Tire Terms
Air Pressure
Check the pressure in your tires at least monthly and before long trips when your tires are cool (after the vehicle has been stopped 3 hours and then driven less than one mile). Adjust to the vehicle manufacturer’s specified pressure while tires are cold. Never bleed or reduce the air pressure when tires are hot. It is normal for pressure to build up as a result of driving. Use an accurate tire gauge to check pressure and maintain it at the level recommended by the vehicle manufacturer. Don’t forget your standard size or temporary spare tire. Your temporary spare – it requires a higher inflation pressure. Remember: Under inflation is the most common cause of sudden air loss or sudden failures in any kind of tire and may result in unexpected loss of vehicle control or accidents.
Alignment of Vehicle
A wheel alignment adjustment may be necessary if the vehicle pulls to the right or the left with the steering wheel is in straight ahead position. Another indicator of the need for an alignment check is if tires are wearing unevenly.
All Season Tires
All season tires can be used throughout the year. The following markings appear on the sidewall of the tire: M+S, M/S or M&S. This meets the RMA definition of a mud and winter tire. However, there are also tires designed for severe snow conditions. These tires will show a symbol of a mountain with a snowflake next to the MS letters & are designed as winter tires. Tires designed for use in severe snow conditions generally have tread patterns, structure and materials to give superior performance. These tires are marked with the “M+S” designation plus a mountain/snowflake symbol.
ABS / Anti-Lock Brake System
Under emergency braking using conventional braking systems the wheels can lock up, making the car un-steerable. ABS systems provide continuous monitoring and control of the braking force and in some circumstances can reduce the braking distance while maintaining full car steer ability. Modern high-quality tires are optimized and matched to the ABS functions. And “braking on wet roads with ABS and ABS-brakes” are already often a standard test required by auto manufactures for many tire test specifications.
ASR / Anti-slip-control
ASR is fitted to vehicles to prevent wheels slipping, spinning on slippery or uneven surfaces. Electronic sensors are used to control and dose the power transmitted to the drive axle, in order to ensure that tires can properly and reliably grip the road during acceleration.
Aquaplaning
The contact area of the tire to the road is reduced when by water is on the road. In extreme cases, the vehicle “hydroplanes (glides) on the water”. This will drastically reduce the control of the vehicle. Tires have special tread patterns that ensure optimum drainage of the water away from the tread surface. This effect does however reduce proportionally as speed increases. The most effective protection is to adjust driving speeds to the weather conditions.
Balancing
At high speeds, tires generate enormous centrifugal forces. Even tiny irregularities in the tire of only a few grams are multiplied by many orders of size. Such imbalance stresses tires and suspension. This weight irregularity can be tested and identified at in tire dealerships and is balanced by adding small counter-weights. Every time a tire is fitted to a wheel, it should be balanced.
Bead
The bead of the tire is that part which sits on the rim. At the center of the bead is the core, which comprises a bundle of steel wires embedded in rubber. This provides a safe and solid seating of the tire on the rim.
Braking distance
The distance required for braking depends on the speed of the vehicle, the condition of the road surface and the condition of the tires, in particular the tread. Check the tires tread depth regularly and change your tires when worn down to the “tread wear indicators” located at the bottom of the tread grooves.
Camber
The purpose of wheel camber is to reduce friction during cornering. The camber is measured when the wheels are standing on a flat surface. The difference from the vertical (inward or outward tilt of the tire) is then referred to as either positive or negative camber.
Casing
Modern tires are made of many different materials and components. Looked at schematically, there is the outer cover – the tread and sidewall, and the substructure, the casing. Casing components may include steel and/or textile cord plies, the inner liner (to make tube-less tires airtight), sidewalls, the apexes, the bead core (keeps the tire on the rim) and the bead reinforcement.
Chains
Even modern winter tires can sometimes not help when there are huge amounts of snow and steep gradients. In these situations traction, lateral control and reliable braking require tire chains. In order to be prepared it is recommended to try and fit chains in a “dry run”. Snow chains have to be draped over the drive wheels. Please also note that a maximum speed is given. With some low profile tires a problem can result: the reduced space between the tires and the wheel arch leaves no room to fit snow chains.
Date of Manufacture
The date of manufacture of a tire is indicated on the tire’s sidewall at the end of the DOT serial number. Tire manufacturers have adopted a standard identification system: four numbers, which indicate the week and the year of manufacture. For example, the figures 0201 indicate that the tire was made in the second week of the year 2001.
Direction of Rotation
On standard tires with symmetrical tread patterns, it does not matter which way the tire is fitted on the rim and in which position it is fitted on the car. Some tire manufacturers have, however, started producing tires with specific directions of rotation in order to improve wet grip and optimize noise generation. The direction of rotation is marked on the side of the tire with an arrow. This side of the tire must be on the outside, and the tire must roll forwards in the direction of the arrow for optimum tire performance. A number of tires with asymmetric tread patterns are also now available which do not have a specific direction of rotation.
