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: 3.00-4, 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.
|16.9R24 Mitas RD-30||14.9-26 8PR SuperKing|
|280/85R20 Petlas TA110||480/80-26 Firestone STL|
|21X8.00-9Dunlop KT856||26X11R14 Carlisle R-14|
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|
|Speed symbol||Speed (km/h)||Speed (mph)||Speed symbol||Speed (km/h)||Speed (mph)|
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.
|Metric Size||Low Profile Options|
|95 Profile||85 Profile||Others||70 Profile||65 Profile||60 Profile||Others|