Tyre Finder & Size Guide


Use our TYRE FINDER TOOL to search through our range and return to you all the tyres matching the size you require.

Step 1)  Most common sizes can be found in the 'POPULAR SIZES' drop down list, select your size and CLICK 'GO'!
Step 2)  If your size isn't listed, then manually enter the tyres 'section width', 'construction' and 'rim size'. You can optionally enter the tyres 'profile' or 'outer diameter' markings if either is included in your tyres size marking. Click 'FIND TYRES!'.

TYRE FINDER: CHECK POPULAR SIZES!
 
SECTION WIDTH:
CONSTRUCTION:
RIM SIZE:  
OPTIONAL: Only provide these if specified by your tyre marking!
OUTER DIAMETER:
PROFILE:       
OR ENTER SIZE MANUALLY
 
TUBE FINDER:
RIM SIZE:
VALVE:




Understanding Your Tyre Size

Understanding these sizes and searching for the size you need can be a tricky business. This guide aims to help you understand tyre size markings to ensure that you get your tyre search right.

Reading Your Tyre Size - Rim/Section Width/Profile/Outer Diameter

There are several methods for giving the size of tyres, with measurements sometimes given in inches, sometimes in millimetres, or sometimes in both! The examples and explanations given below should hopefully make it possible for you to recognise your own size markings.

Example 1:  3.00-4,  3.50-6,  4.00-8,  5.20-10,  6.00-12...
The first number i.e. 3.00, tells you the width of the tyre (called the SECTION WIDTH). It also tells you the height of the sidewall of the tyre in inches. The '-' means the tyre is CROSSPLY (Radial construction would be represented by an 'R'). The final number, 4, is the RIM SIZE in inches. So a 3.00-4 tyre would fit on a 4 inch rim/wheel, have a 3 inch section width and be of Crossply construction.

Example 2:  6-12,  7-14,  8-16,  9.5-18
Same as the above but it does away with the '.00' for the first part of the size. Again, all dimensions are in inches. It is important to note that tyres with very similar markings may not be compatible - a 6-12 tyre will be significantly different in size to a 6.00-12. If in doubt, stick to the exact size that is fitted to the vehicle or recommended by the manufacturer or ask the Big Tyres Team for help.

Example 3:  4.10/3.50-4,  4.10/3.50-6,  5.30/4.50-6
Here we have four parts to the tyre marking. The first, 4.10, is the width (SECTION WIDTH) of the tyre. The second, 3.50, is the height of the sidewall, the third number is the rim/wheel diameter (RIM SIZE), and again the '-' tells us its of CROSSPLY construction (Radial construction would be represented by an 'R'). So a 4.10/3.50-4 tyre is 4.1 inches wide (section width of 4.1"), has 3.5 inch tall sidewalls, fits a 4 inch wheel/rim and is of crossply construction.

Example 4:  11X4.00-4,  13X5.00-6,  18X8.50-8,  25X12.00-9
The first part is the OUTER DIAMETER of the tyre (the overall height from the ground to the top of the tyre) in inches. The second part is the width of the tyre (SECTION WIDTH) in inches, and the third part is the rim diameter (RIM SIZE) in inches. The '-' tells us its of CROSSPLY construction. So a 25X12.00-9 ATV tyre would be 25 inches tall (25" outer diameter), 12 inches wide (12" section width) and fit a 9" wheel/rim.

Example 5:  10X3,  18X4,  260X85
This marking is becoming obsolete, but you may still have tyres marked in this way. Measurements can be in inches or millimetres (it's fairly obvious which is which). The first part is the overall tyre height (OUTER DIAMTER), the second is the tyre width (SECTION WIDTH). The rim diameter is not mentioned in this size marking, but it can be easily worked out, because the tyre sidewall height will be the same as the tyres width. So, an 18x4 tyre is 18" tall (outer diameter), 4" wide (section width), and fits a 10" diameter rim (18" overall height minus two lots of 4" high sidewalls). The modern equivalent size for an 18x4 would therefore be 4.00-10. A 260x85 tyre would be 260mm high and 85mm wide. Converting these dimensions to inches gives us a tyre 10" high, 3" wide on a 4" rim. The modern equivalent size would be a 3.00-4.

