How to read Tire sidewall writing

[Shifty Powers]

This is a very simple process for those trying to decipher the numbers and letters on your tires. Most importantly, your overall tire height. This is helpful if you want to upgrade your rim size and keep the same overall dimensions or for calculation of gear needs.

For this example, we're going to use the sample tire size P215/50R17 91V

The first character, usually P, LT, or T stand for the type of vehicle this tire has been engineered for.
P for passenger car
LT for light truck
T for temporary
etc, etc
If there is no indication of a character, then the tire has been manufacturer in accordance with European Standards

Common tire sizes are broken down into three parts
First Number: Tread Width, usually in millimeters (215)
Second Number: Sidewall Ratio of tread width to sidewall height (50)
In this example, the side wall is 50% of the tread width

Sidewall height = Tread width * Sidewall Ratio
Sidewall height = 215mm * 50%
(when multiplying a percentage, use a decimal to signify the percent of the value we are multiplying. In our case, use .50)
Sidewall height = 107.5mm

To convert this number to inches, multiply the Sidewall height by .03937
107.5mm * .03937 = 4.23in
Third Number: Wheel Diameter (R17) The R in the third number stands for a Radial Tire.

Now, In order to determine total tire height, Multiple the sidewall height by 2 (to account for the top and bottom sidewall) and then add the rim diameter4.23in + 4.23in + 17in = 25.46in

The next part I copied from another site as it explains it best

"The second part of the number is the service description. Written here as 91V, this tells us two things.
First, 91 indicates the tire's load index. This is an assigned numerical value used to compare the relative load-carrying capabilities of any given tire. In general, higher numbers indicate greater load carrying capacities.
A standard conversion table is used to decode the maximum load for any given tire. The scale starts at 50 (418.8 pounds) and goes up in single increments to 124 (3,527.5 pounds) though most modern passenger cars and light trucks fall somewhere between 70 and 110. In our example, this tire can be loaded with up to 1,356 pounds.
Second, and just as important, is the speed rating for this tire. This is also an assigned value system. In this case, V indicates this tire is approved for speeds up to 149 mph."

Rating

M​

N​

P​

Q​

R​

S​

T​

U​

H​

V​

W​

Y​

Z​

Max. MPH

81​

87​

93​

99​

106​

112​

118​

124​

130​

149​

168​

186​

>149​

Max. KM/H

130​

140​

150​

160​

170​

180​

190​

200​

210​

240​

270​

300​

>240​

 

[Shifty Powers]

When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.

W	168 mph	270 km/h	Exotic Sports Cars
Y	186 mph	300 km/h	Exotic Sports Cars

While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.

225/50ZR16	in excess of 149 mph, 240 km/h
205/45ZR17 88W	168 mph, 270 km/h
285/35ZR19 99Y	186 mph, 300 km/h

Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:

285/35ZR19 99Y	186 mph, 300 km/h
285/35ZR19 (99Y)	in excess of 186 mph, 300 km/h

As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tires capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.

More Tire Tech Information

Related Links:
Calculating Approximate Tire Dimensions
Contact Patch
Plus Size Wheels and Tires
Tire Size Conversion Chart
Tire Size Guide
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In the tire industry, there are certain abbreviations that are used frequently and often those of us in the business forget that not everyone we talk to knows what all of the jargon means.

For example O.E. stands for Original Equipment and Ser. Des. means service description.

Other abbreviations associated with tires include:

• PSI = pounds per square inch
• AS = all-season
• M+S = mud and snow
• SL = standard load
• ASY = asymetrical tread design
• ZR = Z speed rating (149+) and radial construction
• TPMS = tire pressure monitor system
• WS = white sidewall stripe

The list can go on on from here, but these are some of the more common abbreviations used in the tire industry.

• ROF = run on flat
  
• RF = reinforced sidewall
• OWL = outlined white letter
• UTQG = uniform tire quality grade
• OD = overall diameter
• Snowflake M+S = severe duty mud and snow

 

[Shifty Powers]

Also For the DOT # on the tire

or example your DOT Number might read " WYX4 HJY (2712) " The only part that matters is the end of the DOT that tells you that the tire was made on the 27th week of 2012. So if you come across a tire with a DOT number of (2405) That tire is no longer any good and shouldn't even been on the road.