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Bicycle tyres come in a wide range of different sizes, it is important to understand a little bit about the tyre size you use when purchasing new tyres or tubes to fit.
Bicycle tyre sizing has a long history of confusing measurements, names, decimals and fractions. First we will go over how the sizing works, some of the most common sizes you'll find on modern bikes today and then we'll try to decipher some of the older 'obsolete' sizes (mostly useful if you're restoring a classic bike or have older wheels on your bike).
Tyre Sizing Systems
First some history - Back before any standardization of bicycle tyre sizes different measurements and ways of measuring were developed by each country that produced bikes. This lead to tyres of the same size being refered to by diferent numbers in different countries or tyres that had the same size markings but were different and wouldnt fit the same size rim.
This is a brief (believe it or not) rundown of the tyre sizing specifications you'll see around. If you dont want or need to know the specifics feel free to skip ahead to 'Tyre Sizing in General'.
ISO, E.T.R.T.O System & BSD Tyre Sizing
Here's where the confusion starts; believe it or not all of these things are the same. This is the modern system for sizing and manufacturing tyres. ISO is the International Organization for Standardization; The standard they use was developed by E.T.R.T.O, the European Tyre and Rim Technical Organisation. BSD will be explained.
The ISO system uses two numbers, here are some examples: 559 x 44 and 622 x 23. These may look unfamiliar to you which is fair enough. Although the ISO system is the standard which can be accurately measured and is the standard by which modern tyres are manufactured, the tyres are not often referred to by their ISO measurements. These sizes refer to the BSD (the larger number) meaning 'Bead Seat Diameter' which refers to the diameter (in millimetres) of the bead of the tyre or the outer part of the rim where the bead hooks into. The smaller number is the tyre width in millimetres. 559 x 44 is referred to as a 26 x 1.75" and the 622 x 23 is referred to as 700c x 23 - This will be explained as we go through the other tyre sizing systems.
French Tyre Sizing
French tyre sizing is an old system which is still used but the size designations are really only reference points in modern tyre sizing.
The most common modern French tyre size being 700c. 700c today isnt what it used to be; 700 referred to the nominal diameter of the tyre in mm and the letter code referred to the width - 'A' being narrow, 'D' being wide. Tyres came in various other diameters from 400 up to 700mm, all with width letter codes from A to D. The only other French sizes you might see around on modern bikes is 650c (571mm ISO/BSD) which has been used for small sized road bikes & triathlon/time trial bikes and 650b (584mm ISO/BSD) which, at the time of writing, is emerging as a new mountain bike tyre size.
Today when you see the most common French tyre size; 700c, this actually refers only to the 622mm Bead seat diameter (or ISO) size of original 700c tyres and has nothing to do with the width. 700c tyres are used on road bikes and most forms of hybrid road bikes.
Decimal Tyre Sizing
Decimal tyre sizes in inches are commonly used for basically all bike tyre sizes today except for road racing tyres. Mountain bike tyres are marked 26" x 1" up to 3". 26" being a rough outer diameter of the installed and inflated tyre and referring to the 559mm ISO/BSD size and the second number being the tyre width. A point of confusion with decimal sizes is with what could be called 28", 29" or even the French 700c - As long as they don't use fractions and only decimal measurements these all refer to a 622mm ISO/BSD and are actually made to fit the same size rim. Generally 700c is used for road racing tyres and 622mm ISO/BSD size tyres from 19mm, up to around 28mm width. Beyond that width the terms 700c and 28" are interchangeable. Once tyres get above 47mm or 1.8" in width with a 622mm ISO/BSD they're usually called 29" - All you need to remember is that these are only references to tyre size and rough outer diameter - if you're unsure check the ISO measurement.
Fractional or British Tyre Sizing
Fractional tyre sizing can be quite confusing as modern europan tyre manufacturers still put fractional sizes on their tyres - our advice is to ignore this if you can and use the french or ISO sizes that should be printed on the tyre instead.
For the purposes of modern bicycle tyres fractonal sizes are obsolete. The only traditional fractional size still in use is 12 1/2" diameter tyres that are used on kids' bikes, scooters and buggies.
To quote Sheldon Brown and the 'Brown's Law of Tire(tyre) Sizing':
"If two tires are marked with sizes that are mathematically equal,but one is expressed as a decimal and the other as a fraction,these two tires will not be interchangeable."
Here is an example of the difference between decimal and fractional tyre sizing: 26 x 1.75" and 26 x 1 3/4" - these numbers seem to be the same when the fraction is converted to a decimal but the 26 x 1.75" tyre has a BSD of 622mm and the 26 x 1 3/4" has a BSD of 571mm so these tyres are NOT interchangeable.
