5 Warning Signs Your Tyres Need Replacing (That Aren’t Tread Depth)
Although tyre tread depth is the classic metric everyone talks about when it comes to replacing your tyres, it’s only one piece of the safety puzzle. Your tyres can be at the legal limit and still pose a serious risk due to issues you might not even be aware of.
In New Zealand, the minimum legal tread depth for your tyres is 1.5mm. While the 20c coin test is a handy way to check your tread, the tyres on your car are subject to much more stress than just simple tread wear and tear. Ignoring the structural and age-related signs of tyre wear can be dangerous, as these issues can lead to tyre failure, sudden blowouts, or even indicate underlying mechanical problems that may compromise safety or result in a failed WOF.
To keep you and your passengers safe on the road, you need to know the hidden dangers that signal it’s time for an upgrade. So, what are the five most critical non-tread warning signs that mean it’s time to replace your tyres? Let’s take a look below.
1. Sidewall Cracks
The sidewall is the most flexible part of the tyre and the first to show signs of age or environmental damage. Sidewall cracking are breaks that appear on the vertical side portion of the rubber tyre, they are a common sign that the rubber compound is breaking down or deteriorating.
· What It Looks Like: Fine lines, splits, or spider-web cracking (sometimes called “crazing”) appearing on the smooth rubber of the sidewall. In severe cases, pieces of rubber look dried out or start to flake away. They are most noticeable on the sidewall because it undergoes a great deal of flexing and is often the most exposed to the elements.
· What It Means: Commonly called perishing, weathering or dry rot, sidewall cracks occur as a result of the natural degradation of the rubber compounds, which are designed to keep the material flexible. Sidewall cracks most commonly occur due to age, excessive underinflation and continued UV exposure (common in NZ’s harsh sun), but frequent cycles of expansion (heat) and contraction (cold) can also stress the rubber, leading to premature cracking.
· Safety Risk: These cracks compromise the structural integrity of the tyre, making it brittle and highly susceptible to a sudden blowout under load or impact. Deep or widespread perishing will also result in a failed WOF.
· Action: If you notice cracks on your tyre sidewalls that are anything more than faint, shallow lines, you should have the tyre inspected immediately by a qualified professional. Sidewall damage cannot be safely repaired, when the structural integrity is compromised, the tyre must be replaced.
2. Bulges Or Bubbles On The Sidewall
A tyre bulge is essentially an air pocket that has formed beneath the outer layer of rubber. When the inner plies are broken, the air pressure from inside the tyre pushes out into the gap between the internal structure and the outermost rubber layer, causing the visible bulge. A bulge is probably the most serious and dangerous warning sign for all tyres.
· What It Looks Like: A visible outward protrusion or bubble on the sidewall, often about the size of a golf ball or egg or smaller.
· What It Means: A bulge means the internal structure of the tyre (the fabric or steel cords) has been broken or severed. This usually occurs when hitting a pothole, kerb, or road debris. This means the internal air pressure is now pressing directly against a single layer of rubber (which could instantly rupture at any time).
· Safety Risk: A sidewall bulge is an imminent blow-out just waiting to happen, particularly at high speeds on the motorway or under heavy braking. It is irreparable damage and makes the car instantly unsafe to drive.
· Action: Stop driving on the tyre immediately and replace it
Exposed cords/plies or fabric means that the tyre has worn down or been damaged so severely that the reinforcing structural layers beneath the rubber tread or sidewall are visible. These are the foundational structural elements that contain the air pressure and handle the stresses of driving. If this is the case, your tyre is definitely at a critical failure point. Although it is very uncommon for a tyre to get to this point without unusual circumstances.
· What It Looks Like: You can see the internal metallic wires or light-coloured, usually white or yellowish, nylon threads or fabric woven tightly together showing through the rubber anywhere on the tyre (tread or sidewall).
· What It Means: This indicates that the rubber has been worn away entirely past the legal tread depth and into the internal layers. This could be due to excessive wear (a bald tyre), alignment issues, physical damage due to extreme impact or a suspension component failure. The only thing containing the inflated pressure is the cord structure, which could fail rapidly.
· Safety Risk: Stop driving immediately. Your tyre is compromised and at severe risk of a blowout and loss of traction.
· Action: If you see any cords or fabric exposed on your tyre, you must stop driving immediately. Do not attempt to drive, even to the nearest repair shop, unless you have installed your spare tyre first. The tyre will need to be replaced, and in the case of uneven wear, your vehicle should also be inspected for underlying alignment or suspension issues.
4. Severe And Uneven Wear Patterns
Any deviation from the expected, gradual, and uniform wearing down of the tread across the entire surface of the tyre is considered an uneven wear pattern. Uneven wear is often a clear indicator of an underlying mechanical problem with the vehicle or an issue with tyre maintenance. Ignoring these patterns is dangerous because the tread is reduced in critical areas, severely compromising your traction, handling, and stopping ability.
Edge Wear (Both Edges)
- What It Looks Like: The shoulders wear down fast, leaving the centre deeper.
- What It Means: Likely due to severe under-inflation, where the soft side walls are carrying too much load.
- Action: Check your PSI when the tyres are cold and inflate to the manufacturer’s specification.
Centre Wear
- What It Looks Like: The middle of the tread wears down faster than the edges.
- What It Means: Likely due to severe over-inflation, where the crown of the tyre is being overworked.
- Action: Check your PSI and deflate to the correct specification.
Feathering / Scalloping
- What It Looks Like: Tread blocks are worn diagonally or one side of the tread feels sharp when running your hand over it.
- What It Means: Likely a wheel alignment or suspension fault. Often caused by incorrect Toe setting (alignment) or worn shock absorbers/struts that cause the wheel to bounce or “scrub.”
- Action: Immediate wheel alignment check and suspension inspection.
Cupping Or Scalloping
- What It Looks Like: Scoop-like, wavy, or scalloped dips appear around the tire’s circumference, creating patches of worn and unworn areas.
- What It Means: The suspension is failing to keep the tyre firmly on the road, causing it to bounce or hop. This leads to vibration, excessive road noise, and highly unpredictable traction.
- Action: Immediate wheel alignment check and suspension inspection.
Excessive Age (The 6-Year Rule)
Like all things, tyres have a limited lifespan. This is regardless of how few kilometres they have travelled or how well you drive.
- How To Check: Look for the four-digit DOT code on the sidewall of your tyre. The last four digits indicate the week and year of manufacture (e.g. 2825 means the 28th week of 2025).
- What It Means: Over time, tyre rubber degrades and hardens, even if the car sits in a garage. This hardened rubber dramatically reduces grip, especially in wet weather, and increases the likelihood of perishing and internal damage.
- Action: Many manufacturers and experts recommend replacing tyres that are 6 years or older, and the absolute maximum is typically 10 years.
If you observe any of these five signs of tyre wear, do not wait for your next WOF. At Mag & Turbo NZ, we offer professional, no-obligation tyre inspections. We can quickly diagnose any issues, check your wheel alignment, and provide safe, reliable replacement options to get you back on the road! Book your vehicle in today!
