Tyre Bulge (Tyre Bulge/Bubble)

A tyre bulge is a "red alert" indicating structural damage, meaning the internal cord plies (the tyre's structural skeleton) have ruptured. This poses an extreme safety hazard, as the bulged area is the weakest point on the tyre. Driven by internal air pressure, it can instantaneously blow out while driving, leading to a sudden loss of control.

Core Causes: Ruptured Cord Plies

The tyre sidewall is the thinnest section of a tyre, reinforced internally by only a few layers of cord plies (typically nylon or polyester cords). These cords can snap under the following circumstances:

Physical impact (most common): Hitting kerbs, deep potholes, or road debris at speed, or driving over speed bumps with insufficient tyre pressure. The sudden impact pinches the sidewall, causing the internal cords to be "sheared" against the rim edge.

Manufacturing defects: Poor bonding or misaligned layering of the cord plies during production (less common, typically isolated to a specific batch).

Extreme overheating: Running tyres on severely low pressure over extended periods, causing excessive sidewall flexing that leads to delamination between the internal rubber and cord plies (fatigue failure).

Risk Assessment: Never Take Chances

Location of bulge: Typically found on the sidewall. Regardless of its size or firmness, repairing it is strictly prohibited. 

Why can't it be repaired?

The sidewall undergoes the greatest amount of flex and deformation while in motion. No patch or filler material can ever restore the tensile strength of severed cord plies.

Any repair creates uneven structural stiffness, leading to dynamic wheel imbalance at higher speeds. Under load, the repaired spot remains highly prone to secondary delamination or sudden rupture.

Recommended action: Replace the tyre immediately upon detection. If you do not have a spare tyre, drive at a very low speed (preferably below 40 km/h) to the nearest tyre shop or workshop, and strictly avoid highway speeds.

Prevention Guide: How to Avoid It in Daily Driving?

Maintain correct tyre pressure: Under-inflated tyres have softer sidewalls. When hitting a pothole, the rim and the tarmac pinch the sidewall like a "sandwich", which is the primary cause of snapped cord plies. 

Avoid kerb strikes: Avoid grazing or scraping wheel rims against kerbstones when parking. Even if there is only a minor scuff on the outside, the internal cord plies may have already suffered pinch damage. 

Slow down before road hazards: Cultivate the habit of slowing down beforehand and tackling deep potholes or road humps at an angle to help disperse the impact force.

Editorial Perspective: How to Analyse Frequent Tyre Bulges?

When compiling car reviews or aftersales analyses, if you notice a particular vehicle model or factory-fitted tyre frequently suffering from bulges, consider investigating the following factors:

Impact of tyre profile (Aspect Ratio): If a vehicle comes factory-fitted with ultra-low-profile tyres (such as 35 or 40 series), the risk of cord ply failure multiplies over rough road conditions. This is often an inevitable trade-off when pursuing sporty handling and aesthetics. 

Sidewall stiffness design: Some "eco" or "comfort-oriented" tyres feature exceptionally soft sidewalls to reduce rolling resistance and road noise. On harsher road surfaces, their impact resistance is often weaker than that of stiffer, performance-focused tyres. 

Wheel rim design: Some alloy wheel designs have sharper outer lips or lack adequate chamfered edges, which can create a "guillotine-like" cutting effect on the tyre sidewall upon impact.

Practical editorial advice: As automotive journalists, if you identify that a test car's wheel-and-tyre package is susceptible to sidewall damage, always highlight the importance of proper tyre pressure management and road hazard awareness to owners in your review.