Tyre Sizing in General
Road Racing Bikes
If you have a road racing bike, chances are that you'll have a 700c x 18 up to 28 tyre (18-28 being the width in mm), 700c referring to the diameter. 700 x 23 is the most common although most road bikes will fit a tyre in this range. Tyres under 23mm wide are not recommended for road riding; especially on rough New Zealand roads. Sometimes road racing bike tyres that are 700c and have a 622mm ISO/BSD measurement are called 27" which is incorrect, 27" will be explained below.
Hybrid or Flat Bar Road Bikes
'Hybrid road bike' is a very broad term and bikes of this kind can have tyres generally ranging from 26mm wide up to 47mm. These could be named something like 700c x 32 or could otherwise be called 28" or 29" - The best idea is to stick to the 700c (French) size designation since it's the most commonly used and understood sizing method, otherwise if you're unsure use the ISO/BSD measurement which would look something like 622 x 32.
Mountain bikes, offroad bikes, comfort bikes and kids' bikes
All of these bikes will use a decimal size, for example 26 x 1.5", 26 x 2.1", 24 x 1.95". Whether the tyre is knobbly or smooth it will use the same sizing system - the first measurement which could be any one of 16", 20", 24" or 26" is a reference to the rough outside diameter of the installed and inflated tyre. The second measurement is the width of the tyre in inches.
12" Tyres
Oddly enough 12" tyres that are still commonly used on kids' bikes, scooters and buggy wheels (such as the Phil and Ted's strollers) still use a fractional sizing system. The tyres are commonly referred to as 12" but they're actually 12 1/2", the most common size being 12 1/2 x 2 1/4". Don't worry though - there is no decimal equivalent to get confused with this fractional size so everyone will know what you mean when you say 12".
27" Tyres
27" Tyres are an older fractional size (pre 1990's) which is commonly found on '10 speed road bikes'. These tyres are obsolete in that they are not used on new bicycles but tyres and tubes are still available. The most common 27" size being 27" x 1 1/4". Although there is no decimal equivalent to 27" tyres, some people incorrectly refer to 700c tyres as 27", these terms and the tyre sizing standards are not interchangeable.
Things to Remember
Tyre Width
you can use any tyre width you like as long as the tyre isnt narrower than 1.5 x the inside width of the rim that it's installed on and the only width restriction is your frame and components; if a tyre is too wide it will rub on the frame, fork, brakes, chain or front derallieur.
Narrower tyres are lighter weight and offer lower rolling resistance and are normally described as being 'faster', wider tyres are generally heavier and slower but more comfortable because of their higher volume which absorbs bumbs and vibration better.
Different Brands and Their Measurements
Different brands may have a preference as to which tyre measurement system they most prominently display on their packaging - Hopefully with the info in this article you won't be confused by this anymore
They also tend to measure tyre width in different ways and the overall width of the tyre once installed and inflated will vary depending on the width of the rim that it's installed on - take the width measurement with a grain of salt and remember that it's there to give an idea of the width rather than being a super accurate measurement.
Tyre Sizing Chart
The chart below contains all tyre sizes - ISO, Fractions, Decimals and French. Use this table to find out the measurements and names in different tyre sizing systems, this will be particularly useful if you have an older tyre size which is obsolete or uncommon.
If you require one of these uncommon tyre sizes we most likely don't stock them or have them listed on the web store but if you need to source tyres or need to find out more about your tyres' measurements don't hesitate to contact us.
