tyres sidewall

8/13/2019 Tyres Sidewall

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Shoreline Motoring: Wheel Results

TIRE TECH

Reading Sidewall Info

Plus Sizes

BRAKE TECH

What Stops Your Vehicle

Brake Performance

SUSPENSION TECH

Suspension Safety

WHEEL TECH

Wheel Finishes

Sidewall 101

In recent years, the trend of performance and sty ling enthusiasts has been toward making sidewalls smaller,which just makes them more important than ever. The sidewall of a tire is an owner's manual. It containsinformation needed to ensure your safety and optimum performance of your vehicle. The designations andclassifications that appear on it identify everything from common dimensions to standard test identificationnumbers. Being able to read and understand sidewall moldings will help you better understand theperformance of each tire and make the right choice for your vehicle and needs.

This page could have been made shorter, but we at Shoreline wanted to provide the information for ourcustomers. Its all important, but some of it may not be important to you, so feel free to scan this pagequickly for the answer to a specific question, or skip over sections t hat dont apply.

Aspect RatioA tire's aspect ratio is the relationship of the tire's section height to section width expressed as a percentage.The lower the aspect ratio, the shorter the sidewall, and in most cases, the quicker the steering response.When the aspect ratio appears in the sizing of a tire, it precedes the tire construction designation, except inthe Alpha-Numeric system.

Passenger Tire SizingThree sizing systems exist for passenger tires today: P-Metric, European Metric and Millimetric. Each of thesesystems evolved from the numeric system, which was first tire sizing system and is now obsolete. It wasdeveloped when all tires had the same aspect ratio, and provided only the nominal cross section width of thetire and the rim diameter in inches. The following examples show three sizing systems that are commonly

seen today.Today, most tire manufacturers build tires that conform to the P-Metric system. Based on the metric system,it evolved in the late 1970s in an attempt to standardize tire sizing worldwide. Several variations of eachsystem may be used.P215/65SR15 P215/65R15 P215/65R15 95SP = Passenger car tire215 = section width in millimeters65 = aspect ratioR = radial construction15 = wheel diameter in inches95S = service description (load index and speed rating)

European Metric is a conversion of the numeric system from inches to millimeters. Aspect ratio appears inthe size designation in most cases where it is other than 82.

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155SR13 155R13 155R13 78S155 = section width in millimetersS = speed ratingR = radial construction13 = wheel diameter in inches78S = service description (load index and speed rating)185/70SR14 185/70R14 185/70R14 88S185 = section width in millimeters70 = aspect ratio

S = speed ratingR = radial construction14 = wheel diameter in inches88S = service description (load index and speed rating)

The Millimetric system is best remembered for its use with Michelin TRX tires, which were fitted to certainEuropean performance sedans in the 1980s. In its time, the tire offered excellent performance, but it hasbeen obsolete for more t han a decade. Replacement tires are available from vintage-tire replica sources, butit is generally more satisfactory to convert to standard wheels and modern P-Metric or European Metric tires.240/55R390240 = section width in millimeters55 = aspect ratioR = radial construction390 = wheel diameter in millimeters

Light Truck Tire SizingSizing for light truck tires accounts for the performance requirements of the vehicle and its tires, which haveevolved with the expanded uses of trucks and vans for work, recreation and passenger transport. There arethree light truck tire sizing systems: Light Truck Metric, Light Truck High Flotation and Light Truck Numeric.The Light Truck Metric system mirrors the P-Metric system, and P-Metric tires are in fact sometimes used inlight truck applications when load capacity and other safety considerations are satisfied.LT235/75R15/CLT = light truck designation

235 = section width in millimeters75 = aspect ratioR = radial construction15 = wheel diameter in inchesC = load range

Light truck high flotation tires evolved in the mid-1970s as lower aspect ratio tires became more popular onlight trucks and vans. The combination of lower aspect ratios and high flotation yielded bett er traction onsand and soft soil found in off-road situations.31X10.5R15LT/C31 = overall diameter in inches

10.50 = section width in inchesR = radial construction15 = wheel diameter in inchesLT = light truck designation



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C = load range

The Light Truck Numeric system is still widely used on commercial vehicles.9.50R16.5LT/D9.50 = section width in inchesR = radial construction16.5 = wheel diameter in inchesLT = light truck designationD = load range

Speed Rating

A tires speed rating indicates the range of speeds at which the tire can carry a load under specified serviceconditions. The speed rating system used today was developed in Europe to ensure the safe performance oftires at standard speeds. A letter indicates a tire's certified speed rating, ranging from 5 km/h (3 mph) toabove 300 km/h (186 mph). The speed rating system describes the top speed for which a tire is certified. Itdoes not indicate the total performance capability of a tire.

