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I went to a bike shop for new tires. I did not know which tires fit on my bike, so I just showed them my bike.

When I took a look at the new tires, there was a label at the side, which says:

40-622 (700x38C-28x1 5/8 x 1 1/2)

What do all these numbers mean? I am asking for two reasons:

  • I would like to find the right tires for my bike in the future myself
  • When buying another bike, I would like to buy one where I can use this tires as well
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Note that a "700" tire is a standard European "road" tire. If you go into a bike store and ask for a "seven hundred, thirtyeight" the sales clerk (if not a total dunce) will know exactly what you mean. If you ask for a "forty, six twentytwo" they might have to check the labels. –  Daniel R Hicks Apr 9 '13 at 11:35
    
Also note that if your bike came with tires of that width, you can generally go about 3mm wider or narrower (vs the "40" or "38" number) without problems (though if you go too much wider the tires may rub). –  Daniel R Hicks Apr 9 '13 at 11:39
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1 Answer 1

up vote 8 down vote accepted

The 40 is the inflated width in mm and the 622 is the internal diameter in mm. It's the international standard ISO-5775 for tire sizes. In brackets are the French size (700mm outer diameter x 38mm width) and the Inch size (28 outer diameter x 1 5/8 height x 1 1/2 width)

Wikipedia has a very detailed explanation of tire sizes and designations, I confirmed my answer on this page.

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So, if I look for 40-622 tire size, they will fit on my bike? Also, if I buy a bike that has 40-622 tires on it, I will be able to use my current tires on it? Do I have to take care on the other numbers, then? That are the reasons why I am asking. –  Uooo Apr 9 '13 at 9:16
    
All 40-622 tires are a standard size, if that is what your bike has on it now they'll fit. Yes, a bike with 40-622 tires will take other 40-622 tires. No, they're essentially saying the same thing for countries who don't apply to the whole ISO standard thing. Essentially one is metric, one is empirical and the other is French. –  DWGKNZ Apr 9 '13 at 9:25
    
empirical -> imperial :) –  Mladen Jablanović Apr 9 '13 at 11:18
    
One needs to beware that there are two different, incompatible inch sizing schemes. A width expressed in fractions (1 1/2") is not the same width OR DIAMETER as one expressed in decimal (1.5"). Sheldon Brown had some info on this. –  Daniel R Hicks Apr 9 '13 at 11:30
    
As Sheldon explains, the "outer diameter" isn't the outer diameter of the actual tyre, it's the outer diameter of the nominal size tyre first (or typically) used on that rim at the time that size system was established. A 40-622 really is about 700mm, but a 20-622 racing tyre isn't. A fat 26" mountain bike tyre can have an actual diameter larger than a 27" or 28" tyre. (And 29" mountain bike tyres use the same rim diameter as one of the sizes known as 28".) –  armb Apr 11 '13 at 16:43

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