ISO Fraction or Decimal French
28-590 26 × 1⅜ × 1⅛
28-622 28 × 1⅝ × 1⅛ 700 × 28C
28 × 1⅝ × 1¼ × 1⅛ 700 C Carrera
28-630 27 × 1¼ fifty
28-635 28 × 1½ 700 B
28-642 28 × 1⅜ × 1⅛ 700 × 28 A
32-239 12 × 1⅜ × 1¼ 300 × 32
32-248 12 × 1¼ 300 × 32 A
32-288 14 × 1⅜ × 1¼ 350 × 32
32-298 14 × 1¼ 350 × 32 A
32-340 16 × 1⅜ × 1¼ 400 A
400 × 32
32-349 16 × 1¼ NL 400 × 32 A
32-357 17 × 1¼
32-369 16 × 1¼
32-390 18 × 1⅜ × 1¼ 450 A
450 × 32
32-400 18 × 1¼ 450 × 32A
32-438 500 × 32 ANL
32-440 20 × 1⅜ × 1¼ 500 A
500 × 32
32-451 20 × 1¼ 500 × 32 A
32-489 550 × 32 ANL
32-490 22 × 1⅜ × 1¼ 550 A
550 × 32
32-501 22 × 1¼ 550 × 32 A
32-508 22 × 1¼ × 1
32-540 24-1⅜ × 1¼
32-541 24 × 1⅜ × 1¼ NL 600 A
600 × 32 A
32-547 24 × 1¼
32-590 26 × 1⅜ 1¼ 650 × 32A
32-597 26 × 1¼
32-622 28 × 1⅝ × 1¼ 700 × 32C
28 × 1¼ × 1¾ 700 × C Course
32-630 27 × 1¼
32-635 28 × 1½ × 1⅛ 700 × 28 B
700 B Course
37-288 350 A Comfort
350 A 1/2 Balloon
37-298 14 × 1⅜
37-337 16 × 1⅜ ANL
37-340 16 × 1⅜ NL 400 A Comfort
400 A 1/2 Balloon
400 × 42 A
400 × 35 A
37-349 16 × 1⅜ NL
37-387 18 × 1⅜
37-390 450 A Comfort
450 A 1/2 Balloon
37-400 18 × 1⅜
37-438 20 × 1⅜NL
37-440 500 A Comfort
500 A 1/2 Balloon
37-451 20 × 1⅜
37-489 22 × 1⅜ NL
37-490 550 A Comfort
550 A 1/2 Balloon
37-498 22 × 1⅜ × 1¼ NL
37-501 22 × 1⅜
37-540 24 × 1⅜
37-541 600 A Comfort
600 A 1/2 Balloon
600 × 35 A
37-565 25 × 1⅜
37-584 26 × 1½ × 1⅜
26 × 1⅜ × 1½
37-590 26 × 1⅜ 650 A
650 × 35 A
37-622 28 × 1⅝ × 1⅜ 700 × 35 C
28 × 1⅜ 1⅝
37-642 28 × 1⅜ 700 × 35 A
40-279 14 × 1½ 350 × 38 B
40-288 14 × 1½ NL 350 × 38
40-330 16 × 1½ 400 × 38 B
40-432 20 × 1½
40-440 20 × 1½ NL 500 × 38
40-534 24 × 1½
40-540 24 × 1⅜ × 1½
24 × 1½ × 1⅜
40-571 26 × 1½ C.S.
26 × 1⅝ × 1½NL
40-584 26 × 1½ 650 × 35 B
650 × 38 B
40-590 26 × 1⅜ × 1½ NL
40-622 28 × 1⅝ × 1½ NL 700 × 38 C
40-635 28 × 1½ × 1⅜ 700 B Standard
28 × 1½ 700 × 35 B
700 × 38 B
44-194 10 × 1⅝
44-288 14 × 1⅜ × 1⅝ 350 A
350 × 42A
44-340 16 × 1⅝
44-428 20 × 1⅝ × 1½
44-484 22 × 1⅝ × 1½
44-531 24 × 1⅝ × 1½
44-584 26 × 1½ × 1⅝ 650 B Semi-comfort
26 × 1⅝ × 1½ 650 B 1/2 Balloon
26 × 1¾ × 1½ 650 × 42B
44-622 28 × 1⅝ 700 × 42 C
44-635 28 × 1⅝ × 1½
28 × 1½ × 1⅝
45-584 26 × 1.75 × 1½ 650 × 45 B
26 × 1½ × 1¾
47-203 12½ × 1.75 × 2¼
47-222 11 × 1¾
47-305 16 × 1.75 × 2
47-317 16 × 1¾
47-355 18 × 1.75 × 2
47-406 20 × 1.75 × 2
20 × 1.75
47-419 20 × 1¾
47-501 T 24 × 1¾ R 600 × 45 C
47-507 24 × 1.75 × 2
24 × 1.75
47-520 24 × 1¾
47-559 26 × 1.75 × 2
26 × 1.75
47-571 26 × 1¾ 650 × 45 C
26 × 1⅝ 650 C S.C.
47-622 28 × 1¾ 700 × 45 C
28 × 1.75
28 × 15/8 1¾
54-298 14 × 2 × 1¾
54-305 16 × 2
54-400 20 × 2 × 1¾
20 × 2 F 4 J
54-406 20 × 2.00
54-428 20 × 2
54-559 26 × 2.00
54-571 26 × 1¾ × 2
26 × 2 × 1¾
26 × 2 650 × 50 C
54-584 26 × 2 × 2½
26 × 1½ × 2
54-609 28 × 2
57-239 300 × 55 A
57-251 T 315 × 55
57-305 16 × 2.125
16 × 2.125 × 2
57-390 450 × 55 A
57-406 20 × 2.125
20 × 2.125 × 2
57-507 24 × 2.125
24 × 2.125 × 2
57-559 26 × 2.125
26 × 2.125 × 2
62-203 12½ × 2¼ 320 × 57
62-305 16 × 2.125
67-203 13 × 2½ 330 × 65
67-381 20 × 2½