air pressure, how much weight each tire is designed to carry. For each tire size, there is a load inflation table to ensure the inflation pressure used is sufficient for the vehicle axle load.

Center line :-
An imaginary line down the center of the vehicle. This line aids in measuring a vehicle’s alignment.


Centrifugal Force :-
Physicists call centrifugal force a pseudo or fictitious force because it doesn’t really exist. You experience centrifugal force when sitting in a turning car. The turn produces the sensation of movement, even though there’s no force being applied to your body.
Cold Inflation Pressure :-
Refers to the amount of air pressure in a tire, measured in pounds per square inch (PSI), before a tire experiences heat buildup from driving.


Compliance Cushion :- 
An added rubber component between the tire tread and belt. It absorbs road irregularities for a smoother ride.

D

DOT :-
"DOT" means the tyre is compliant with all applicable safety standards established by the U.S. Department of Transportation (DOT). Adjacent to this is a tyre identification or serial number; a combination of numbers and letters with up to 12 digits.

Directional Tread :-
Tires with directional tread are made to roll in one direction only. As a result, directional tires are used on one side of the vehicle; when they're rotated they move from front to back.

Deflection :-
The area where the tread and sidewall flex when the tread makes contact with the road.

Dry Traction :- 
Describes the tire’s ability to grip the road under braking and acceleration. 

Dry Zone :-
Large tread blocks placed along the outer edges. They help provide confident handling on dry roads.

Dynamics Imbalance :-
When the weight of a tire and wheel assembly is equally distributed around its circumference and on either side of its centerline. If a tire and wheel assembly goes out of dynamic balance, it will produce a wobbling effect or side-to-side shake.

E
Eccentric Mounting :-
Occurs when a tire and wheel assembly is mounted so that the assembly’s center of rotation isn’t aligned with hub’s center of rotation.

ECE Symbol :-
ECE stands for “Economic Commission of Europe,” a European organization that develops motor vehicle requirements. The ECE symbol means that a tire meets ECE standards for physical dimensions, branding requirements, and high-speed endurance.

Extra Load (XL) :-
A designation indicating that a given tire can carry a higher load. Tires receive this designation if they have a maximum inflation pressure higher than the standard maximum.

F

Flat Spot :-
Irregular wear in an isolated area of a tire's tread.

Foot Print :-
The area of the tyre's tread that is in contact with the ground.


Filament At Zero :-
Refers to individual, spiral-wrapped nylon or aramid/nylon reinforcing filaments that may be precisely placed in specific portions or across the entire tread area atop the steel belts banded at zero degrees. This helps retain tire shape, while enhancing steering precision and ride quality.

Free Radius :-
The radius of a tire and wheel assembly when not deflected under load.

Friction :-
Refers to the resistance of one material (the tire tread) as it moves against another (the road). Every tire uses friction to grip the road.


G

Grooves :-
Circumferential channels between the tread ribs of a tire.

Gross Axle Weight Rating :-
Refers to the maximum weight that can be distributed among the tires on a given axle. Sometimes abbreviated as GAWR.

Gross Vehicle Weight :-
The actual weight a vehicle when fully loaded with passengers and cargo.

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Gross Vehicle Weight Rating :-
The maximum weight that a vehicle can support, including its own.

H

Hysteresis:-
In reference to Actions and reactions: not all energy applied to a tyre is dispersed. When dealing with an elastic material like rubber energy is always absorbed and this creates heat build-up.

Handling :-
Describes a tire’s responsiveness to handling inputs.

Hydroplaning :-
A condition where water on the road can't be moved out from beneath the tires, causing the vehicle to stop responding to the steering wheel and ride on a layer of water instead of the pavement.


Heat Cycling :-
A method of “breaking in” competition tires prior to initial use. Heat cycling gradually heats the tire in a controlled environment. This heat buildup creates a more consistent traction and longer tread life.






High Flotation Sizes :-
A tire sizing system designed especially for light trucks. These tires have lower sidewalls and wider treads for better traction on sand, soft soil, mud, or other in off-road situations.


