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Bicycle tyre sizing and dimension standards

What do size marks on bicycle tyre package mean, how to “read” them, which bicycle tyre size can fit a given rim? This post answers all those questions, providing an easy, uniform, standardized way to tell a tyre (tube and rim) size using ISO (ETRTO) standards. For detailed tube sizing gude, see: Bicycle tubes – types, valves and sizing explained. Effect of tyre size on speed and comfort is explained here: Are narrower tyres “faster” – rolling resistance.

If you have any questions (or additions and corrections), please use the BikeGremlin forum:
www.bikegremlin.net

Table Of Contents (T.O.C.):

TL/DR

  1. Expressing (noting) bicycle tyre dimensions
    Table 1: standard bicycle tyre sizes
  2. Tyre widths
    Table 2: which tyre width fits which rim width
    Table 3: which fat-bike tyre width fits which rim
    Table 3b: Schwalbe’s complete size chart
    2.1. Why is it important to use an optimal tyre with for your rim width?
  3. Frame fit room (maximum width)
    Table 4: real tyre height relative to its pressure and nominal size
    Table 5: real tyre width relative to its pressure and nominal size
  4. Tyre size and fitting video
  5. Sources


TL/DR

Here, I’ve explained how you can read and understand bicycle tyre size marks (why and how 700 C is the same diameter as 28″ x 1.75 or 29″ – all being the same 622 mm diameter tyres).

I’ve also explained which tyre widths you can fit on your rim and bicycle frame (and how to measure your rim width and frame tight spots).

In the bicycle tubes article I’ve explained which tube dimensions can fit which tyre sizes (and valve types).

– T.O.C. –


1. Expressing (noting) bicycle tyre dimensions

At first, tyre dimensions were expressed through mounted (and inflated) tyre outer diameter. That is why today we still often note tyre sizes like 26″ (now less often), 27.5″ or 29″ for MTB, and 28″ for road bicycles. A 26″ tyre fits on a rim with a 559 mm diameter. When a 2″ wide tyre is mounted on such rim, the outer diameter of such wheel with an inflated tyre is around 660 mm (26″). To further complicate things, different standards were made in different countries. This led to situations that same sized tyres were differently noted, or that the same dimension note was used for tyres that differ in size. Does this sound complicated and confusing already? 🙂 Here’s a picture that takes 26″ “size” as an example:


That is why ISO standard notation was introduced and is in use today. Standard was introduced by ETRTO (The European Tyre and Rim Technical Organisation). Diameter of wheel tyre bead seat in millimetres preceded by tyre width in millimetres. Tyre width is also a bit non-exact measurement. It is width of an inflated tyre mounted on a rim of standard width for that tyre size. However, the most important information: wheel bead diameter is noted exactly in millimetres, so there can be no confusion. 559 wheel and tyre are always compatible (at least in terms of diameter, see about tyre and rim width compatibility below).

When bead seat diameter (BSD) is known, a tyre of appropriate dimensions in mm is required. It is as simple as that.


For example, the 26″ wheel diameter is 559 mm and it can take practically any tyre of that BSD, whether wider, or narrower, such as 47-559 (26×1.75″ by old nomination), 60-559 (2.35×26″ by old nomination) and so on. All the manufacturers today mark tyres with ISO dimension standards, sometimes adding old nominations as well, but ISO is always noted and can be used as a safe(st) reference.

Standard road bicycle wheel size today is 622 mm and it usually takes tyres of 23-622, or wider 25-622. Today when off road bicycles with wheels larger than standard MTB wheels started to be popular, it’s wheels are marketed as 29″, but in fact are 622 wheels with wider tyres (so that outer diameter is close to 29″). Tyres for those bicycles are always marked with ISO standard (sometimes along with the “old” standard 29″) saying something like: 57-622, 60-622 and similar, depending on tyre width.


