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I thought that all 700c/622 wheels were "29er" compatible or basically the same size; 622mm.

I had the tire off a Mavic Aksium wheel yesterday and was surprised that it is labeled 700c 28''.

Is this a 29er compatible wheel? Is 28'' meant to be the approximate outside diameter on a road tire, and 29'' the approximate diameter of a mountain tire, or am I misunderstanding?

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    It's called a 28" wheel because it's smaller than a 27" wheel. Make sense? If so you've been immersed too deeply in the illogic of wheel sizing. – Daniel R Hicks Apr 4 '17 at 0:22
  • "Is 28'' meant to be the approximate outside diameter on a road tire, and 29'' the approximate diameter of a mountain tire". Yes, you are correct in this regard, several tire sizings are based on assembled rim+tire outside diameter. MTB tires marked 26x2.1 have an approximate outer diameter of 26 inches. – Jahaziel Jan 31 at 15:33
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As usual, Sheldon's got the answers.

ISO 622 is the unambiguous way of referring to the following rim sizes:

  • 700c (you see this marketing on road, hybrids; this is from the French system; the c is often dropped, but there are rare a,b sizes)
  • 29"x decimal (you see this on mountain bikes; usually only applied to wide rims)
  • 28"x decimal (particularly in Germany)
  • 28" x some fractions (seems to be a rare Canadian / northern European thing).

700 mm is roughly 27.5 inches, so if you mounted a reasonable tire on it, you'd get around 28 inches (hence the name 28"). For mountain bikes, you'd get a bigger tire giving an outside diameter of 29"+.

In theory, any tire which can be mounted to a rim marked as any above sizes can be mounted to the others, but in practice you want the rim width to be appropriate to the tire size you're mounting.

In terms of which way you should refer to this wheel size, ISO 622 is unambiguous. If its being used on a road bike or hybrid, 700c is also a good way to refer to it. If its being used on a mountain bike with a big tire, 29" is also a good way to refer to it.

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  • Note that 28" tires do not all fit 622 rims. It depends on the specific width, a la 26" fractional wheels. – Daniel R Hicks Apr 4 '17 at 0:26
  • I can confirm 29er rims can be used with 700c tires, I have done it twice. I once assembled a dutch bike using a frame designed for 28" wheels using rims labelled for 29" mountain bikes, and 700c x 35 tires. The size is close enough to a 28" assembled rim+tire. However, a 28" tire has a bead 4 milimetres or such too big to fit a 622 rim. I currently ride a bike with 29er rims and 700c x (dont remeber) tires on a 26er mountain frame (it has a lot of clearance). – Jahaziel Jan 31 at 15:27

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