High- Performance Tires :-
Tires that can handle, grip, and corner better than standard tires. These tires are rated for operation at higher speeds than their standard counterparts. High-performance tires can also be called maximum performance or ultra-high-performance.


I
Inner Liner:-
 The layer of rubber inside a tubeless tyre which stops air seeping out of the tyre during normal use.

Imbalance :- 
Describes when the tire and wheel assembly’s distribution of mass becomes uneven.

Indentation :-
A normal, safe occurrence where overlapping splices of fabric cords create indentations in the tire sidewall. Indentations don’t occur on treads because of steel cable implementation.

K

Kilo Pascal :-
The metric unit for pressure. One PSI is equal to 6.9 kPa.

L

Load-Carrying Capacity :-
Indicates how much weight a tire is certified to carry at maximum inflation pressure.

Load Index :-
Load Index is a number that corresponds to the maximum load in kilograms that a tyre can support when properly inflated. You will also find the maximum load in pounds and in kilograms moulded elsewhere on the Tyre sidewall.

Load Range :-
Defines a range of maximum loads a tire can carry at a defined pressure.


Loaded Radius :-
The measurement, in inches, from the wheel axle centerline to the ground when the tire is properly inflated for the load.

Loaded Section Height :-
The height of the tire section that makes contact with the road.
Low Profile :-
A term describing a tire with a low relative aspect ratio or series classification (short sidewall, wide tread).


M

Maximum Inflation Pressure :-
The maximum pressure that a tyre can be inflated to.

Metric Tire Size System :-
One system used to describe a tire’s size. It is the standard system of the ETRTO (European Tire and Rim Technical Organization).

Mid Range Tyres:-
Tyres which retail at a lower price than premium brands; the performance of this range shall logically be lower.

“Mini” Spare (also known as A Space Saving tyre):- 
Smaller than the road tyres, this type of Tyre is designed to save space and reduce weight in the vehicle. A temporary measure to get you home these tyres should be changed as soon as possible, these tyres also have a lower maximum speed.

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Mounting :-
The act of putting a tire on a wheel and making sure the assembly is balanced. New tires need to be professionally mounted.

Match Mounting :-
Technique that matches the tire’s harmonic high point with the wheel’s low point, ensuring optimal ride performance.

N

Negative Offset :-
When the wheel mounting face is closer to the brake side of the wheel, moving the tire and wheel assembly out of the fender well.

Negative Camber :-
Alignment style where the tops of the tires are angled in towards the center of the vehicle. Generally used on race cars for improved grip while cornering.

Nominal Section Width:- 
The section width of an inflated tyre mounted on its theoretical rim and indicated in the tyre size designation.


Nominal Rim Diameter:- 
 A size code figure for reference purposes only, as indicated in the tyre and rim size designation.

NHSTA :-
National Highway Traffic Safety Administration.

O
Offset :-
The distance between a wheel’s mounting surface and centerline. This measurement helps technicians understand how the wheel fits in the wheel well.

Original Equipment Manufacturer - OEM :-
Tires selected by a vehicle manufacturer that best match tire performance to vehicle performance characteristics. Also known as the Stock tire size.

Overall Diameter:-
The diameter of the inflated tire, without any load.

Overall Width :-
The distance between the outside of the two sidewalls, including lettering and designs.

Overinflation :-
Too much air in the tire, resulting in premature wear in the center of the tread.


Original Equipment (OE):-
This is the original brand of tyre that was fitted by the car manufacturer. Please note that there may be more than one OE brand fitment.

Oversteer (see also Understeer):-
This is a term used to describe a loss of grip to the rear wheels during cornering causing the car to slide sideways.


P

Pounds Per Suare inch (psi) :-
The imperial unit for air pressure.

Plus-Sizing :-
An option allowing drivers to customize their vehicles by mounting low-profile tires on wider rims (one or two inches greater in diameter), usually enhancing vehicle appearance, handling, and performance. It is recommended that you keep the overall tire diameter within the certain range of the OEM tire size to prevent problems with spedometer, transmission, gas mileage, and braking.

