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I'm on an extended bike tour on an... unusual... bicycle, and I've run out of spares. DECATHLON in the Czech Republic doesn't seem to sell tubes in my size (I've tried 3 already), and I don't have time to go crawling through every bike shop in the city hunting for them or to have them ordered in.

Is there anyway in Prague where I can buy any size of tubes that fit these tyres off the shelf? Valve type doesn't matter.

What tubes are a suitable substitute?

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    Or ask there if there is a common type that will work for you. – Willeke Oct 11 '20 at 20:05
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    Forget 27x2.125. Look for the ETRTO number and use that instead. – Michael Hampton Oct 12 '20 at 12:29
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    @kixorz they have one or two online that would certainly work; it may not have the right numbers on the box, but someone knowledgeable should be able to pick one out. That of course is more likely in a proper bike shop than decathlon – Chris H Oct 14 '20 at 14:06
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    Did you run out of tube patches too? – Swifty Oct 15 '20 at 16:28
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    @Swifty perhaps given that the OP seems willing to use the a Presta valve in a Schrader hole, they've all failed near the valve stem – Chris H Oct 15 '20 at 16:38
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Tl;dr: use 700c or 29"

27x2.125" is very rare. 27x2⅛" would be more likely, and wouldn't quite be the same thing, but for tubes the answer would be the same. Generally though, 27" tyres are narrower than this, up to about 40mm or 1 1/2"

Schwalbe says that for 27" tubes you should use 700c, which are very common. The bead seat diameter of 700c is 622mm; for most 27" sizes it's 630mm. As your tyres are on the wide side, you'd want to use 29x2.1" (as 29" is a marketing name for wide 700c)

Tubes are really rather forgiving. Examples: I'm currently running a 26" tube in one wheel of my 29er hardtail (a pain to fit, but I'd taken the wrong tube with me and had to get home); I've replaced a tube with a puncture only to find that I'd been riding one old bike for a year on a 26" tyre with a 24" tube.

Note that the width is also given as a range, so one tube might be suitable for 1.5-2.4" widths. Schwalbe's SV19 is a common example tube, and is specified as suitable for ETRTO diameters from 584mm (27.5") to 635mm (28x1 1/2"/700B) and widths from 40-62mm. I wouldn't choose it for the very largest diameter and width specified, but it would work.

For info, tyre sizing systems are bizarre - 1/4 is not the same as 0.25 for sizes in inches, and 29"=28", while 27">27.5" (and can be bigger than 29").

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  • Isn't 27" also a designation for ETRTO 585 (On GCN they call it "650b"). It's the size between a regular 28" (ETRTO 622) and 26" (ETRTO 556). – gschenk Oct 15 '20 at 21:15
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    @gschenk That would be 27.5", not 27" – Noah Sutherland Oct 15 '20 at 21:46
  • I'm not certain if that distinction is always considered. 27" (630 mm) is rare now and almost obsolete in Europe. I've heard 585 mentioned as 27", without the .5. in conversation this makes sense since its half way between small MTB wheels 26" and large 28" wheels (622, 29er in US). What is more, 27" (630) with more than 25 mm width is somewhat unusual, especially as the OP mentions enormous 6 cm wide tyres. That would be a lot even for an old Rover or Omafiets style bike. – gschenk Oct 16 '20 at 12:42
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    @gschenk this is certainly an odd one, but for anything over about 584mm BSD 700c is your best bet (AKA 29" for the wide sizes) – Chris H Oct 16 '20 at 13:49

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