When the speed rating system was originally developed, the Unlimited V category of over 210 km/h (130mph) was the top speed rating a tire could achieve. As manufacturers made more tires that fit into thiscategory, it was necessary to better regulate performance at high speeds to ensure safety in unlimited speedzones. The Limited V category of 240 km/h (149 mph) was then created, and the Z speed rating was added

as the top speed rating t hat a tire could achieve. Wand Y limited speed symbols have been added as higherspeed categories.Always consult the manufacturer for the maximum speed of Unlimited Z tires. Speed rating is identified as apart of the tire's sizing or service description. In the latest attempt to standardize tire designations, allratings except unlimited ZR incorporate the speed symbol and load index as the t ire's service description.

For example:205/60R15 91V205 = section width in millimeters60 = aspect ratioR = radial construction15 = wheel diameter in inches

91 = load index serviceV = speed symbol description" ZR" Rated Tires

When "ZR" appears in the size designation with the service description, the maximum speed is as indicatedby the service description.P275/40ZR17 93W 270 km/h (168 mph)P275/40ZR17 93Y 300 km/h (186 mph)

For tires having a maximum speed capability above 240 km/h (149 mph), a "ZR" may appear in the sizedesignation. For tires having a maximum speed capability above 300 km/h (186 mph), a "ZR" must appearin the size designation. Consult the tire manufacturer for maximum speed when there is no servicedescription.



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Load Index

The load index ranges from 0 to 279 and indicates the load capacity of a tire. Most passenger car tire loadindices range from 75 to 105. Using a previous example of tire size 205/60R15 91V, the load index of 91corresponds to a load carrying capacity of 615kg (1356 lb) at maximum inflation pressure. The speed symbolof the tire is the second part of the service description.The service description system is used with all tires except Unlimited Z. For Unlimited Z rated tires, consultthe vehicle manufacturer for maximum speed. For proper load carrying capacity, consult the "High-SpeedDriving for Passenger Tires" section of this guide.Please note the load values in the table are derived from European Tyre and Rim Technical Organization(ETRTO, European) standards and correspond to European metric tires. For P-metric tires, the maximumload is derived from Tire and Rim Association (T&RA, American) load formulas and can be found in t he datapages or on the tire. Some T&RA load values are rounded to the nearest load index value. This should clarify

why sometimes the same load index for European and P-metric sizes show different maximum load values.



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One pound is equal to .4536 kg.One kg is equal to 2.2 lb.

Uniform Tire Quality Grading

The Uniform Tire Quality Grading System (UTQGS) provides information in three categories: treadwear,traction and temperature. Each tire manufacturer performs its own tests in each area, following government-prescribed test procedures. Each manufacturer then assigns grades that are branded on the tire. This isknown as Uniform Tire Quality Grade Labeling (UTQGL).

Example: 300 AA A300 =treadwearAA =tractionA =temperature

Treadwear

Treadwear grades typically range from 60 to more than 600, in twenty-point increments. The actual life ofany tire is determined by the road surface quality, driving habits, inflation, wheel alignment and rotationpractices.



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Treadwear ratings are determined on a 400-mile government test course covering specified sections ofpublic roads near San Angelo, Texas. A group of not more than four test vehicles travels the course in aconvoy so that all tires experience the same conditions. Tread groove depths of the tires being tested aremeasured after each 800 miles. The same procedure is followed for a set of control, or "course monitoringtires."

Upon completion of the 7,200-mile test the rating results of both tests are compared, and the tires beingtested are assigned a treadwear rating by the manufacturer. This test does not necessarily simulate theactual conditions under which a given tire is designed to perform, so there is no reliable way to equate miles

of wear to treadwear grade points.The best way to use treadwear ratings when choosing tires is to compare one rating to another for a tire ofsimilar design. For instance, a tire with a treadwear grade of 400 might be expected to last twice as long asa tire that has a grade of 200. However, a tire with a higher treadwear rating may be quickly destroyed ifused outside its intended performance envelope, whereas a tire intended for such use may have a muchlower treadwear rating but last much longer under the conditions.

