Is an Old Tire Safe to Ride?

What determines degradation in a tire's quality over time, and how much is too much?

Dear Lennard,

Hey, I have a simple question (I hope). Can I use old but but unused bike tires? With car tires, you are supposed to change them after six years regardless of how few miles you put on them. But I've read stories of bike riders aging their sew-ups for years. I have a few leftover Conti Force tires. They used to come in paired with the Attack front tire (quite narrow). The Force tire was supposed to be used in the rear, but like others, I used them front and back. They are similar to the Conti GP5000s 700x25mm, but they are slightly bigger and mount easier. My Force tires are getting up around the six year limit for car tires, so I am wondering if they are still safe to ride. Your thoughts?

Michael

Dear Michael,

This is a great question. Indeed, car tires are supposed be replaced after six years.

While heavy use of a tire obviously wears it down and shortens its life, occasionally driving on a car tire that is otherwise sitting on a car that doesn’t get used lengthens its life. There is a famous car collection here that has employees who drive every car at least nine miles every month or so to minimize deterioration of the tires. Also, “flat spotting”can occur if tires are left for long periods with the weight of the car on them.

Car tires have antiozonants, waxes, antioxidants, and other substances in their rubber compound that protect them from exposure to the air, and I understand that they must be flexed to squeeze critical protectants out to the surface and keep them actively working. If the tire just sits, the protectants eventually disappear from the surface, allowing ozone, which breaks bonds inside elastomer molecules, to attack the rubber. This is worse if stored next to electric motors, since they produce ozone (air compressors and drills are often kept near stored cars and bikes).

This paper entitled The Pneumatic Tire put out by the US. Department of Transportation National Highway Traffic Safety Administration details the dangers to tires from ozone, atmospheric oxygen, heat (causing “additional vulcanization” hardening them more), weathering (irradiation by UV light).

As you alluded to, we all learned when we were racing on tubular tires (“sew-ups”, as you called them) that for best results we should put them on a rim and leave them to “age” for “years” before using them. We were regaled with legendary stories of how Ernesto Colnago would age Eddie Merckx’s tires before he raced on them.

Unlike “sew-ups” and similar to car tires, molded clincher tires are vulcanized during the molding process. In contrast, handmade tubular tires only have vulcanized tread strips, while the tire carcass is generally only brushed with liquid latex and not vulcanized. (Vulcanization is the process of hardening rubber, usually with sulfur and heat.)

I ran your question by representatives of lots of bike tire companies. Here are responses from Challenge, Specialized, Maxxis, Schwalbe, FMB, and Pirelli to how long an unused bicycle tire could be stored and still used safely, as well as past responses I’ve gotten to a related question of tire storage from Michelin, Continental, Hutchinson, and Ritchey.

― Lennard

From Challenge:

“Aging tubulars is correct methodology, but we are talking about tubulars and handmade production where materials are all natural. These include latex, rubber-base glues, cotton, silk, polyester, and the absence of vulcanization.

The tubular tire is assembled with these materials and requires a drying time or “cure” time. This process is also called “Cold Vulcanization”. The construction reaches its maximum strength in bonding after X amount of time. A tubular needs at least 30 days of aging before use.

The aging in cellars for 1 or 2 years for these products is optimum. Even longer periods than this, we have seen in CX, with Wout [Van Aert] and others using old tubulars with Michelin mud tread. Those had to have been stored for some years (at least 5). It depends on how the product is kept.

Generally, it is quite visible if the tire is not suitable for riding. Coatings on tubulars were non-existent, so weak casing and treads would be visible: tread hardened and visible cracking.

Nylon tires are another world. The construction is based on rubber, and the use of synthetic rubber is a large part of the tire. The aging process in these tires is not required, and the bonding of all the components is done by vulcanization, which bonds all components together by heat. Once this tire is pulled out of the mold, the process is finished, and the tire can be used immediately.