DOT Serial Number
The “DOT” symbol certifies the tire manufacture’s compliance with the U.S. Department of Transportation tire safety standards. The DOT serial number is located on the lower sidewall of the tire, on one side only. Below is a description of the serial number. Starting in the year 2000, four numbers are used for the Date of Manufacture, first two numbers identify the week and the last two numbers identify the year of manufacture. Prior to year 2000 three numbers are used for the Date of Manufacture, first two numbers identify the week and the last number identifies the year of manufacture. To identify tires manufactured in the 90’s a decade symbol (a triangle on its side) is located at the end of the DOT serial number.
For Example: DOT NJ HR 2AE2 529 529
– DOT: Reference Symbol (certifies the tire manufactures compliance with U.S. Department of Transportation tire safety standards).
– NJ: Manufactures Plant Identification Code
– HR: Tire Size Code Number.
– 2AE2: Tire Type Code (coding for type of tire optional by manufacture).
– Date of Manufacturer: 529 (52nd week of 1999) or 5200 (52nd week of 2000).
ESP / Electronic Stability Program
An Electronic Stability Program, ESP, helps master critical driving situations, for example when the vehicle suddenly over steers during cornering or when sudden evasive action is required. The systems detects skidding movements within fractions of a second and can take corrective action. ESP systems not only function when road conditions are good, but also on wet, on icy and on unpaved roads. Technically speaking, The ESP system combines the ABS / Anti-Lock Brake Block System, electronic braking pressure distribution, ASR / Anti-slip-control and yaw control.
Emergency Mobility Systems
If a tire punctures and looses air, a standard size or a temporary special spare tire must be put on in order to continue the journey. In order to avoid the troublesome, sometimes dangerous procedure of changing a tire on an open road, various manufacturers now offer so-called emergency mobility systems. What these tires have in common is that when all air pressure is lost the rim does not destroy the tire. The journey can be continued without changing the tire – over a limited distance at a restricted speed.
Load Index, Ply Rating or Load Range
These symbols are found on the sidewall of the tire indicating the load – carrying capacity of the tire.
Mixing Tires
It is recommended that all four tires be of the same size, construction and speed rating. If tires of different speed rating are mounted on a vehicle, the vehicle speed capability will be limited to the lowest speed-rated tire on the vehicle. It is recommended that the lower speed-rated tires be placed on the front axle regardless which axle is driven. This should be done to prevent a potential oversteer condition. Vehicle handling may also be affected. Consult the tire manufacture.
Radial Tires
Radial tires have body cords that run across the tire nearly perpendicular to the beads. Radial tires have belt plies, which are laid diagonally under the tread to stabilize and strengthen the tread area and add flexibility to the sidewall. By restricting tread movement during contact with the road, the belt plies increase improve tread life, traction and improve handling.
Reinforced or XL (extra load) Tires
Reinforced or XL (extra load) tires are specially reinforced tires. They can carry higher loads than a tire of the same size. Reinforced tires are designated on the Sidewall by the letters “RF”, extra load tires with the letters “XL”. Reinforced and XL tires require need higher inflation pressures compared to standard tires.
Revolutions Per Mile (RPM)
The number of revolutions a tire makes in one mile, at a given load, speed and inflation. Sometimes called RPK or revolutions per kilometer.
Rolling Resistance
The drag force required to put a free rolling tire into motion. Tires are not rigid, but flexible. During driving the tires compress, and flex. This flexing absorbs energy, converting it into heat. In order to reduce rolling resistance, manufacturers use special rubber compounds. Any reduction in the rolling resistance of the tire helps reduce fuel consumption. Since rolling resistance also increases with low inflation pressure, it is beneficial to check the pressure of tires regularly.
Rotation
Refer to your Vehicle Owners Manual for recommended rotation pattern and interval for your vehicle. If not available, follow one of the patterns shown below. It is recommended to rotate your tires every 6,000 to 8,000 miles, or sooner if uneven treadwear begins to appear. The purpose for regular rotation is to achieve more uniform treadwear on all tires on your vehicle. If tires show uneven treadwear, ask the serviceperson to check and/or correct any alignment or other mechanical problem before rotation. This is true for both front wheel and rear wheel drive vehicles. Full size spare spare tires should be included in the rotation pattern for your vehicle. Compact spares (temporary use spares) should not be included in the rotation pattern.
Speed Symbol
Speed ratings for tires are identified by means of a speed symbol shown on the sidewall of a tire. The maximum speed for these symbols in shown in the table. Although a tire may be speed rated, tire manufactures do not endorse the operation of any vehicle in an unsafe or unlawful manner. Furthermore, tire speed ratings do not imply that a vehicle can be safely driven at the maximum speed for which the tire is rated, particularly under adverse road and weather conditions or if the vehicle has unusual characteristics. Speed ratings are based on laboratory tests which relate to performance in the road, but are not applicable if tires are under-inflated, overloaded, worn out, damaged or altered. Example: Tire size P215/60R15 H 185/65 R 15 H: the H indicates a maximum permitted speed of 130 MPH.
