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Determining the Size of Tyres on Your Car

Sidewall Markings

Look at the sidewall of your tyre and you'll notice different markings and codes. One of them represents your tyre's size.

Tyre Sizes

Various numbers and letters are joined together to show the tyre size. For example - 205/55 R16 82 H.
What does it mean?

  • 205 - Width of the tyre in milimetres.
  • 55 - The ratio of the tyre's height to the tyre's width, expressed in percentages, popularly known as the aspect ratio.
  • R - Tyre's construction type - in this instance, RADIAL. If your tyre doesn't have an "R" but rather "A", "B", or "X", we're talking about bias ply construction.
  • 16 - Rim diameter in inches.
  • 82 - Load Index, or how much weight can the tyre handle.
  • H - Speed Rating, or how fast is too fast for the tyre.

This is all the basic information for an educated tyre purchase. If you want to delve deeper into the "writings on the wall", do refer to the information below.

Aspect Ratio

Aspect ratio, or profile helps us determine what percentage of tyre's width goes into the height of its sidewall. The bigger the percentage, the bigger the driving comfort but at the expense of handling properties. It's usual for buses and trucks to have high aspect ratios (up to 95% of tyre's width!). Sports vehicles, on the other hand, have extremely low aspect ratios. You must have heard about the low-profile tyres before. Their sidewalls are rather short (up to 30% of tyre's width), which brings about sport-grade handling at the expense of driving comfort. Much of the vibrations gets passed on to the suspension. One of the reason race cars have upgraded suspension systems.

Speed Ratings

Every tyre has its speed limit, depicted by a certain letter. For the most part, the higher up the alphabet scale the letter is, the faster your tyre can run, with two exceptions to the rule. Consult the table to see what we mean.


Speed symbol

Max speed mph

Max. speed km/h
N 87 140
P 93 150
Q 99 160
R 106 170
S 112 180
T 118 190
H 130 210
V(and ZR*) 149 240
W 168 270
Y 186 300

*ZR marking was used before 1990s to mark the high-performace tyres.

Load Index

The last two-digit number denotes the tyre's maximum load capacity when reaching its speed rating limit.

Load Index kg
64 280
65 290
66 300
67 307
68 315
69 325
70 335
71 345
72 355
73 365
74 375
75 387
76 400
77 412
78 425
79 437
80 450
81 462
82 475
83 487
84 500
85 515
86 530
87 545
88 560
89 580
90 600
91 615
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Load Index kg
92 630
93 650
94 670
95 690
96 710
97 730
98 750
99 775
100 800
101 825
102 850
103 875
104 900
105 925
106 950
107 975
108 1000
109 1030
110 1060
111 1100
112 1120
113 1150
114 1180
115 1215
116 1250
117 1285
118 1320
119 1360

DOT code

DOT is the abbreviation for Department of Transportation and it's comprised of the tyre factory code and the production date. The factory codes are too cumbersome to explain in this post and aren't as important as the production date code.

Tyre Age

If you're asking yourself "how old are my tyres?", look for either a three-digit number or a four-digit number on the tyre sidewall. Three-digit numbers represent tyres made before 2000, four-digit ones the tyres made after 2000. If you're on the south side of 2000, you definitely need a tyre change. And not only then. Generally, if the tyre is older than ten years, it should be replaced, even if the tread depth is within bounds. Production year of your tyre is represented by the last two digits. The first two digits represent the production week.

Other Tyre Markings

  • M+S - Stands for tyres capable of helping you drive through mud and snow.
  • Three-Peaked Mountain and Snowflake Symbol (Alpine Symbol) - Stands for tyres built to withstand and trump the horrors of sub-zero temperatures and icy roads.
  • E-Mark - Stands as a proof that the tyre is within EU or International (UNECE) standards regarding its dimensions, load index, speed rating, as well as having an adequate tread depth.