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Bicycle tyre sizing and dimension standards

Updated: 15/10/2020.

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.

Contents:

  1. Expressing (noting) bicycle tyre dimensions
    Table 1: standard bicycle tyre sizes
  2. Tyre widths
    Table 2: which tyre width fits which rim width
  3. Frame fit room (maximum width)


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 see MTB tyres noted as 26″ tyres, or 28″ tyres for road bicycles. Rim diameter of a MTB is 559 mm. When a 2″ wide tyre is mounted on such rim, the outer diameter of such wheel with inflated tyre is around 660 mm (26″). To further complicate things, differrent standards were made in different countries. That led to situations that same sized tyres were differently noted, or that a same dimension note was given for tyres that differed in size. Does this sound complicated and confusing already? 🙂 Here’s a picture that takes 26″ “size” as an example:

Bigger wheel with a narrower tyre has the same outer diameter as a smaller wheel with a wider tyre.
Bigger wheel with a narrower tyre has the same outer diameter as a smaller wheel with a wider tyre.


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.

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

Bead seat diameter and inner rim width - all that matters.
Bead seat diameter and inner rim width – all that matters.


For example, MTB 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 producers today mark tyres with ISO dimension standards, sometimes adding old nomination as well, but ISO is always noted and can be used as a safe(st) refference.

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.

Tyre with dimensions noted in ISO, English and French standard.
Tyre with dimensions noted in ISO, English and French standard.


In case a tyre has no ISO marks, here is a cross reference:

ISO Bead Seat DiameterTraditional 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
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.
254 mm14 x 2.00
203 mm12 1/2 X anything. Small kids 12″ wheels.
152 mm10 x 2
137 mm8 x 1 1/4
Table 1: standard bicycle tyre dimensions (ISO, and obsolete standard notation cross-reference)


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 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.

Rim cross section, with inner and outer diameter. This one has 19 mm inner rim diameter.
Rim cross section, with inner and outer diameter. This one has 19 mm inner rim diameter.


The following table tells the range of acceptable tyre widths depending on inner rim width:

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


If a tyre that is too narrow is mounted on a wide rim, rim can easily be damaged on a bump. If too wide a tyre is mounted, there is a risk of tyre coming off a rim (with a loud explosion of the tube).


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, 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:


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?
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19 thoughts on “Bicycle tyre sizing and dimension standards”

  1. I have a road bike and hybrid bike with front tire sizes 700×23 and 700×40. I want to get one wheel that can fit on both bikes (the wheel has an electric motor). I believe the road bike rim inner width is 15mm. Is it possible to fit a wheel with 17mm inner width on the road bike? Can the road brakes be adjusted to fit wider rim? Can i get brakes that will fit wider rim?

    Reply
    • Short answer: yes, no problems.

      Brakes on a rim with a 2 mm more outer width need to go out by just 1 mm at each side.

      There is a tendency for road bike rims (and tyres) to go wider. For both comfort and aerodynamics (wider tyres being more aero on wider rims, than narrower tyres).

  2. Your image showing the cross-section of 2 tires mounted on 3 different rims at different pressures looks like it may contain many errors.
    The same tire is shown as being wider and taller on a wider rim, than it is on a narrower one. Assuming all have 622 bead seat, how is this possible? What’s more, it appears taller and wider at 75psi than it does at 100psi on the same rim.

    Reply
    • It is counter intuitive, but yes, a tyre can get both wider and taller on a wider rim. Depending on rim’s inner width (bead seat width) and tyre’s width.
      As for the rest – which cases in particular you think are problematic?

    • Most of them are problematic actually.
      A 25mm [email protected] is same height but wider than the same tire @100psi on the same Ardennes rim.
      A 23mm [email protected] is same height but wider than the same tire @100psi on the same Ardennes rim.
      (the only 2 I’m not questioning is on the narrowest rim).
      —————————————————————————–

      PS: can you follow the link to my website that I entered ( Velo76.com ) – it will redirect you to my FB group, you can see me there as admin (Timm S…) and add me. I’d like to bring something else up with you – it might be more productive to do it in messenger than a reply every few months on here.