P-Metric :-
Uniform designation of tire sizes, in metric measurements originally introduced by American tire manufacturers in 1977; commonly called P-metric series. A typical P-metric tire is P205/70R14 93S.

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Pneumatic Tire :-
A tire designed to be filled with air.

Positive offset :-
The mounting face of a wheel is toward the wheel’s street side, moving the tire and wheel assembly in toward the vehicle.


Penny Test :-
A simple test to check tire for proper tread depth, using a penny.


R

Radial Ply Tire :-
A type of tire with plies arranged so cords in the body run at 90-degree angles to the center line of the tread.

Revolutions Per Mile (RPM) :-
Measured number of revolutions for a tire traveling one mile. This can vary with speed, load, and inflation pressure.

Ribs :-
A pattern of tread features aligned around the circumference of a tire. There are usually multiple ribs across the tread area of a tire.

Rim :-
That portion of a wheel to which a tire is mounted.

Rim Diameter :-
The diameter of the rim bead seats supporting the tire.

Rim width :-
The measurement between the flanges of a rim.

Rim Drop :-
Also called drop center, a change (drop) in the rim profile between the rim flanges in which the bead area of a tire is placed during the mounting process. This allows the tire to be mounted on the rim.

Rim Flange :-
Surface of the rim of the wheel that contacts the side of the tire bead.


Rolling Circumference :-
The linear distance traveled by a tire in one revolution (its circumference). This can vary with load and inflation. Rolling circumference can be calculated as follows: 63,360 divided by revolutions per mile = rolling circumference in inches.

Rolling Resistance :-

The force required to keep a tire moving at a uniform speed. The lower the rolling resistance, the less energy needed to keep a tire moving.

Rotation :-
The changing of tires from front to rear or from side to side on a vehicle according to a set pattern; provides even tread wear. Rotating your tires on a regular basis (every 6,000-8,000 miles) is a simple way to add miles to their life. See your tire warranty for more information on recommended rotation.





S


Shoulder :-
Where the tire's sidewall meets the tread.

Sidewall :-
The side of the tire, between the tread surface and the bead. The location of information about the tire including size, date of manufacture, construction, and more.

Sipes :-
Small slits within the tire's tread that increase traction in wet and snowy conditions. Sipes work by opening as the tire rolls onto the road, gripping the road surface and keeping more rubber on the road.

Speed Rating :-
Speed Rating is a number that corresponds to the maximum service speed for a tyre. "H" means that the tyre has a maximum service speed of 210 km/h. Please note that this rating relates only to tyre speed capability, and is NOT a recommendation to exceed legally posted speed limits; always drive within the legal speed limits.

Speed Rating Chart :-
Many tyres are available in speed-rated versions to match the speed capabilities of the world’s fastest cars. Generally, it is recommended that a speed-rated tyre be replaced with a tyre having an equivalent or greater speed rating.
In situations where tyres having different top speed ratings are mixed on a vehicle, the maximum speed certification is limited to the top speed certification of the tyre with the lowest speed rating. Speed ratings do not indicate how well a tyre handles or corners. They certify the tyre’s ability to withstand high speed.







Staggering/Staggered Fitment :-
A vehicle that has larger-sized (or wider) wheels on the back axles and smaller wheels on the front. Staggered fitment is most frequently seen on sports cars.


Steel Belted Radial :-
A radial tire made with steel belts (rather than fabric belts).

Studs :-
Metal or plastic pins that can be inserted into the tread of a studdable tire to increase traction in severe ice and snow.

Section Height :-
The height of a tire, measured from its rim to its outer tread. 

Service Description :-
Numbers and letters molded into the sidewall indicating the load-carrying capacity, load index, and the speed rating.

Shimmy :-
Describes the wobbling, side-to-side motion that may occur at the front of the vehicle, felt through the steering wheel. Misalignment, worn steering components, or dynamic imbalance can cause shimmy.

Section width :-
The distance between the outside of a tire’s sidewalls, not including any lettering or designs.

