The truth about tire age

Yup, and the entire time I’ve been riding, folks have always cited five years as the expiration date. I’ve parroted it too: Once your buns hit 60 months, you should replace them regardless of their appearance because the rubber will have hardened and will have less traction. 

And yet, when I tried to substantiate the five-year rule of thumb, I couldn’t find any evidence for it outside the rider forums and word of mouth. Avon is the closest with a recommendation of seven years, but Bridgestone, Michelin, Dunlop, Continental and others actually list 10 years as the allowable service life for a properly maintained set of tires, which I have to admit, was a shock. I mean, a decade? Really!?  

Of course, most of us wear out tires in a year or two if not sooner, but I’ve certainly heard of people crying foul after buying “new” tires that were actually a few years old. Plus, I was curious. A few phone calls unearthed a set of Bridgestone RS10 hypersport tires from 2014 (Bridgestone used them as display tires in the demo truck they take to races and conventions) that I could test back-to-back with a fresh set of RS10s, since they’re still in production. 

I headed to Buttonwillow Raceway with “Dave,” our beater Suzuki GSX-R1000, and ripped around on the new tires (with date codes from 2020) to get familiar with their handling and establish hot pressures. Modern hypersport rubber is simply unreal, and in no time I was confidently riding nearly as quickly as I’m able. Fun stuff, but that wasn’t why we’d come to the track. 

Hesitantly, cautiously, I rolled out on the seven-year-old rubber. I was being extremely careful on my warmup lap, but after squirming around for a few turns like any new, cold tires would, the ancient RS10s came up to temp and felt just as grippy and agile as the fresh set. A few laps in, I was once again riding as hard as I pleased and with total confidence, this time on tires that were three quarters of the way through their shelf life, which was already 40 percent longer than I thought tires were good for. 

The reason our tires were still good is because they had been stored properly, and how tires are stored might be more important than how many months have passed since they were made. Age is not the same as aging. Think of milk: It’ll last for a week or more in the fridge, but if you leave it out on the counter overnight, well, you don’t want to lose that bet. 

It’s the same thing with tires. Stored indoors, out of direct sunlight and away from intense heat and other factors that we’re going to discuss, unused tires have a very long shelf life. And if you’re getting your rubber from a reputable shop or online retailer, they’ll have proper storage facilities and rotate stock to keep inventory fresh, so you’re very unlikely to encounter a tire that’s more than a few years old.  

But, say you have two or even three bikes and spread miles among them, or maybe you bought tires but don’t intend to use them right away. In both scenarios, tire age might become an issue.

At the core of it, tire aging is the consequence of two parallel processes. The rubber hardens due to the continued reaction of vulcanization ingredients in the material, and the molecular bonds within the rubber weaken, reducing the rubber’s elasticity and strength. Most people call this second aspect of tire aging dry rot, and it’s what causes cracks to form in the tread and sidewall of really old tires. 

This aging is an unavoidable and inevitable process, and there are five factors that contribute to the speed at which it progresses. Some you can control, some you can’t. 

Heat

Increased temperatures will accelerate the lingering vulcanization, so tires should be stored in a cool place like a basement or a ventilated warehouse as opposed to a sealed shed or a trailer. The ambient temperature is what it is, and, in hotter, sunnier climates like Arizona or Florida, tires will age faster than in cooler climates like Washington or New Hampshire. 

Once tires are in use, they’ll experience a lot more heat due to the friction created by rolling down the road. In the case of Dave’s RS10s, the carcass reached 175 degrees on track, and that kind of extreme heat cycling can cause a tire to harden quite quickly. Normal street tires don’t undergo such severe temperature swings, but every mile furthers vulcanization and catalyzes other adverse reactions within the rubber. 

Oxygen

Oxygen in the air causes atoms in the elastomer molecules to lose electrons. This oxidative degradation hardens and weakens the rubber. When tires are in service, they’re pumped full of air that’s 21 percent oxygen, so they’re basically pressurized with rubber poison. Filling your tires with nitrogen would eliminate this issue, but that’s pricey and tedious, and the rubber already has antioxidants mixed into the material, so it’s really not worth worrying about. If you’re really concerned about tires you’re storing, you can wrap them in a black trash bag to reduce exposure. The opaque plastic will also protect them from the next reactant, light. 

Light

Ultraviolet radiation causes homolytic fission, the fancy name for the breakdown of the elastomer molecules in the rubber into smaller, less stable pieces. The manufacturers mix UV-stabilizers into the rubber, but they get used up, so it’s important to store tires away from direct light. Once the tires are installed, parking your bike in the shade is going to be better for the tires than parking in the sun. As with the heat factor, sunnier climates mean tires will age faster, not only because of the UV radiation, but also because sun catalyzes the formation of ozone.

Ozone 

Ozone is a more reactant form of oxygen that wreaks havoc on rubber and is the leading cause of dry rot. In fact, concentrated ozone can trash a tire in as little as a year. 

Ground-level ozone is primarily formed when vehicle exhaust, gas vapor, and other chemicals react with sunlight and heat. Ozone is also produced when air is exposed to an electric arc, which means equipment like transformers and older appliances with brushed motors such as those found in fridges, compressors, and drills will kick off ozone, as well. So, if you have any suspect electronics where you park your bike or have been suckered into buying an ozone generator to purify the air in your house, it’s probably not doing your tires any good. 

Mechanical stress 

This is just the tire flexing, which is unavoidable when you ride on a tire but directly influenced by load, speed, and tire pressure. We’re not just talking about tread wear here, but also carcass flex that heats up and fatigues the rubber and more or less causes all the reactions we mentioned earlier to be accelerated. 

Heat, oxygen, light, ozone, and mechanical stress are all pretty easy to mitigate while tires are in storage, so even if a year or two or five passes as a tire sits on a rack, how much the tire actually ages will likely be imperceptible. I think we proved that with the RS10s. And once the tire is in use, just try not to park in the sun, near a furnace or hot pipes, or next to powerful electrical equipment. Better yet, just ride your damn bike enough to ensure you wear out the tread long before age is an issue. 

Even if people know they’ll roach their rubber in a summer, they want fresh product when they buy tires. I get it. Your best bet for getting the most recent date code is to buy what’s popular, since those models will have the highest turnover rate. On a site like RevZilla, that’s easy to figure out since you can filter by best sellers. Alternatively, purchase the latest and greatest; the newest model from a given manufacturer is, well, new. 

If you do end up getting suspect tires, or encounter rubber with an unknown history on, say, a used bike you’re buying, it’s important to check the date codes and visually inspect the tires for wear, damage and dry rot. You can also assess the rubber’s health by pressing your thumbnail into the tread surface. If it feels pliable and returns to its normal shape, odds are it’s still soft and resilient enough to provide adequate grip. (A more accurate approach is to invest in a durometer; most street rubber rates around 60 to 70 on the Shore A Hardness scale.) Plus, consider the tires’ intended use. Are you a casual commuter, or do you like to charge hard at the track? The more demanding the application, the more cautious I’d be with tire age. 

The bottom line is that tires don’t expire after five years. I know that may be hard to accept, given how prevalent the five-year recommendation is, but I was willing to have my mind changed and you should be, too. Of course I’m not saying that all older tires are as good as new, but we can all lighten up with concern for a tire’s age — if we’re confident in the way it was stored. 

But, if you have any concerns about the integrity of your tires, go ahead and replace them. They’re as critical to safety as your helmet, so if in doubt, swap them out. It’s always a good idea to start fresh, and now you know that “fresh” can apply to unused tires that are two, three, or even seven years old.