    • Will do – though I reply almost daily on most comments here. Definitely not “every few months”.

      As for the graph – [email protected] is mounted on a 20.7 mm inner rim width, while the 100 PSI graphs are made for 17.8 and 13.6 mm rim widths.
      Wider rim makes tyre’s circumference effectively larger. That is the point. So it can be wider, while not being of lower height, even under a bit lower pressure.

  3. I’d also like to raise the question of the TIRE VERSUS RIM WIDTHS in the table.

    These types of tables can be very helpful, but I would like to give a word of caution about it. I’d like to illustrate my point with a personal experience, if you’ll just bear with me:
    I went to slightly wider tires, up from my usual 23c-25c, to 28c, but didn’t change my wheels.
    700x28C tires, mounted on 15mm inner width rims, at 80psi (this is the max for many affordable 28c tires, although a Continental can go much higher. The ones I had on that day were the Michelin Dynamic).
    Cornering on asphalt, I could feel the back wobble as the tire tried was folding under the rim and redressing itself, ove and over, as it went over a very slightly uneven paved surface (just your usual city road). It would bend, then redress itself with rotation when the road dipped down slightly, then folded again. This felt very dangerous. Luckily it didn’t fold under completely, but had I gone a little bit faster, it surely could have.
    So in this example, for a 15mm rim, 32c should be stricken off that line, and perhaps the 28C as well (80psi is the max on many 28c tires from Kenda to Michelin, so you can’t just say to up the pressure).

    True, tire width and pressure depends on riding style and type of riding. A mountainbike, on dirt trails, can take much wider tires per rim width, than a road bike can. The MtB will slide on dirt surface, the road bike’s tires will grip and not slide, when cornering hard (unless you have very hard budget tires on the road bike).

    I think you need to err on the side of safety here. And take off a at least 1 checkmark from the right on some of those “acceptable” tire sizes per rim widths. It won’t help a young enthusiast who likes to ride fast, and has an accident, slipping under a truck in a turn, because the tire flopped over, sending him into a high-speed slide (or off a cliff). It won’t help the more tame cyclist who is in an emergency situation and makes a sharp turn.

    A 32c on a 15mm rim is definitely a no-no. 28C on the 15mm rim is debatable (sometimes safe, sometimes not as in my anecdote). In fact, the entire table could be shifted to the left, in order to be more accurate. I realize that some manufacturers will publish overly optimistic numbers, but that’s just because they want to sell more tires – and if they tell people to buy new wheels to get wider tires, they won’t be selling wider tires to folks who already have tires.

    Reply
    • I ran 28 mm Continental Grand Prix 4 seasons on 13.5 mm wide rims with no problems. At 5 to 6 bar pressure.
      For all I know, the table is more on the conservative/safer side – at least in my experience.

      It is also my experience that manufacturers are more often “too conservative”, than “too optimistic” – probably in order to avoid any law problems.

      Your feedback is valuable to me – it certainly requires more looking into. However, it does not align with my own previous experience, nor with the experience of other riders I know. For the given table, I took info from Mavic (as a rim manufacturer) and Schwalbe (as a renowned tyre manufacturer) – using the more conservative option in cases of any mismatch – and making sure it does align with my own experience.

    • I actually run Bontrager 28mm AW1 Front and 32mm H1 Rear on my 23mm rims very successfully for over 18 months now mostly road but some gravel paths too.
      These are both off your chart on the left hand end of the scales.
      These tyres were both ‘last in stock’ at my LBS at the time (hence different sizes) and sales assistant assured me it was ok and a good move from my 36mm Clement X’plore MSO chunkies provided with my gravel bike which made so much noise on the roads.