Slip :-
The difference between a vehicle’s linear speed and the rotational speed of a tire. For example, a tire that is locked and sliding while a vehicle isn’t moving is operating at -100% slip.

Slip Angle :-
The difference between the direction the wheel is traveling and the direction a vehicle is traveling.


Stability :-
A tire’s ability to respond to steering inputs and external forces.

T


Tyre :- 
Made of a mixture of rubber, chemicals, fabric and metal, their job is to give the car traction on the road in a variety of conditions, and to cushion the car from shock.

Tyre Type :-
Tyre type defines the proper use of the Tyre. “P” means this is a Passenger car Tyre. If the Tyre had an “LT” then the Tyre would be for a Light Truck.

Tyre Width :-
Tyre Width is the width of the tyre measured in millimetres from sidewall to sidewall. This tyre is 215 millimeters.

Tire Size :-
A collection of numbers and letters that tells you the tire width, sidewall height (aspect ratio) and wheel diameter, among other information. For example, the tire size 225/45R17 tells you that the tire has a width of 225 millimeters, an aspect ratio of 45%, and a wheel diameter of 17 inches. Tire size can be found on the sidewall of a tire.

Tyre Grades :-
Tyre Grades: Uniform Tyre Quality Grading System or UTQG
Except for snow tyres, the DOT requires the manufacturers to grade passenger car tyres based on three performance factors: tread wear, traction, and temperature resistance. The UTQG rating of each passenger car and light truck tyre is listed in the Car/Light Truck Tyre Catalogue.

TPMS :-
TPMS stands for Tire Pressure Monitoring System. It’s a safety system built into your vehicle (or retrofitted) that monitors your tire pressure, and alerts you when the pressure in one or more tires falls to an unacceptable level.

Tread :-
The outer layer of a tire; the part that comes into contact with the road.

Tread Depth :-
Measurement from the bottom of a tire's tread grooves to the tread surface, measured in 32nds of an inch. New car tires generally have a depth of 10/32" or 11/32" (truck tires and winter tires are usually deeper); tires are considered worn out at 2/32" (or in some cases, earlier).

Tread Life :-
The expected service length of a tire before it wears out, measured in miles.

Tread Wear :-
  • More Than 100 - Better
  • 100 - Baseline
  • Less Than 100 - Poorer

The tread wear grade is a comparative rating based on the wear rate of the tyre when tested under controlled conditions on a specified government test track. A tyre graded 200 would wear twice as long on the government test track as one graded 100. Your actual tyre mileage depends upon the conditions of their use and may vary due to driving habits, service practices, differences in road characteristics and climate. Note: Tread wear grades are valid only for comparisons within a manufacturer's product line. They are not valid for comparisons between manufacturers.


Traction :-
  • A - Best
  • B - Intermediate
  • C - Acceptable
Traction grades represent the tyre's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The Traction grade is based upon "straight ahead" braking tests; it does not indicate cornering ability.

Temperature :-
  • A - Best
  • B - Intermediate
  • C - Acceptable
The temperature grades represent the tyre's resistance to the generation of heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperatures can cause the materials of the tyre to degenerate and thus reduce tyre life. Excessive temperatures can lead to tyre failure.

Tire Placard :-
A metal or paper tag permanently affixed to a vehicle, which indicates the appropriate tire size and inflation pressures for the vehicle. The placard can ordinarily be found on either the driver’s doorpost, the glove box lid, or the fuel-filler door.

Tire Pressure Gauge :-
Tool used to properly measure the air pressure in a tire.




TOE :-
Describes the symmetry between two horizontally situated tires, when viewed from above. Toe-in means that the tire front ends veer inward toward the engine. Toe-out refers to tire front ends that veer outward toward the road. Toe is adjusted during alignment.

TOE-Out Turns :-
Describes how a vehicle’s wheels on the inside of a turn follow a smaller radius than those on the outside. This occurs because the two front wheels steer at different angles when turning.

Torque :-
Turning or twisting effort. Usually measured in lb-ft or Newton meters.

Torque Locking Sipes:-
Sipes with vertical undulation for added rigidity during cornering.