In case a tyre has no ISO (ETRTO) marks, here is a cross-reference:

ISO (ETRTO)
Bead Seat
Diameter
Traditional Designations
787 mm36 inch
686 mm32 inch
635 mm28 x 1 1/2, 700 B
630 mm27 x anything except “27 five”
622 mm700 C, 28 x (two fractions), 29 inch, 28 x 1 1/2 F.13 Canada   Road 28″ wheels and MTB 29″.
599 mm26 x 1.25, x 1.375
597 mm26 x 1 1/4, 26 x 1 3/8 (S-6)
590 mm26 x 1 3/8 (E.A.3), 650 A
587 mm700 D
584 mm650B, 26 x 1 1/2, 27.5″  MTB 27,5″ wheels
571 mm26 x 1, 26 x 1 3/4, 650 C
559 mm26 x 1.00- x 2.125, also fatbike tyres up to 5 inches wide MTB 26″ wheels.
547 mm24 x 1 1/4, 24 x 1 3/8 (S-5)
540 mm24 x 1 1/8, 24 x 1 3/8 (E.5), 600 A
520 mm24 x 1, 24 x 1 1/8
507 mm24 x 1.5- x 2.125 – Big kids bikes with 24″ wheels.
490 mm550 A
457 mm22 x 1.75; x 2.125
451 mm20 x 1 1/8; x 1 1/4; x 1 3/8
440 mm500 A
419 mm20 x 1 3/4
406 mm20 x 1.5- x 2.125  – Kids small 20″ wheels, BMX.
390 mm450 A
369 mm17 x 1 1/4
355 mm18 x 1.5- x 2.125. Kids’ bikes with 18″ wheels.
349 mm16 x 1 3/8
340 mm400 A
337 mm16 x 1 3/8
317 mm16 x 1 3/4
305 mm16 x 1.75- x 2.125  – Kids’ 16″ wheels.
288 mm14 x 1 3/8″
254 mm14 x 2.00. Kids’ 14″ bike wheels.
203 mm12 1/2 X anything. Small kids’ 12″ wheels.
152 mm10 x 2
137 mm8 x 1 1/4
Standard bicycle tyre dimensions (ISO, and obsolete standard notation cross-reference)
Table 1

– T.O.C. –


2. Tyre widths

After explaining tyre dimensions, a few words on tyre widths. Generally, narrower tyres are good for fast road riding on pavement, while wider tyres are better suited to rough terrain, or heavily loaded bicycles (heavy rider, carrying children or heavy baggage on a bicycle etc.). Depending on rim width, a range of tyre widths can be used. The important measure here is inner rim width. Outer rim width is irrelevant (for this purpose), just the inner rim diameter.


The following table tells the range of acceptable tyre widths depending on inner rim width, expressed in mm, according to ISO (ETRTO) standard:

Tyre width
(mm) /
Rim width
18
20
23
25 28 32 35
37
40 44 47 50 54
57
60 62
13xxxx
            
15  
x
xx
x
          
17   xxxxxx
x
x
x    
19    xxxxxxxxxx  
21      xxxxxxxxxx
23       xxxxxxxxx
25         xxxxxx
x
27          x
xx xx
x
29            xxxx
Which tyre width can fit which rim widths (in millimetres)
Table 2


Fat-bicycle tyre sizing chart:

Tyre width
(mm) /
Rim width
65
2.60″
70
2.80″
80
3.10″
100
4.0″
110
4.40″
115
4.50″
120
4.80″
30
xxx
   
31xxx
 
32
xx
33
xxx 
34
xxx   
35
 xx    
40
  x   
45
   x  
50
   x
70xxx
100xx
Which fat-bike tyre width can fit which fat-bike rim widths (in millimetres)
Table 3


Below is a chart which includes many modern (more recent) tyre and rim widths. It was made by the Schwalbe company and in my experience it is a safe guide (I’ve even exceeded the there-recommended ranges without problems). Both the dark-blue Schwalbe range, and the light-blue ETRTO range are fine – as long as you stay within either of those, you’ll be fine:

– T.O.C. –


2.1. Why is it important to use an optimal tyre with for your rim width?

If a tyre that is too narrow is mounted on a wide rim, the rim can easily be damaged on a bump. If too wide a tyre is mounted, there is a risk of the tyre coming off a rim (with a loud explosion of the tube). Either of the two extremes can reduce traction and comfort (shock absorption), and distort the optimal tread/knob design. In addition to that, using a tyre that is too wide for the rim width can expose the tyre’s sidewalls to cuts (I’ve had this “pleasure” with a rather expensive 28mm tyre mounted on a 13 mm wide rim).