  4. Hi,
    Thanks for such a nice explanation. First a little background. I have a Drag bike Rodero TE exact specification like this one here; https://dragzone.bg/en/drag-rodero-te-bike-2018. It originally can with the Schwalbe Spicer K-Guard, 30-622 tires though the rim is designated at these numbers: ETRTO 622x13c. There is also this numbering, ERD: 593, I am not sure what ERD means. Anyways, while the ‘conservative’ chart says rim sizes of 622 x 13c (700x 13c) can fit as far as 25mm (700x 25c), my bike came fitted with 700x 30c. I have had no problems whatsoever until I recently changed to Maxxis Relix (SilkShield, One70) 700x23c tires because it seemed fine that they will fit nicely and 25c ones were not available. The roads that I am riding these days are a combination of gravel and tarmac. I have had flat tires several times and seems to me that this purchase hasn’t paid off. I want to change my tires to gravel types ones but I am eternally confused with the sizes. Looks like my rim can take as much as 700x30c, should I look for these sizes for gravel type tires? Or should I buy a separate wheel-set dedicated to gravel? While having a new wheel-set sounds nice, I am not very sure if my rim brakes (mechanical) and the 10 speed Shimano Tiagra cassette will be compatible. What will be the best course of action? Thanks in advance.

    Reply
    • ERD is “effective rim diameter” – relevant for wheel building, when calculating the optimal spoke lengths. In this video, at 6:40 I explain how it is measured:
      https://www.youtube.com/watch?v=i5ywzfr_dCg&list=PLlbCLBTvuIssCHYrqh9BM8IrtEV2SaD_3&index=4

      As for the tyre sizes, the chart is rather conservative, at least in my experience. Also, some tyres are made “half a size” smaller, or larger, than what is noted on the sidewall. So you might “get away” with tyres wider than 25 mm on 13 mm rims. I would definitely measure the rim’s inner width just to be sure.

      Having said this, wider rims will provide for more air volume inside the tyres, since tubes will expand more inside the rim, hence probably allowing for somewhat more comfortable ride with the same size of tyres, compared to narrower rims. The differences are not night and day, but they do exist.

      I personally don’t like tyres narrower than 28 mm, even on road bicycles. Wider ones don’t need very high pressure, so they don’t have to be topped up too often and can be inflated with a small, cheap, portable pump that fits a patch kit easily. Also, lower pressure (wider) tyres are a lot less prone to punctures by sharp rocks, or glass shards, at least in my experience.

  5. Hi. Thanks for your information in this article. I’m having trouble relating what I find in articles such as this to the tyre sizing for my daughter’s bike. She has a smaller bike being a child, 20 inch wheels. When I was shopping around for new tyres the narrowest I could find at 20 inch was 2.15 inch width. But the tyre I bought looks considerably wider than the existing one. I’m not sure it will fit. So i used your width table. Her inside rim width is 15 mm, and the table seems to suggest a max tyre width of 1.26”. But the tyre she has now is 1.5” and that looks fine. So I’m thinking that I have misunderstood what the tyre width in the table actually is.

    Would you be able to help me check my understanding of the table? Thanks for any help you can give.

    Reply
    • The given table is rather “conservative” – in terms that it gives combinations that will most certainly fit and work fine, with practically any rim and tyre make/model/diameter.

      I have run combinations that are out of the limits given by the chart, with no problems.

      So, to be on the safe side (without being able to see how the tyre fits a rim), the table should be respected.
      Especially since some tyres are made to be a bit wider, or narrower than their sizing specifications show (depends on the manufacturer, and tyre model/mold).
      Having said all that, bearing in mind that 1.5″ tyre is working fine, I wouldn’t shy away from using that width of tyres – just making sure they are seated well.

  6. Hi there,
    I have an old Gazelle city bike of 1973 with the tire dimensions of 28 x 1 3/8 x 1 5/8. It is quite difficult to find tires of those dimensions in my country, Indonesia. What is the alternative tire dimensions that suitable/compatible to the current tires dimensions? Any suggestion? thanks

    Reply
    • Most tyres have ISO marks as well, especially ones made in the past 20 years.
      If these don’t, however, I would try with 37-622 (32 mm wide “28 inch”) tyres.

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