What fits best, Weights & Sizes
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By dogfight
#21616 The meaning of tire codes

Tire identification diagram
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Tire identification diagram, light truck specific features
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The tire code consists of a string of letters and numbers, as follows:

An optional letter (or letters) indicating the intended use or vehicle class for the tire
'P' - Passenger
'LT' - Light Truck
'ST' - Special Trailer
'T' - Temporary
The width of the tire - in millimeters, from sidewall edge to sidewall edge.
A slash character ('/').
The ratio of the sidewall height to the total width of the tire - as a percentage. If this is missing, it is assumed to be 82%. If the number is larger than 200, then this is the diameter of the entire tire in millimeters.
Construction of the fabric of the tire
'B' - bias belt
'D' - diagonal
'R' - radial
Diameter of the rim that this tire is designed to fit - in inches.
Load index.
Speed rating - one or perhaps two letters (see table below).


Load Index
Load Index Code Pounds Kilograms Code Pounds Kilograms
71 761 345 91 1,356 615
72 783 355 92 1,389 630
73 805 365 93 1,433 650
74 827 375 94 1,477 670
75 853 387 95 1,521 690
76 882 400 96 1,565 710
77 908 412 97 1,609 730
78 937 425 98 1,653 750
79 963 437 99 1,709 775
80 992 450 100 1,764 800
81 1,019 462 101 1,819 825
82 1,047 475 102 1,874 850
83 1,074 487 103 1,929 875
84 1,102 500 104 1,984 900
85 1,135 515 105 2,039 925
86 1,168 530 106 2,094 950
87 1,201 545 107 2,149 975
88 1,235 560 108 2,205 1,000
89 1,279 580 109 2,271 1,030
90 1,323 600 110 2,337 1,060


Speed rating codes
The code is made up of one or two letters describing the maximum safe speed for the tire.

Tire speed rating codes
Code MPH km/h
N 93 150
Q 99 160
R 105 170
S 112 180
T 118 190
U 124 200
H 130 210
V 149 240
W 167 270
Y 186 300
ZR Over 149 Over 240

The code "ZR" means a speed limit for the tire of more than 240 km/h. In this case there is often an additional code, example: 225/45 ZR 17 Y.


Additional marks
There are numerous other markings on a typical tire, these may include:

M&S: On winter tires, at the end of the above mentioned codes the following abbreviation can be found: M&S for Mud and Snow. On spike tires there is an additional E after the S.

E4 - Tire approved according ECE-regulations, (the number indicates the country of approval).
030908 - Approval number of the tire

DOT code: All tires imported into the USA have the DOT code, as required by the Department of Transportation (DOT). It specifies the company & factory, mold, batch, and date of production (2 digits for week of the year plus 2 digits for year; or 2 digits for week of the year plus 1 digit for year for tires made prior to 2000)

TL - Tubeless

TT - Tubetype, tire with an inner-tube

Made in - Country of production

C (commercial) - Tires for light trucks (Example: 185 R14 C)

B - Bias Belted tires for motorcycles (Example: 150/70 B 17 69 H)=diagonal construction with belt added under the tread

SFI - abbr. for "side facing inwards" = inside of asymmetric tires

SFO - abbr. for "side facing outwards" = outside of asymmetric tires

TWI - Tire wear index, an indicator in the main tire profile which shows when the tire is worn down and needs to be replaced

SL (standard load): Tire for normal usage and loads

XL (extra load): Tire for heavy loads

rf - Reinforced tires

Arrows - Some tread designs are designed to perform better when driven in a specific direction (clockwise or counter-clockwise). Such tires will have an arrow showing which way the tire should rotate when the vehicle is moving forwards. It is important not to put a 'clockwise' tire on the left hand side of the car or a 'counter-clockwise' tire on the right side.

Tire geometry
When referring to the purely geometrical data, a shortened form of the full notation is used. To take a common example, 195/55R16 would mean that the width of the tire is 195 mm at the widest point, the height of the side-wall of the tire is 55% of the width (107 mm in this example) and that the tire fits 16 inch diameter wheels.

Less commonly used in the USA and Europe (but often in Japan for example) is a notation that indicates the full tire diameter instead of the side-wall height. To take the same example, a 16 inch wheel would have a diameter of 406 mm. Adding twice the tire height (2x107 mm) makes a total 620 mm tire diameter. Hence, a 195/55R16 tire might alternatively be labelled 195/620R16.

Whilst this is theoretically ambiguous, in practice these two notations may easily be distinguished because the height of the side-wall of an automotive tire is typically much less than the width. Hence when the height is expressed a percentage of the width, it is almost always less than 100% (and certainly less than 200%). Conversely, vehicle tire diameters are always larger than 200 mm. Therefore, if the second number is more than 200, then it is almost certain the Japanese notation is being used - if it's less than 200 then the US/European notation is being used.


Example
The tires on a MINI Cooper might be labelled:

P195/55R16 85H

'P' these tires are for a passenger vehicle.
195 - the width of the tire is 195 mm at the widest point.
55 - indicates that the height of the side-wall of the tire is 55% of the width - 107 mm.
R - this is a radial tire.
16 - this tire fits 16 inch diameter wheels.
85 - the load index, a maximum of 515 kg per wheel in this case.
H - the speed index, this means the maximum permitted speed, here 210 km/h (130 mph).
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By ohDirka
#21618 some good info here, wish i had this like 6 months ago
By BlueVic_8354
#215973 its really nice to know these things when one is looking around for tires...