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– T.O.C. –


3. Frame fit room (maximum width)

If there’s limited space for fitting tyres in a frame, note that rim width also influences tyre width and height when mounted:

Difference of outer dimensions when mounted on various width rims.
Difference of outer dimensions when mounted on various width rims.


It should be also noted that one nominal tyre size (e.g. 622-28), in various models and manufacturers, is not of the same actual width when mounted and inflated. Some models are known to be of a smaller “real” size, some are known to be larger. If, for example, the old tyre has a nominal width of 23 mm, and one considers replacing it with a wider one of 25 mm (nominal) width, and there is only about two mm extra room, it should be confirmed what the actual tyre widths when mounted are. If the old 23 mm tyre is among the “narrower 23s”, and the considered 25 mm one is among the “wider 25s”, it is very likely that the wheel will not fit into the frame with the new tyre.

Pictures below are taken on a frame with lots of extra room for wider tyres (and mudguards). They are just a demonstration of where the “tight” spots usually are, and where attention should be paid (and measuring taken) before going for wider tyres. Depending on frame geometry and brake type, some other spots may be the tight ones. It should always be checked and measured at the tightest spot, with the least tyre clearance – and that is usually in (one of) these places:


Table overview of how tyre inflation pressure affects its real height, depending on its nominal size (dimension) – inner rim width used or measuring was 19 mm:

Tyre model and
nominal dimension
Real
height
at
3 bars
pressure
Real
height
at
4.5 bars
pressure
Real
height
at
6 bars
pressure
Continental
Grand Prix 4-Season
ETRTO 622-28
27 mm27.5 mm28 mm
Continental
Terra Trail
ETRTO 622-35
32 mm32.5 mm32.75 mm
Schwalbe
Lugano 2
ETRTO 622-25
22 mm22.5 mm22.75 mm
Real tyre height relative to its inflation pressure and nominal size
Table 4


Table overview of how tyre inflation pressure affects its real width, depending on its nominal size (dimension) – inner rim width used or measuring was 19 mm:

Tyre model and
nominal dimension
Real
width
at
3 bars
pressure
Real
width
at
4.5 bars
pressure
Real
width
at
6 bars
pressure
Continental
Grand Prix 4-Season
ETRTO 622-28
29.5 mm29.7 mm30.1 mm
Continental
Terra Trail
ETRTO 622-35
34.7 mm34.8 mm35.15 mm
Schwalbe
Lugano 2
ETRTO 622-25
24.6 mm24.8 mm25.3 mm
Real tyre width relative to its inflation pressure and nominal size
Table 4


– T.O.C. –


4. Tyre size and fitting video

Can I put a wider/narrower tyre on my bicycle/rim?

– T.O.C. –


5. Sources


Related post – To what pressure should I inflate my bicycle tyres:

To what pressure should I inflate my bicycle tyres?
To what pressure should I inflate my bicycle tyres?

If you have any questions (or additions and corrections), please use the BikeGremlin forum:
www.bikegremlin.net

The existing comments posted under this article (questions and answers) have been moved to this BikeGremlin forum thread:
https://www.bikegremlin.net/threads/bicycle-tyre-sizing-and-dimension-standards-article-comments.103/

– T.O.C. –


Last updated:


Originally published:



63 thoughts on “Bicycle tyre sizing and dimension standards”

  1. [Hi Relja,
    Thanks for all the good advise and suggestions It still left me with a question:
    I have a Shimano Ultra WH6800 Wheelset. I would like to put tape on the wheelset, however I don’t know the correct width of the tape to useThe tubeless tire size is 700 x 25 from Schwalbe.
    I appreciate your expertise and knowledge
    Marcel

    • Hi Marcel,

      Short answer:
      – Measure the rim’s internal width (first picture in 2nd chapter of this article – showin 19 mm in that case)
      – Add 3 to 5 mm to what you’ve measured.
      – You’ve got the optimal tubeless rim-tape width! 🙂