Temporary Spare Tires
Temporary spares are designed to carry the same load as the standard size tire on your vehicle and can be applied to any position. Maintain the proper inflation pressure as shown on the sidewall of the tire, it requires a higher inflation pressure than a standard size tire. Refer to the information on the sidewall of the tire for proper usage & speed restrictions. With such a tire, a vehicle may be operated until it is convenient to repair or replace the disabled tire. Have your standard tire repaired or replaced as soon as possible, then return the temporary spare to the trunk to conserve its use-able tread life. The temporary tire can be worn down to the tread wear indicators, same as your standard tire. At such time the tire must be replaced.
Toe
The toe describes the distance between the centerlines of the tires on an axle. The toe setting can be adjusted on all cars. Since most wheels tend to run towards the outside because of the camber, most cars are set with a slight positive toe-in. This means that the wheels are slightly closer together at the front than at the back. Incorrect settings for your vehicle result in uneven tire wear. If you notice uneven tire wear, then have your vehicle alignment settings checked.
Tread
The tread is that part of the tire with the groove pattern which is in contact with the road. The tread is specifically design to provide traction for stopping, starting, cornering and provide long lasting wear.
Tread Depth
The measured distance from the tread surface to the bottom of the main grooves away from the Tread Wear Indicators. Usually specified in 1/32 of an inch.
TWI (tread wear indicator)
Tread wear indicators (“wear bars”) are located at the base of the main grooves and are equally spaced around the tire. Always remove tires from service when they reach a remaining tread depth of two thirty-seconds of an inch (2/32″). If not corrected, wet weather accidents are more likely to happen due to skidding on bald or nearly bald tires. Also, excessively worn tires are more susceptible to damage from road hazards. Built-in treadwear indicators, or “wear bars,” which look like narrow strips of smooth rubber across the tread, will appear on the tire when that point of wear is reached. When you see these wear bars, the tire is worn out and it’s time to replace the tire.
Tire Size Designation
The dimensions of a tire are detailed on the sidewall. In the case of a P185/65R 14 tire, the figures mean the following: 185 = width of tire in mm; 65 = the ratio of the height to the width as a percentage; R = radial construction; 14 = diameter of the rim in inches.
Tire Storage
Tires should be stored in a dry, cool place, away from sunlight and sources of ozone, such as electric motors. If you must store tires flat, (one on top of the other), make sure you don’t stack too many on top of each other. Too much weight can damage the bottom tire. Also be sure to allow air to circulate around all sides of the tires, including underneath, to prevent moisture damage. If storing tires outdoors, protect them with an opaque waterproof covering and elevate them from the ground. Do not store tires on or over black asphalt or other heat-absorbent or reflective surfaces, such as snow-covered ground or sand. Solvents, fuels, lubricants and chemicals should be kept out of contact with tires. Spare tire carriers on your vehicle are not intended to be used for long term tire storage. If your vehicle has a full size tire (same size and type tire recommended for use by the vehicle manufacture not temporary use spares) as a spare, it should be included in the tire rotation pattern.
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 wrong to link treadwear grades with your projected 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.
Temperature
The temperature grades, from highest to lowest, are A, B and C. These represent the tire’s resistance to the generation of heat when tested under controlled conditions on a specified indoor laboratory test wheel.
Valve
The valve, fitted in the wheel, ensures that the tire can be filled with air. The correct valve is required for the correct wheel/tire assembly, this is the job of the tire dealer. The cause of a slow loss of air pressure can be a defective valve. The valve cap should always be fitted to the valve in order to protect the valve core from dirt and moisture.
Valve Cap
The valve cap, although small, has a very important job: it protects the sensitive valve internals from dust, dirt and humidity. If valve caps are lost they should be replaced immediately in order to avoid expensive damage later.
Winter Tires
In snowy areas, many cities and counties have “snow emergency” regulations which are invoked during heavy snowfalls. Check with authorities for the rules in your area. Under some rules, motorists are subject to fines if they block traffic and do not have winter tires on their vehicles. You can avoid this by equipping your vehicle with winter tires marked with “MS,” “M&S,” or “M + S” on the sidewall and severe snow marking. If you change to winter tires, be sure they are the same size and construction type as the other tires on the vehicle. It is recommended that winter tires be applied on all four positions. It is acceptable to install winter tires only on the rear position of a rear wheel drive vehicle. If winter tires are installed on the front position of any vehicle, the MUST also be installed on the rear position. Without winter tires on the rear, vehicle handling can be adversely affected. This may result in loss of vehicle control which could cause serious injury or death. If winter tires with a lower speed rating than listed on the vehicle placard are installed for use in winter conditions, the speed capability of the vehicle is reduced to the speed rating of the winter tires. In areas where heavy snowfalls are frequent, many drivers carry chains for use in emergencies, or have their tire dealer apply studded winter tires or install tires for use in severe snow conditions. Most states have time limits on the use of studs. Before installing studded tires, check the regulations in your area. If studded tires are applied to the front axle, they also must be applied to the rear axle. If you use chains, make sure they are the proper size and type for your tires, otherwise they may damage the tire sidewall and cause tire failure. Tires designed for use in severe snow conditions generally have tread patterns, structure and materials to give superior performance. These tires are marked with the “M+S” designation plus a mountain/snowflake symbol.
