What Is Tire Dry Rot and When Is a Tire Too Old?

Dry rot is cracking in the rubber caused by age and bad storage. It shows up as fine cracks between the tread blocks and along the sidewall. Once a tire is dry rotting we recommend replacing it, and past five years old we treat age as the deciding factor regardless of tread.

It is the check that decides whether a set is worth changing over again. This is the one that surprises people who take care of their vehicles. Plenty of tread left, barely driven, and the tire is finished anyway.

What causes tire dry rot?

Two things: time, and storage conditions. Rubber loses its oils and flexibility as it ages, and heat, moisture, and sunlight all speed that up. A set stored badly over the summer can come out worse than a set that was driven.

Dry rot happens when a tire is stored improperly, either in heat or in a damp environment. It also happens simply because the tire is old, and usually tires older than five years count as old tires. If they are starting to dry rot we recommend replacing them as soon as possible. This is why we tell every customer to check the year on the tire every single time. People look at the tread and stop there, and the tread can be fine while the rubber underneath it is already going.

What makes it worse

• Heat. A hot shed or a garage that bakes all summer
• Moisture. Damp storage, or tires sitting on a wet floor
• Sunlight. UV breaks the compound down directly
• Time. It happens to every tire eventually, driven or not

Cracking isn't always terminal though: ask whether a repair is still possible before writing the tire off.

Note that we do not offer tire storage, so where your off-season set lives is your call. Cool, dry, and out of direct sun is the target.

How do you spot dry rot?

Look for fine cracks in the grooves between the tread blocks, cracking along the sidewall, and a surface that looks chalky or faded rather than dark. Run a hand over it. Healthy rubber has some give, and dry rotted rubber feels hard.

Where to look, in order

1. Between the tread blocks. The grooves flex most, so cracks often start there
2. The sidewall, especially near the bead where the tire meets the rim
3. The inner sidewall. Same problem as inside-edge wear, it hides on the face you never see
4. Overall colour and texture. Chalky and grey rather than black

How bad is bad?

How do you read a tire's build date?

Find the DOT code on the sidewall. The last four digits are the week and year the tire was built. 3223 means the 32nd week of 2023. The code is moulded into one side only, and it is not always the outward-facing side.

Why five years is our line

Past five years, the compound has hardened enough that it changes how the tire performs, and dry rot becomes likely rather than possible. That holds even for a tire with most of its tread left. It is the single check that catches the most surprises, and almost nobody does it.

This matters most on:

• Winter tires, because winter grip depends on a soft compound in the first place. See when winter tires are worn out
• Spare tires, which sit untouched for years and are needed on the worst day
• Low mileage vehicles, where the tread lasts far longer than the rubber does
• Used tires, which can be older than the buyer assumes

That's exactly why a winter set nearing the end of its life is worth swapping out proactively: see the replacement timeline explained on our Fredericton winter page.

Will dry rotted tires fail an inspection?

New Brunswick's inspection manual has a specific criterion for this. A tire is rejected if it is cut or weather cracked in excess of approximately 2.5 cm, about 1 inch, in any direction, or cracked to the point of exposing the tire cords. That is the dry rot criterion, and it applies no matter how much tread is left.

The manual also rejects a tire for cord damage or ply separation causing any bump or bulge, a separate failure from dry rot.

Source: New Brunswick Official Vehicle Inspection Station Manual

If dry rot means the whole set is due, what the replacement fitting costs in Fredericton is public before you book.

Getting it checked before an inspection costs less than finding out during one. We do tire work only, not inspections, but we will look at your set and tell you where it stands.

Key takeaways

• Dry rot is the rubber compound breaking down from age and bad storage.
• Look for fine cracks in the tread grooves and along both sidewalls.
• The last four digits of the DOT code are the build week and year.
• Past five years, treat age as the deciding factor regardless of tread.
• It cannot be repaired. A dry rotted tire gets replaced.
• Spares and low mileage vehicles are where this hides longest.

Frequently asked questions

How do I know how old my tires are? The last four digits of the DOT code on the sidewall are the build week and year. A tire stamped 3223 was built in the 32nd week of 2023. The code is moulded into one side of the tire and it is not always the side facing out, so check both.

Is it safe to drive on dry rotted tires? Not once the cracking is real. Dry rot means the rubber has lost flexibility, and a tire that cannot flex properly is a tire that can fail under load or heat. Fine surface cracking is a warning. Deep cracks are the end of that tire.

Can dry rot be repaired? No. Dry rot is the rubber compound itself breaking down, not a puncture in an otherwise good tire. There is nothing to patch. The only fix is replacement.

Do tires expire even if I do not drive on them? Yes. Rubber ages whether the tire is on a vehicle or sitting in a garage. A spare that has never touched the road can still be dry rotted. Heat, moisture, and sunlight all speed it up.