Fuji 4130 bike with ARAYA Japan rim 26x1.50 HE VP-20 Old tires are dryrotted. ( old tire code reads 26x1.80 c-863) have no idea what to buy to fit. (rim measures 22" diameter, roughly)

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26 means 26 inch and is the nominal diameter of rim and tire. It basically means the smaller type of wheel used on older MTBs, with a rim diameter of 559mm. ('27.5' - 584mm and '29' - 622mm being the other sizes in more common usage now.) 1.80 is the nominal tire width in inches also.

Some MTB tire manufacturers still use the inch measurements, some use the ETRTO size system which uses millimeters.

You definitely need a 26'/559mm MTB tire, but you have choice in tire width as a range of widths will fit on a given rim width. The safe choice is to stay with 1.8", but you could go a little wider if you frame and rim brakes have enough clearance.

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    The measured diametre of 22" is also close enough to 559 mm (unless roughly means +/- 1). Here it is quite certainly right. However, at some places 584 mm tyres are also labelled as 26 inch (A historical standard had tyres with 650 mm outer diametre mounted on such rims, that's a little under 26 in). This is not in every context so clear cut, and one always ought to measure the rim's diametre at the bead bed like @o-biker did.
    – gschenk
    Commented May 5, 2019 at 0:32
  • Thanks for the #559 idea. I ordered a 26" tire but it is way too big. Then I read that the Fuji 26 does not match our 26", so I measured the wheel frame and it is shy of 22 inches in diameter, so I couldn't identify a tire to select to fit this diameter. (In my case roughly is 1/4-1/2 inch)
    – o-biker
    Commented May 5, 2019 at 0:33
  • The rule of thumb is that inch sized tires with decimal and fractional inch widths do not fit the same rim even if the nominal diameter and width are the same. Did you order a 26 x 1 3/8 tire?
    – ojs
    Commented May 5, 2019 at 10:04

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