TractionTraction grades indicate a tire's ability to stop a car in straight-ahead motion on wet test surface pavementwith the wheels locked. UTQG traction tests are performed in straight-ahead sliding on government-maintained concrete and asphalt skid surfaces that have a specified degree of wetting to simulate most road

surfaces in a rainstorm.

Twenty measurements are taken with an industry standard control tire on an asphalt surface and averaged.The same number of measurements is made on a concrete surface. Corresponding measurements are thenmade on the tires being tested. Once the results of the tests are compared, traction ratings based ongovernment prescribed coefficient levels are assigned to the tires. Traction grades include AA, A, B, C, withAA being the highest attainable grade.UTQG traction ratings may not apply to straight-line acceleration, cornering traction or peak values ofstraight-ahead braking force like those experienced in non-skid braking tests.

TemperatureTemperature grades also range from A to C, with A being the highest. Temperature grades represent aproperly maintained tire's ability to dissipate heat under controlled indoor test conditions. Temperatureratings are determined by running tires on an indoor road wheel t est under specified conditions. Successive30-minute runs are made in 5-mph increments starting at 75 mph and continuing until the tire fails. A tire isgraded "C" if it meets the minimum performance required by the U.S. Department of Transportation. Gradesof "B" and "A" represent higher levels of performance than the minimum required by DOT.

Maximum Load and Maximum InflationMaximum load and inflation indicate the maximum load that can be carried at the tires maximum allowableinflation pressure.

Example:

MAX.LOAD 990 kg (2183 LBS.) AT 280 kPa (41 psi) MAX. PRESS.Light truck tire sizes show specific load range symbols on the sidewall that indicate how much load the tire isdesigned to carry at a specified pressure. Many light truck size tires are Load Range C, meaning that they



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carrying capacity, load range D or E tires can be used, provided the wheels can carry the increased load andpressure. Otherwise, new wheels are required.

Note: For most load range C, D, and E tires and/or light truck applications, the load-carrying capacitydesignation appears directly after the tire size as below:LT235/75R15/C

The load capacity of P-Metric tires is rated Light Load, Standard Load or Extra Load. Light and Standard Loadtires are limited to the load that can be carried with a maximum inflation pressure of 35 psi. L ight Load tiresoffer a slight load reduction from Standard Load tires for certain applications. Light load applies only to tireswith aspect ratio of 45 or less. Extra Load tires are limited to the load that can be carried with a maximuminflation pressure of 41 psi. An Extra Load or Light Load tire (for example, P235/75R15XL) will be brandedwith "Extra Load". A Standard Load tire does not bear any special designations.

European metric tires are either Standard or Reinforced Load. Standard Load tires are limited to the loadthat can be carried with a maximum inflation pressure that can range from 32 to 36 psi. Reinforced Loadtires are limited by the load t hat can be carried with a maximum inflation pressure of 42 psi. A Reinforcedtire (for example, 175/65R14RF) will be branded with "Reinforced". Standard Load tires do not bear anyspecial designations.

A standard load tire with a normal inflation pressure of 35 psi may be branded with a maximum inflation of

44 or 51 psi. An extra load tire with a normal inflation pressure of 41 psi may be branded with a maximuminflation of 50 psi. In both cases, the marking indicates the tires ability to meet special vehicle performancerequirements. It does not increase the tires load capacity.

Special DesignationsTPC Spec General Motors requires that the tires fitted on certain vehicles meet GMs own Tire Performance Criteria(TPC). These criteria are tested using performance formulas. When a tire meets the requirements, the TPCspecification number is branded on its sidewall.

M+S When any of the following markings appear on a tire, the tire meets the Rubber Manufacturers Association(RMA) definition of a mud and snow tire: M+S, M/S or M&S. In most cases, this marking identifies all-seasonperformance.

Severe Snow Marking When this mark appears on a tire in addition to the M&S marking, the tire meets the Rubber ManufacturersAssociation definition of a tire designed for use in severe snow conditions.U.S. Department of Transportation

Example: DOT M5H3 459X 065

The DOT marking signifies that the tire complies with United States Department of Transportation tire safetystandards and is approved for highway use. The first two characters following DOT designate t he tire's



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manufacturer and plant code. The third and fourth characters denote the tire size. The fifth, sixth, seventhand eighth (optional) characters identify the brand and other significant characteristics of the tire. The ninthand tenth characters denote the week the tire was produced. The final number signifies the year in which thetire was manufactured.For Michelin brand tires only, DOT markings for the week and year of production will have a triangle (

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