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How To Read Your Tire and Tyre Upsizing Calculator

 The sidewall of a car's tire has important information that tells you almost everything you need to know about it. The best way to understand tire markings is to break down the letters and numbers in an example.

Upsize calculator for your tyres

For our example, the numbers are:
P215/65R 15 95H

(P) Service Description
The service description may not always appear on the tire, but it is important to know how it can affect your vehicle. If there is a "P" on the sidewall, it stands for "passenger car." This refers to the U.S. (P-metric) method of tire sizing. "LT" stands for Light Truck, "ST" is for Special Trailer and "T" stands for Temporary, which is primarily used for small spare tires. If a tire does not have a "P" or another letter in front of the numbers, it is considered a "Euro-metric" tire. A Euro-metric tire conforms to the European tire specifications, and often carries a different load index than a comparably sized P-metric tire. We'll discuss load index in more detail below.

(215) Tire Width
The first number in this series refers to the tire's section width, or the distance from sidewall edge to sidewall edge, measured in millimeters up and over the tire's tread. Generally speaking, the larger this number is, the wider the tire will be.

(65) Aspect Ratio
This number is the tire's aspect ratio, or its section height compared to its section width. In this example, the section (or sidewall) height is 65 percent of the section width. This number can be indicative of a tire's purpose. Lower numbers, like 55 or less, mean a short sidewall for improved steering response and better overall handling.

(R) Internal Construction
The "R" refers to radial construction, which has been the industry standard in passenger-car tires for more than 25 years. Prior to radial tires, most cars came with bias-ply tires, which had a crude construction that made for poor handling. Bias-ply tires (which use a "B" for their description) are still used for certain truck applications.

(15) Rim Diameter
This is the wheel (or rim) diameter, in inches, for which the tire was sized. Pay particular attention to this number if you plan on upgrading your wheel size. If your wheel diameter changes, you'll have to purchase a new set of tires that matches this new diameter.

(95) Load Index
A tire's load index is a measurement of how much weight each tire is designed to support. The larger the number, the higher the load capacity. This is one of the most important numbers on your tire. To find out what "95" means, you have to look it up on a Load-Carrying Capacity Per Tire chart. Ninety-five indicates a maximum weight of 1,521 pounds. Remember that this is per tire, which means you have to multiply by four to get the total capacity for a complete set of tires. If the vehicle has its original tires, you can just refer to the doorjamb, which lists the maximum cargo capacity with passengers.

Some vehicles are equipped with "XL" tires. It doesn't mean that they're extra large, but it does mean that they are extra-load tires. The load index on these tires is much higher than a standard-load tire, which is why it is important to replace an XL tire with another XL tire.

Earlier, we discussed "P-metric" and "Euro-metric" sizing, and it's the difference in their load rating that can lead to confusion and potential trouble. For a given size, P-metric tires will have a load index that is one or two points lower than corresponding Euro-metric tires. So if your car came with Euro-metric tires, don't replace them with P-metric tires. You can, however, replace P-metric tires with equivalent-size Euro-metric ones because you gain load capacity that way.

Why is this important? Generally speaking, you don't want your replacement tires to have a lower load index number than the originals (again, as indicated by the driver's doorjamb or the owner's manual), particularly with high-capacity vehicles that ride on smallish tires, such as minivans.

Also, optional large-diameter wheels with lower-profile tires tend to have less load-carrying capacity because they contain less air. And it is the volume of air inside the tire, not the rubber itself or the wheel material that shoulders the load. The load index is especially important when shopping for a tire online, since some retailers do not specify whether a tire is P-metric or not.

(H) Speed Rating
The speed rating is a measurement of the speed at which the tire is designed to run for extended periods. An "H" speed rating signifies that this tire can be run safely at speeds of up to 130 mph for extended periods. Will it explode if it goes to 140? Not immediately. But it might, if it is run at that speed for an extended time.

Here is a complete list of the various tire speed ratings, and their associated letters:
S = 112 mph
T = 118 mph
U = 124 mph
H = 130 mph
V = 149 mph
*Z = Over 149 mph
*W = 168 mph
*Y = 186 mph
*(Y) = Over 186 mph

*The "Z" rating used to be the highest rating for tires having a maximum speed capability greater than 149 mph. But as tire technology improved, it ultimately split into the "W" and "Y" ratings. A "ZR" may sometimes appear in the size designation, as a sort of nod to the prior rating, but it will also be used in conjunction with a W or a Y. When a Y rating is enclosed in parentheses, it means that the tire is capable of speeds in excess of 186 mph.

Additional Information on Your Tires

DOT Code
The DOT code is used by the Department of Transportation (DOT) to track tire production for recall purposes. If a tire proves to be defective, this number helps keep track of where these tires ended up so buyers can be notified of the problem. At the end of the DOT code you'll find a four-digit number. This is the manufacturing date of the tire. The first two digits stand for the week; the other two are the year. For example, if your tire had "1613" listed, it was manufactured on the 16th week of 2013.

If you come across a three-digit number, you have a tire that was manufactured before 2000. A DOT tire code of "127" indicates the tire was made on the 12th week of the seventh year of the decade. But it's difficult to know whether that was 1997 or even 1987. According to, some tires produced in the 1990s may have a small triangle following the DOT number to identify the decade. But any tire that has a three-digit code is history. Tire experts recommend that you replace tires that are six or more years old, regardless of their tread depth.

