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!'.


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: 3.004, 3.506, 4.008, 5.2010, 6.0012...
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 3.004 tyre would fit on a 4 inch rim/wheel, have a 3 inch section width and be of Crossply construction.
Example 2: 612, 714, 816, 9.518
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 612 tyre will be significantly different in size to a 6.0012. 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: 4.10/3.504, 4.10/3.506, 5.30/4.506
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 4.10/3.504 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: 11X4.004, 13X5.006, 18X8.508, 25X12.009
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 25X12.009 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 4.0010. 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 3.004.
Example 6: 255/6010, 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 255/6010 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 22x10.0010.
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. 155/8013.
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 RD30  14.926 8PR SuperKing 
280/85R20 Petlas TA110  480/8026 Firestone STL 
21X8.009Dunlop KT856  26X11R14 Carlisle R14 
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"  9.520  260/80R20  300/70R20  340/65R20  
11.220  280/85R20  320/70R20  
12.420  320/85R20  360/70R20  420/65R20  
13.620  340/85R20  
24"  9.524  250/85R24  
11.224  280/85R24  
12.424  320/85R24  
13.624  340/85R24  380/70R24  440/65R24  480/60R24  
14.924  380/85R24  420/70R24  480/65R24  
16.924  420/85R24  480/70R24  540/65R24  
17.5L24  440/70R24  
17.5L24  445/70R24  
17.5L24  460/70R24  
19.5L24  495/70R24  
19.5L24  500/70R24  
26"  16.926  420/85R26  480/70R26  540/65R26  
18.426  480/8026  520/70R26  
23.126  620/75R26  750/65R26  
28.1/28L26  750/65R26  
28"  9.528  250/85R28  
11.228  280/85R28  320/70R28  
12.428  320/85R28  360/70R28  420/65R28  
13.628  340/85R28  380/70R28  440/65R28  480/60R28  
14.928  380/85R28  420/70R28  480/65R28  520/60R28  
16.928  420/85R28  440/8028  480/70R28  540/65R28  600/60R28  
19.5L28  495/70R28  
30"  14.930  380/85R30  420/70R30  
16.930  420/85R30  480/70R30  540/65R30  600/60R30  
18.430  460/85R30  520/70R30  600/65R30  710/55R30  
23.130  620/75R30  650/70R30  
32"  8.332  210/95R32  
9.532  230/95R32  270/80R32  
11.232  270/95R32  
12.432  320/85R32  300/80R32  
24.532  650/75R32  680/70R32  
30.5L32  800/65R32  900/55R32  
30.5L32  1000/50R32  
34"  14.934  380/85R34  
16.934  420/85R34  480/70R34  540/65R34  
18.434  460/85R34  520/70R34  600/65R34  
36"  8.336  210/95R36  
9.536  230/95R36  270/80R36  
11.236  270/95R36  
12.436  320/85R36  
13.636  340/85R36  
38"  9.538  230/95R38  
11.238  270/95R38  
12.438  320/85R38  
13.638  340/85R38  
14.938  380/85R38  
16.938  420/85R38  480/70R38  540/65R38  600/60R38  
18.438  460/85R38  520/70R38  600/65R38  650/60R38  
20.838  520/85R38  580/70R38  650/65R38  710/60R38  
40"  7.240  180/95R40  
9.540  230/95R40  
42"  9.542  230/95R42  
12.442  300/95R42  
16.942  420/85R42  
18.442  460/85R42  600/65R42  
20.842  520/85R42  580/70R42  650/65R42  710/60R42  900/50R42  
44"  8.344  210/95R44  
9.544  230/95R44  
11.244  270/95R44  
46"  12.446  300/95R46  
14.946  380/85R46  
18.446  460/85R46  
20.846  520/85R46  620/70R46  
48"  9.548  230/95R48  
11.248  270/95R48  
13.648  340/85R48  
52"  12.452  300/95R52  
54"  11.254  270/95R54  
12.454  320/90R54 