      Long answer:
      When the rim-tape is installed, its edges should climb a little bit up the “vertical” sides of the rim – but not too much.
      The idea is to achieve two goals:
      1) Prevent the rim-tape that is too wide, and climbs too high up the rim’s sidewalls, from interfering with the tyre seating onto the rim.
      2) At the same time, by having the rim-tape slide up the sidewalls by 1 mm, or a bit more, keeps its edges covered by the tyre.
      This prevents any air pressure from sliding under the rim tape, and “trying” to leak.
      Also, when mounting, or removing a tyre, rim tape sides won’t get pushed by the tyre, or even by the tyre lever (accidentally), since the rim tape and the tyre will slightly overlap.

      Basically: tubeless rim tape should fit a bit wider than I prefer with “standard” (tube tyre) rim tape, but still not too wide so it reaches the top of the rim.

      I will add a drawing to the rim-tape article, explaining the optimal rim-tape widths for both tube, and tubeless tyres.

  2. Hello and thank you for the article.

    I would like some help. I have shimano rs 11 622*15c with gp400s2 25mm.
    I would like to fit the new gp 5000 28mm. Do you think they will fit properly and will have a benefit from the 28mm or should i stick with the 25mm?
    As you will probably know the gp4000s2 25mm are wider than the 25mm gp 5000.

    Thank you in advance.

    Billys

    • Hi Billys,

      Measure the rim-s inner width and check table 2 to see if it will nicely fit the rim.
      In my experience, 13.5 mm wide rims (and wider – up to, including, 19 mm) will work nicely with 28 mm wide tyres.

      Before doing that, measure the tight spots on your frame with the current tyre (25 mm wide one).
      Pictures in the chapter 3 of this article show these tight spots. The bike in the pictures has huge gaps, loads of clearance, but is good for the demonstration. If your bike has 3 mm, or more room, I’d expect the 28 mm tyres to fit.
      If it has less, then even if the tyres do fit, the clearance will be too small in case something gets tuck on the tyre, or a wheel deflects even for a little (depending on where the tight spots are). I wouldn’t risk in that case.

      An expensive solution for more comfort, if the 28 mm tyres won’t fit, is getting wider rims – with 17 mm inner with, and mounting 25 mm wide tyres – that will provide greater air volume, compared to 13, or 14 mm wide rims, without the tyre being much “taller” to catch onto the frame.

      Relja

  3. Thank you very much for your faat response.

    Regarding the tight spots, my only concern is at the rear rim brake as you can see at the attached link. But as the gp 5000 28mm is slightly bigger than the old gp 4000s2 25mm, i don’t think i will have problem.

    So in your opinion the 28mm tyres will fit ok at my roms and not be like “balloons” wich will lead in bad behaviour?

    A new pair of wheels might come in summer, which will be wider so 28mm would be also a good investment. But for the time, a new pair of tyres is a must.

    Thank you.

    Billys

  4. Great article man! I bought an old bike and trying to restore it. On my wheel it is engraved 28* 1 5/8, what does that mean in mm? 28 is for diameter, but what’s 1 5/8?

    • Hi Marc,

      According to table 1 in this article, that’s probably a 622 mm tyre. The old, “exotic” dimension notation is not really exact. I’ve tried to explain it at the start of this chapter as best as I could.

      In this particular case 1 5/8 probably refers to the tyre’s width, being about 1 and 5/8 of an inch. Which is roughly 40 mm, but I believe this tyre is closer to the ETRTO equivalent of 622-37.

      Relja

  5. Love your site, use it at the bike shop where I work sometimes. However you should update this article because it states the 26″ or 559 is THE mountain bike size when no major brand has made a 26″ MTB in the better part of a decade that’s not meant for children. It’s all 27.5″ and 29″ now and has been for some time.

    • Hi Sage,

      Hahaha – laughing at myself now. 🙂
      Yes, you are absolutely correct. Thank you. I’ll edit the article.

      “Tell me I’m old, without saying that I’m old.”

      – You say MTB when you mean 26″ wheels.

      🙂

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