Sometimes the DOT number will be located on the inside of the tire. In this case, you can either jack up the car to inspect it, or check with your local mechanic or tire shop. You should also make a habit of checking the manufacturing date on your spare tire as well.

Maximum Air Pressure
This number refers to the maximum amount of air you can put in a tire before you harm it. It is not the recommended tire pressure; that number can be found in your owner's manual and on the doorjamb.

Traction Rating
A traction rating can also be found on the sidewall of all modern tires. It can be represented as AA, A, B or C. This is a rating of a tire's traction when tested for straight-line braking on a wet surface. For this rating, AA signifies the best traction performance and C indicates the worst.

Temperature Rating
The temperature rating refers to the ability of the tire to withstand heat at high speeds. The ratings, from best to worst, are: A, B and C.

Treadwear Rating
Finally, you might find the word "TREADWEAR" on the sidewall followed by a number like 120 or 180. This is a rating of the tread's durability, as tested against an industry standard. The reference number is 100, so a tire with a treadwear rating of 200 has a predicted tread life that's twice as long as the industry standard, while a rating of 80 means a predicted tread life that's only 80 percent as long as the industry standard.

Standard load table (extract from ETRTO standards manual – 2010 page G7 - ref 42 psi (290 kPa)) 
60250 kg (550 lb)
80450 kg (990 lb)
100800 kg (1,800 lb)
1201,400 kg (3,100 lb)
61257 kg (567 lb)
81462 kg (1,019 lb)
101825 kg (1,819 lb)
1211,450 kg (3,200 lb)
62265 kg (584 lb)
82475 kg (1,047 lb)
102850 kg (1,870 lb)
1221,500 kg (3,300 lb)
63272 kg (600 lb)
83487 kg (1,074 lb)
103875 kg (1,929 lb)
1231,550 kg (3,420 lb)
64280 kg (620 lb)
84500 kg (1,100 lb)
104900 kg (2,000 lb)
1241,600 kg (3,500 lb)
65290 kg (640 lb)
85515 kg (1,135 lb)
105925 kg (2,039 lb)
1251,650 kg (3,640 lb)
66300 kg (660 lb)
86530 kg (1,170 lb)
106950 kg (2,090 lb)

67307 kg (677 lb)
87545 kg (1,202 lb)
107975 kg (2,150 lb)

68315 kg (694 lb)
88560 kg (1,230 lb)
1081,000 kg (2,200 lb)

69325 kg (717 lb)
89580 kg (1,280 lb)
1091,030 kg (2,270 lb)

70335 kg (739 lb)
90600 kg (1,300 lb)
1101,060 kg (2,340 lb)

71345 kg (761 lb)
91615 kg (1,356 lb)
1111,090 kg (2,400 lb)

72355 kg (783 lb)
92630 kg (1,390 lb)
1121,120 kg (2,470 lb)

73365 kg (805 lb)
93650 kg (1,430 lb)
1131,150 kg (2,540 lb)

74375 kg (827 lb)
94670 kg (1,480 lb)
1141,180 kg (2,600 lb)

75387 kg (853 lb)
95690 kg (1,520 lb)
1151,215 kg (2,679 lb)

76400 kg (880 lb)
96710 kg (1,570 lb)
1161,250 kg (2,760 lb)

77412 kg (908 lb)
97730 kg (1,610 lb)
1171,285 kg (2,833 lb)

78425 kg (937 lb)
98750 kg (1,650 lb)
1181,320 kg (2,910 lb)

79437 kg (963 lb)
99775 kg (1,709 lb)
1191,360 kg (3,000 lb)

Speed rating 

The speed symbol is made up of a single letter or an A with one number. It indicates the maximum speed at which the tire can carry a load corresponding to its Load Index. 
Speed rating 
Zover 149over 240
(W)over 168over 270
(Y)over 186over 300
Car / SUV / Van / Light Truck Tire Calculator (P-metric) 
SIX EASY STEPS! ( For calculation purposes P205/65R15, LT205/65-15 and 205/65R15 are the same. )
Manufacturer's Suggested Tire Size *

1 Select the tire Width in MM (Inches) 

2 Select the Aspect Ratio (tire height/width) 

3 Select the Rim Diameter in inches 

Overall Wheel diameter in Inches
Wheel Circumference in Inches
Wheel revolutions per mile
Wheel revolutions per second @ 65MPH
ALTERNATE or Desired Tire Size *

4 Select new tire Width in MM (Inches) 

5 Select new tire Aspect Ratio (tire height/width) 

6 Select new Rim Diameter in inches 

Overall Wheel diameter in Inches
Wheel Circumference in Inches
Wheel revolutions per mile
Wheel revolutions per second @ 65MPH
NOTE: Changing the tire diameter CHANGES the SPEEDOMETER accuracy!

This ALTERNATE tire size will cause the 'Actual Vehicle Speed' to be
 mph, when the speedometer reads exactly 65mph.Or, when the 'Actual Vehicle Speed' is 65mph the speedometer will now read Also, the ground clearance of the vehicle will change by  inches.

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