Repair guides › Wheels & Tires
Read tire and tube sizes
The tire gives grip and comfort; the tube inside holds the air. The tire bead hooks under the rim edge. Rim tape covers the spoke holes. Pressure is the biggest free upgrade on any bike: wider tires at lower pressure grip and roll better on rough ground; narrower and firmer is quicker on smooth pavement. Presta valves are thin with a lock nut; Schrader are car-style.
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Steps
- Find the size on the tire’s sidewall. Most tires show two: one like 700x40C (or 29x2.2), and the ISO size like 40-622.
- The ISO size is the one that matters: the first number is the width in mm (40), the second is the bead seat diameter (622). A tire fits when the second number matches your rim.
- 700c and 29" are both 622. 27.5" and 650b are 584. 26" is usually 559. Old 27" wheels are 630, which is not the same as 700c.
- The width must suit your rim’s inner width and leave room in the frame and fork (see Measure tire and chainring clearance).
- Tubes list a range, like 700x35–45C. Pick one whose range covers your tire width, with your valve type and a valve long enough for your rim.
- The pressure range is printed on the sidewall too (MIN–MAX). Enter it in My Bike so the app keeps your pressure inside it.
Diagram
Sliced across, like cutting through the tireTire, tube and rim
Signs it needs doing
- Flat (pinch flat = two little slits, "snakebite" = pressure too low)
- Cuts or threads showing
- Bulge in the sidewall (stop riding)
- Squared-off tread on the rear