TIRE CODES (And there are a lot):

You have to know what the codes mean on your tires first. An example: Metric P185/80HR13 "P" = Passenger LT=Light Truck "185" = 185 cross sectional width in millimetres at the widest point of the tire bulge (Not the tread width at the road surface) To find Height (0.80 * 155 = 124 mm) "80" = Aspect Ratio (Height / cross sectional width)*100 An aspect ratio of 70 means the height of the tire is 70% as high as it is wide. The aspect ratio is related to the Load Carrying capability which is in the next example. The Load Carrying capability is related to the amount of air in the tire too. "H" = Speed Rated Code, Tells you the typical top speed rating of the tire.
L=120 km/h75 mph
M=130 km/h81 mph
N=140 km/h87 mph
P=150 km/h93 mph
Q=160 km/h99 mph
R=170 km/h106 mph
S=180 km/h112 mph
T=190 km/h118 mph
U=200 km/h124 mph
H=210 km/h130 mph
V=240 km/h149 mph
W=270 km/h168 mph
Y=300 km/h186 mph
ZR= >300 km/h186 mph

"R" = Type of Construction (R is for Radial) B=Belted For conventional tires, I don't think there is a letter. "13" = The diameter for the rim size (in inches this time). There is also a new code being used. eg. 205/60R15 82S 205 = 205 sectional width in millimetres 60 = Aspect Ratio (60% of 205 = 123 mm high sidewall) R = Type of Construction 15 = Diameter of rim in inches 82 = Load Index (The list of load indexes is further on) S = Speed Rating Index of 112 MPH certified by the manufacturer Each Company also puts on it's own codes such as 4S or +4 for all season or M+S for Mud and Snow. Easy to get confused here. THE DEPARTMENT OF TRANSPORT (DOT) CODE: DOT MA L9 ABC 0409 DOT is just that it meets DOT (Dept. of Transportation) specifications. MA is Manufacturer and plant code number. L9 is tire size and code number. ABC is a group of up to four symbols optional with manufacturer. 0409 is the date of manufacture. The last three numbers represent the week and year of manufacture. You should look for a "fresh" tire since time, moisture, heat, pollution and ultra violet light can effect your tires. Also make sure your tires have not been stored around gas or oil. examples: DOT 449 44= forty fourth week of the year, 9=1999 2006 - New U.S. DOT Tire Identification Number This begins with the letters DOT and indicates that the tire meets all federal standards. The next two numbers or letters are the plant code where it was manufactured, and the last four numbers represent the week and year the tire was built. For example, the numbers 2210 means the 22nd week of 2010. The other numbers are marketing codes used at the manufacturer’s discretion. TREADWEAR: This is based on 100. When you see Treadwear 440, this means the tire will wear 4.4 times normal. 260 means 2.6 times normal. Basically it is just a relative measure so you can compare tire wear. The treadwear grade is a comparative rating based on the wear rate of the tire when tested under carefully controlled conditions. For example, a tire graded 200 should have its useful tread last twice as long as a tire graded 100. However, real world tire tread life, in miles, depends on the actual conditions of their use. Tire life is affected by variations in driving habits, service practices...such as: tire rotation, wheel alignment and maintaining proper inflation pressure...and differences in road characteristics and climate. Most tires that have wear bars in the tread will indicate when 1/16 inch or less of tread is remaining. If you see these, it is strongly recommended that you change the tire. Another way of judging 0.0625 or 1/16 is to use a penny. On a USA penny 1/16 is roughly from the top of Abe Lincoln's head to the edge of the penny. TRACTION: The Traction code is a letter(s) AA= Very high, A=High, B=Medium, C=Low Traction grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on asphalt and concrete test surfaces. The traction grades from highest to lowest, are "AA", "A", "B" and "C". A tire graded "AA" may have relatively better traction performance than a tire graded "A", "B" or "C", based on straight ahead braking tests. The grades do not reflect the cornering or turning traction performance of the tires. TEMPERATURE: These codes are also A, B, and C from high to low. People who drive in the hot desert should buy "A" rated. Temperature grades represent the tire's resistance to heat and its ability to dissipate heat when tested under controlled laboratory test conditions. Sustained high temperature can cause the tire to degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure. The temperature grades from highest to lowest are "A", "B" and "C". The grade "C" corresponds to the minimum performance required by federal safety standard. Grades "B" and "A" represent higher levels of performance than the minimum required by law. The temperature grade is for a tire that is inflated properly and not overloaded. Excessive speed, underinflation or excessive loading, either separately on in combination, can cause heat build-up and possible tire failure. FIGURING OUT YOUR REPLACEMENT TIRE: Normally, your owner's manual recommends the type of tire for your car, or it is on a placard somewhere (glovebox for example). They say use only the same size and construction as originally installed and with the same or greater load capacity. (or words to that effect). But people do change their tire size and this is where my story really begins. You need to know what the manufacturer recommends and the vehicle capacity weight of your car. An example: P155SR13 P155/80R13 775lbs/tire for a '87 Toyota Tercel 5 door The air chamber determines the load capacity and there is a load index associated with the load capacity. The second number is the load capacity shown in "pounds" below. The first number is the "index" on the tire using the new code. 65=639 66=661 67=677 68=694 69=716 70=739 71=761 72=783 73=805 74=827 75=852 76=882 77=908 78=937 79=963 80=992 81=1019 82=1047 83=1074 84=1102 85=1135 86=1168 87=1201 88=1235 89=1279 90=1323 91=1356 92=1389 93=1433 94=1477 95=1521 96=1565 97=1609 98=1653 99=1709 100=1764 101=1819 102=1874 103=1929 104=1984 If you substitute, you must find the aspect ratio that matches or exceeds the load capacity recommended. So here is an example for P215/75R15 to P215/70R15: 6" /]-rim-[\-------- 6" / \ /]-rim-[\------------ ( 75 ) 161 mm ( 70 ) 150.5 mm \_________/________ \_______/ ___________ <---215---> <---215---> 1742 lbs max 1620 lbs max (Diagram not to scale, but you get the idea) Obviously, the air chamber is less and you can not substitute these tires. If you change the width of the tire, then the aspect ratio will also have to change to provide the same amount of air space. The following is my 2 cents on tire classification. Performance tires are - wide (thicker patch better in corners) - soft (stick to road whether wet or dry but wear out fast) - close tread (more road contact) Snow tires are - narrow (better to cut through snow) - wide open tread (snow clears out easier) Long Lasting tires - harder rubber compound (not as good traction) Any trade off between tires looses you something, either wet and dry performance, snow performance, or tire life. When buying tires ask for "fresh tires" and "long valve stems". The fresher the tires, the better, and long valve stems will make adding air easier. OK, now that you are an expert ;) go to
Safe Car Tire Guides

to pick out your tires!

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