Torsion Bar :-
A long, straight bar fastened to the vehicle frame at one end and a suspension part at the other. This component acts like a coiled spring that absorbs energy by twisting.




Touring Tires :-
Tire type offering a balance of ride quality and performance attributes. Touring tires occupy the middle ground between passenger and performance tires.
U

UTOG :-
"UTQG" stands for Uniform Tyre Quality Grading, a quality rating system developed by the Department of Transportation (DOT).

Ultra-Low Profile Technology :-
Specialized sidewall shape, bead area, and bead compound that enhance the durability and mountability of tires with very short sidewalls.

Ultra-High Performance Tires:-
Tire type engineered for the most sophisticated and capable sports cars. UHP tires provide the maximum level of performance attributes, including optimal cornering response and high speed stability.




Underinflation :-
Underinflation occurs when tires aren’t filled with enough air, and can happen naturally over time. Underinflation can cause premature tire wear and reduce fuel economy. Find more detail about tire inflation on our Determining Correct Air Pressure page.




Understeer :-
Handling characteristic in which the front tires break loose because they are running a larger slip angle than the rear tires.




Undertread :-
Material between the bottom of the tread rubber and the top layer of steel belts. It acts as a cushion that enhances comfort



.

Uni-Directional Tread :-
A tire designed to only rotate in one direction. Also called directional tread.




Unsprung Weight :-
The weight of the vehicle’s components not supported by its springs, including wheels and tires, outboard brake assemblies, the rear axle assembly, suspension members, springs, shock absorbers, and anti-roll bars.

V

Valve :-
A device that lets air in or out of a tire. It is fitted with a valve cap to keep out dirt and moisture, plus a valve core to prevent air from escaping.


Valve Assembly :-
Device that lets air in or out of the tire. Includes the valve core which keeps air from escaping, the valve stem (tube), and the valve cap/cover to keep out dirt and moisture.

Vehicle Placard :-

A sticker that contains a variety of important information about your vehicle's tires, including the vehicle manufacturer's recommendations for tire size, tire pressure, load carrying capacity, and speed rating. Usually located on the driver's side door jamb.

Variable Angles Sipes :-
Tread blocks with siping set at three different angles to enhance lateral grip.

Variable Contact Patch :-
A system that maximizes the contact patch area during cornering through a combination of asymmetrical tread patterns and underlying belts.

Variable Integrated Pitch :-
Process where different-sized tread blocks are placed around a tire’s circumference to minimize noise.


Vertical Bouncing :-
Occurs when a vehicle’s weight isn’t evenly distributed around the wheel’s axis of rotation. You can feel this through the floor, seat, and steering column.

Viscous Planing :-
Road condition that can occur when rain wets a formerly dry surface, causing oil on the road surface to rise up and sit on the fresh moisture. Can be very slippery, even when the moisture is very thin. Continuing rain lessens this condition by washing the oil away.

Vulcanization :-
The irreversible process of heating rubber under pressure to improve its strength and resilience.

W

Wheel Weights :-
Small weights attached or secured to the wheel to balance the tire and wheel assembly.

Wheel Diameter :-
Wheel Diameter is the width of the wheel from one end to the other. The diameter of this wheel is 15 inches.

Winter Tires/Snow Tires :-
Tires built with a special tread compound and tread pattern to optimize traction in winter weather conditions. Winter tires are branded with the "mountain/snowflake" symbol on the sidewall.


Wander :-
A vehicle’s tendency to stray or wander from its intended direction of travel as a result of steering abnormalities, worn tires, suspension misalignment, crosswinds, or pavement irregularities.

Wet Traction :-
Describes a tire’s ability to provide grip and vehicle control on wet roads, as well as resistance to hydroplaning.

Wheel Base :-
The longitudinal distance from the front wheel center to the rear wheel center on the same side of the vehicle.

Z

Zero Offset :-
When the mounting face of the wheel directly aligns with the wheel’s center line.

Zero Toe :-
When tires on the same axle are parallel. The fronts and rears of the tires are equidistant.

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