Tyre has a bulge or cut

A bulge (a raised lump on the sidewall or tread) means the cords inside the tyre are broken, usually from hitting a pothole or kerb. Air pressure is pushing out through the weak spot. A cut that reaches the cords is just as weak. Either can burst without warning.

Is it safe to ride?

No. Stop now. A bulged tyre can blow out, and a front blowout often causes a crash. Do not add more air. Push the bike or arrange transport.

Quick checks first

• Stop safely and look at the whole tyre, both sides.
• Is there a lump, or a cut with threads visible?
• Look at the rim next to the bulge: dented or cracked?
• With a tube tyre, a lump can also be the tube pushing through a cut.

Diagnose it step by step

1Is there a raised lump that you can feel, on the sidewall or tread?

• Yes: the tyre is finished. Do not ride. Replace a tyre. Go to step 4.
• No: go to step 2.

2Is there a cut? Open it gently with a fingernail. Can you see cords or threads?

• Yes: replace the tyre. Cuts to the cords cannot be plugged or patched safely.
• No, only a shallow surface cut in the tread: ride gently to have it checked, and check the tyre before each ride (Inspect tyres for wear and damage).

3Is the "bulge" really a wavy, uneven bead line next to the rim?

• Yes: the tyre is not seated on the rim. Deflate and have it reseated (Air leaking where the tyre meets the rim).
• No: treat it as a bulge (step 1).

4When the wheel is off, check the rim at the place of the impact. Dented, cracked or bent?

• Yes: go to Rim is dented or cracked. A new tyre on a damaged rim can fail too.
• No: check runout before fitting the new tyre (Check a wheel for runout).

5Did the impact also hit the fork or the steering?

• Yes, or unsure: after the new tyre is fitted, check the bars are straight and the bike runs straight (The bike has been dropped or crashed).

Causes, most likely first