Example 6:  255/60-10,  195/50R13, 420/85R28
The first part is the width (SECTION WIDTH) of the tyre in mm, the second part, is the PROFILE of the tyre (height of the sidewall expressed as a percentage of the width), and the third number is the rim diameter (RIM SIZE) in inches. The 'R' when present within the size, means the tyre is of RADIAL construction, whereas the '-' shows its of CROSSPLY construction. So a 420/85R28 is 420mm wide (SECTION WIDTH), has a PROFILE of 85% (side walls are 85% of 420mm = 357mm tall), is of RADIAL construction and fits a 28 inch rim (RIM SIZE is 28"). A 195/50R13 tyre would be 195mm wide, have a sidewall height of 98mm, fit a 13" rim/wheel and be radial construction.

It is becoming more common for ATV/Quad tyres to be marked up in this manner. They are usually dual marked with their traditional inch dimensions also, but with a calculator, it's possible to convert from one to the other. For example, a 255/60-10 ATV tyre would be 255mm wide, have a 153mm sidewall height and fit a 10" rim. Converting these dimensions to inches would give us 10" width, 6" sidewall height and 22" overall height (10" rim plus two lots of 6" high sidewalls). In traditional ATV tyre size marking, this would become a 22x10.00-10.

Example 7:  145R10,  155R12 
The first part is the width (SECTION WIDTH) of the tyre in mm,  and the second number is the wheel/rim diameter (RIM SIZE) in inches. The 'R' means its of RADIAL construction, whereas a '-' instead would mean its CROSSPLY. There is no profile number percentage indication included in the tyre size, but with this type of marking the tyre sidewall height is normally taken to be 80% of the tyre width. So its assumed the profile is 80. You may sometimes see a tyre with the 80% in the size too eg. 155/80-13.

So, a 145R10 is a radial tyre, 145mm wide, sidewall height of 116mm (80% of 145mm) and fits a 10" rim/wheel. The approximate overall height of the tyre can be worked out by converting both dimensions to either mm or inches, and adding the rim diameter to twice the sidewall height.

Visual Examples

16.9R24 Mitas RD-3014.9-26 8PR SuperKing
tyre sizetyre size


280/85R20 Petlas TA110480/80-26 Firestone STL
tractor tyre markingtyre size


21X8.00-9Dunlop KT85626X11R14 Carlisle R-14
tyre sizetyre size


Load index and Speed Rating

The load index is a number that indicates the load or weight a tyre can take. The chart below shows common values. The speed index is given by a letter (or letter and number in the case of 'A' speed rating) between A and Z and represents the top speed at which the tyre can be used.



Load index kg
Load index kg
Load index kg
Load index kg

0 45
40 140
80 450
120 1400

1 46.2
41 145
81 462
121 1450

2 47.5
42 150
82 475
122 1500

3 48.7
43 155
83 487
123 1550

4 50
44 160
84 500
124 1600

5 51.5
45 165
85 515
125 1650

6 53
46 170
86 530
126 1700

7 54.5
47 175
87 545
127 1750

8 56
48 180
88 560
128 1800

9 58
49 185
89 580
129 1850

10 60
50 190
90 600
130 1900

11 61.5
51 195
91 615
131 1950

12 63
52 200
92 630
132 2000

13 65
53 206
93 650
133 2060

14 67
54 212
94 670
134 2120

15 69
55 218
95 690
135 2180

16 71
56 224
96 710
136 2240

17 73
57 230
97 730
137 2300

18 75
58 236
98 750
138 2360

19 77.5
59 243
99 775
139 2430

20 80
60 250
100 800
140 2500

21 82.5
61 257
101 825
141 2575

22 85
62 265
102 850
142 2650

23 87.5
63 272
103 875
143 2725

24 90
64 280
104 900
144 2800

25 92.5
65 290
105 925
145 2900

26 95
66 300
106 950
146 3000

27 97
67 307
107 975
147 3075

28 100
68 315
108 1000
148 3150

29 103
69 325
109 1030
149 3250

30 106
70 335
110 1060
150 3350

31 109
71 345
111 1090
151 3450

32 112
72 355
112 1120
152 3550

33 115
73 365
113 1150
153 3650

34 118
74 375
114 1180
154 3750

35 121
75 387
115 1215
155 3875

36 125
76 400
116 1250
156 4000

37 128
77 412
117 1285
157 4125

38 132
78 425
118 1320
158 4250

39 136
79 437
119 1360
159 4375


Speed symbol Speed (km/h) Speed (mph)
Speed symbol Speed (km/h) Speed (mph)
A1 5 3
K 110 68
A2 10 6
L 120 74
A3 15 9
M 130 81
A4 20 12
N 140 87
A5 25 16
P 150 94
A6 30 19
Q 160 100
A7 35 22
R 170 106
A8 40 25
S 180 112
B 50 31
T 190 118
C 60 37
U 200 124
D 65 40
H 210 130
E 70 43
V 240 149
F 80 50
Z 240+ 149+
G 90 56
W 270 168
J 100 62
Y 300 188

