Cycling

How to Read Your Bicycle Tyre Size: 27.5 x 2.10, 700x25c and 55-584 Explained (India)

Decode the numbers on your bicycle tyre: inches, 700c and ETRTO sizing, how to match tubes and valves, with tyres and tubes in stock in India.

Instasport

— 3 min read
Ortem Trek King 27.5 x 2.10 bicycle tyre wire bead

How to read a bicycle tyre size: 27.5 x 2.10, 700x25c and 55-584 explained

If you have ever stared at the side of your bicycle tyre and wondered what "27.5 x 2.10" or "55-584" means, you are not alone. Tyre sizing mixes inches, millimetres and old French sizes, and getting it wrong means buying the wrong tyre or tube. This guide decodes the numbers on your tyre sidewall and shows how to pick a matching tube, with options in stock at InstaSport.

The three sizing systems you will see

1. Inch sizes (for example 27.5 x 2.10). The first number is the approximate outer diameter of the tyre and the second is the tyre width, both in inches. MTBs and many city bikes use this format. A 27.5 x 2.10 tyre fits a 27.5-inch wheel and is 2.10 inches wide. The 27.5-inch size is also called 650B.

2. French sizes (for example 700x25c). Road and hybrid bikes use 700c wheels. The 700 is the approximate diameter in millimetres, and 25 is the tyre width in millimetres. The letter c is a legacy designation.

3. ETRTO (for example 55-584). This is the most accurate system. The first number is the tyre width in millimetres and the second is the bead seat diameter in millimetres, which must match your rim. So 55-584 means 55 mm wide on a 584 mm rim, which is the 27.5-inch (650B) size. A 25-622 tyre is 25 mm wide on a 622 mm rim, the 700c size.

Why ETRTO is the number to trust

Two tyres can both say "26 inch" and still not fit the same rim, because older systems are not consistent. The bead seat diameter in ETRTO tells you exactly. When ordering a replacement, match the second number (the rim diameter) first, and then pick a width the rim supports.

Matching the right inner tube

  • Wheel diameter: The tube must be made for your wheel size, for example 27.5 inch for a 27.5 tyre.
  • Width range: Tubes are sold for a range, such as 1.75 to 2.35 inch. Your tyre width should fall within that range.
  • Valve type: Presta (thin, with a small lock nut) or Schrader (the same valve as a car or motorcycle). Your rim's valve hole decides which you can use. See our Presta vs Schrader guide.
  • Valve length: Deeper rims need a longer valve. 48 mm is a common length for standard rims.

Tyres and tubes available at InstaSport

For a 27.5-inch MTB, the ORTEM TREK KING 27.5x2.10 (55-584) Wire Bead tyre is ₹1,213. Matching tubes include the Panaracer StAndard Tube 27.5 x 1.75-2.35 Schrader 48mm at ₹480 and the Panaracer StAndard Tube 27.5 x 1.75-2.35 Presta 48mm at ₹495. The 2.10 inch width fits inside the 1.75 to 2.35 range of these tubes. For a road or hybrid bike, the ORTEM M750 700x25c (25-622) Wire Bead is ₹998. If your bike runs 26-inch wheels, note that the Ortem Butyl Tube 26 x 1.75-2.20c 48mm Presta at ₹413 is for 26-inch wheels and will not fit 27.5 wheels.

Quick checklist before you buy

  1. Read the ETRTO number on your current tyre.
  2. Note the valve type on your current tube or rim.
  3. Pick a replacement tyre with the same rim diameter (the second ETRTO number).
  4. Choose a tube that covers your tyre width and has the right valve and length.
  5. Replace tyre and tube together if both are worn. Our tyre buying guide has more advice.

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Frequently asked questions

What does 27.5 x 2.10 mean on a bicycle tyre?

It means the tyre fits a 27.5-inch (650B) wheel and is 2.10 inches wide. The ETRTO equivalent is about 55-584.

What does ETRTO 55-584 mean?

The first number, 55, is the tyre width in millimetres. The second, 584, is the bead seat diameter in millimetres, which must match your rim.

Can I use a 26-inch tube on a 27.5-inch wheel?

No. The tube must match the wheel diameter. A 26-inch tube is too small for a 27.5-inch wheel.

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