Imperial to Metric Conversion Chart Including Low Profile Options

Tyre sizes are listed in either imperial form or metric form. Some times these sizes are interchangable, or sometimes the older imperial format will now have been replaced with the newer metric equivalent. You should try using both the metric and imperial version of your tyre size in your search if you're unsure which is correct/current. Radial tyres are now more commonly marked in metric sizes. The chart below shows how to convert your imperial tyre size into its metric equivalent.

Rim
Size
Imperial
Size
Metric Size Low Profile Options
95 Profile 85 Profile Others 70 Profile 65 Profile 60 Profile Others
20" 9.5-20

260/80R20 300/70R20 340/65R20


11.2-20
280/85R20
320/70R20



12.4-20
320/85R20
360/70R20 420/65R20


13.6-20
340/85R20













24" 9.5-24
250/85R24





11.2-24
280/85R24





12.4-24
320/85R24





13.6-24
340/85R24
380/70R24 440/65R24 480/60R24

14.9-24
380/85R24
420/70R24 480/65R24


16.9-24
420/85R24
480/70R24 540/65R24


17.5L-24

440/70R24




17.5L-24

445/70R24




17.5L-24

460/70R24




19.5L-24

495/70R24




19.5L-24

500/70R24












26" 16.9-26
420/85R26
480/70R26 540/65R26


18.4-26

480/80-26 520/70R26



23.1-26

620/75R26
750/65R26


28.1/28L-26

750/65R26












28" 9.5-28
250/85R28





11.2-28
280/85R28
320/70R28



12.4-28
320/85R28
360/70R28 420/65R28


13.6-28
340/85R28
380/70R28 440/65R28 480/60R28

14.9-28
380/85R28
420/70R28 480/65R28 520/60R28

16.9-28
420/85R28 440/80-28 480/70R28 540/65R28 600/60R28

19.5L-28

495/70R28












30" 14.9-30
380/85R30
420/70R30



16.9-30
420/85R30
480/70R30 540/65R30 600/60R30

18.4-30
460/85R30
520/70R30 600/65R30
710/55R30

23.1-30

620/75R30 650/70R30











32" 8.3-32 210/95R32






9.5-32 230/95R32
270/80R32




11.2-32 270/95R32






12.4-32
320/85R32 300/80R32




24.5-32

650/75R32 680/70R32



30.5L-32

800/65R32


900/55R32

30.5L-32





1000/50R32









34" 14.9-34
380/85R34





16.9-34
420/85R34
480/70R34 540/65R34


18.4-34
460/85R34
520/70R34 600/65R34










36" 8.3-36 210/95R36






9.5-36 230/95R36
270/80R36




11.2-36 270/95R36






12.4-36
320/85R36





13.6-36
340/85R36













38" 9.5-38 230/95R38






11.2-38 270/95R38






12.4-38
320/85R38





13.6-38
340/85R38





14.9-38
380/85R38





16.9-38
420/85R38
480/70R38 540/65R38 600/60R38

18.4-38
460/85R38
520/70R38 600/65R38 650/60R38

20.8-38
520/85R38
580/70R38 650/65R38 710/60R38









40" 7.2-40 180/95R40






9.5-40 230/95R40














42" 9.5-42 230/95R42






12.4-42 300/95R42






16.9-42
420/85R42





18.4-42
460/85R42

600/65R42


20.8-42
520/85R42
580/70R42 650/65R42 710/60R42 900/50R42









44" 8.3-44 210/95R44






9.5-44 230/95R44






11.2-44 270/95R44














46" 12.4-46 300/95R46






14.9-46
380/85R46





18.4-46
460/85R46





20.8-46
520/85R46
620/70R46











48" 9.5-48 230/95R48






11.2-48 270/95R48






13.6-48
340/85R48













52" 12.4-52 300/95R52














54" 11.2-54 270/95R54






12.4-54 320/90R54






 

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