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I work at a community organization that receives a lot of donations, including tires, in various condition. We inspect tires for obvious damage and wear, and signs of aging like hardening or cracking. Are there non-obvious reasons to be wary of donated rubber that looks fine, just a little old?

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    Nice, donating tires. My policy is to replace a tire before it gets punctured, I hate it to switch a tire at the side of the road. I'm not in Boston, otherwise I'd be happy to send you my old tires. Keep up the good work!
    – Christine
    Sep 27, 2022 at 8:37
  • We receive a lot of nice, usable stuff in every category of component and accessory. There may be a bike co-op or bike kitchen near you that can accept donations! I'm finding the bicycling community to be quite generous. In fact, we could use a few more wrenches on the staff!
    – SamA
    Sep 28, 2022 at 13:13
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    Did anyone else see the title and think someone was thinking of stopping using tyres at all? Sep 28, 2022 at 15:00
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    @Criggie I added a tag "bike-coop." Thanks for the suggestion!
    – SamA
    Sep 29, 2022 at 14:24
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    @Criggie is this really a relevant tag for this question? I mean, the question of when a tire gets too old is not really depending on whether it's for a bike-coop or not. Sep 29, 2022 at 22:41

4 Answers 4

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This is a great question and there are actually some good ways of approaching it.

Inconveniently, you need to see the tire installed and inflated to have high certainty that it's good for reuse. Until then, there could be casing issues (bulging, cracking that's worse than it looks deflated, distortion, etc) that aren't apparent when it's just a loose tire.

However, there are heuristics you can exploit that allow you to do some pretty good screening even on loose tires.

For commercial shops that save unwanted used parts and donate them to community shops or bike projects, a very common scenario is a customer that has a pair of old tires on their bike and wants to start fresh with two new ones. It is overwhelmingly common in this case that the rear is toast and the front still has life left. On the bike, the most direct symptoms to observe are the roundness profile at the contact patch. Worn out tires get pretty squared off, and if the front one was the same age you often have a good visual comparison between still-pretty-close-to-original in profile versus worn. (There is a tangential conversation here about the merits of rotating tires on bikes, but that is a religious question and most people don't do it so we'll leave it at that).

If you're presented with two of the same tire and one is way less worn down the middle, it's pretty likely it was a matched pair, the rear eventually started flatting or having other issues or was just worn out, and the front is still usable. For that situation, throw away the more worn one and give the other a shot.

Where it could be murkier is when whoever donates you the tires has done you the favor of already throwing away the rear and only giving you the front. There are pretty good odds that if it's a tire that seems weathered but not all that worn on the contact patch and with no other apparent issues, that is what's going on.

Another approach is observing the thickness of the middle of the tire compared to the adjacent areas, where it's reasonably assumable that the starting thickness was the same as the middle. If the contact patch is a lot thinner than the tread areas that started at the same thickness, the tire is probably toast.

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    This is an excellent set of practical advice for evaluating used tires. Thanks.
    – SamA
    Sep 28, 2022 at 1:43
  • It's very important to ensure your front tyre is in good condition, if that fails then injury is pretty much inevitable whereas if the rear fails you are more likely to be able to stop safely. That's not to say the rear tyre condition isn't important.
    – John Hunt
    Sep 29, 2022 at 9:56
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For reference - tire parts names.
enter image description here
The "Anti-puncture strip" and "bead protection tape" are not found on most tires.
Bead, casing, sidewall, and tread are the most common components.

Worn tread is easy to spot.

Here are some pictures - things to look for in tires to evaluate if they need replacement:

Tire bubble - caused by a torn tire casing under the tread.
Often the tire must be inflated to find this issue. enter image description here

enter image description here
Caused by a torn casing and sidewall at the bead allowing the sidewall to separate from the bead. Usually this issue can be found without inflating the tire.

enter image description here
Split tire - usually can be found without inflation

Dry rot
enter image description here
Time and sun are not kind to tires. This is an example of dry rot caused by oxidation and UV on both gum wall and black wall tires.
Dry rot makes a tire "crunchy" it loses it's flexibility and becomes brittle so that the casing, sidewall or tread can break allowing the tube to come through or the bead to separate.

You can feel dry rot with your hands by flexing the tire. A tire should be flexible. Sometimes you can actually hear the tire make crunching sounds as flexing breaks casing threads and makes tread crackle.

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  • Thank you for these illustrated references!
    – SamA
    Sep 29, 2022 at 2:45
  • If you see anything like the above photos, please dispose/recycle the tyre!
    – John Hunt
    Sep 29, 2022 at 9:57
  • Excellent illustration, but readers should remember that tires in this condition are well past prime.
    – Weiwen Ng
    May 5, 2023 at 1:42
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This is tough to answer as it'll be different for different types of tires.

For my riding styles, a tire is shot when the side walls won't stop weeping (all bikes), when the knobs stop hooking up (MTB), or when punctures/gushers/flats are becoming increasingly common (road, commuting).

Weeping sidewalls might be apparent in a donated tire, but probably not. Roached knobs aren't an issue if the tire is going on a beater/around-town bike that simply needs to roll for someone on a tight budget.

But the increasingly common flats/punctures angle is really what counts. For that, I would try to qualitatively gauge the thickness of the non-knobby tread and make a judgement call based on my gut feeling. For the types of bikes I've helped build at a community center, I'd be pretty quick to throw out worn, non-rugged tires.

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    I suspect a community organization will rely on old school tubes, so the weeping be a concern.
    – mattnz
    Sep 27, 2022 at 3:24
  • @mattnz yes and no. In a MTB tire's case, to me the weeping is indicative that the side wall has taken some non-catastrophic damage, likely on Oregon chunky and sharp basalt
    – Paul H
    Sep 27, 2022 at 3:26
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    @PaulH that sort of minor wear and tear on the sidewalls of an MTB tyre won't be enough to stop it lasting a long time with a tube
    – Chris H
    Sep 27, 2022 at 15:03
  • Is "weeping" a phenomenon of tubeless setups?
    – SamA
    Sep 28, 2022 at 1:38
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    @SamA yes. Sealant (or some component of it) eventually consistently pushes through the sidewall in a well-used tire subject to rocky terrain
    – Paul H
    Sep 28, 2022 at 16:54
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Short answer - if you wouldn't feel safe riding on the tyre yourself on a high-speed descent, then it is for the bin.

Add a mental safety-factor/margin of error of 20% and don't be hesitant to say "no thanks" to donations that don't meet the grade. You don't want to become the dumping ground for literal rubbish at your group's expense.

Err on the side of caution - there's always more tyres in the donation stream.

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    It's hard to give volunteers and trainees subjective criteria like the first, as personal experience varies. But yes, we certainly can afford to be (and have some duty to be) choosy about what we put on the floor or onto someone's bike.
    – SamA
    Sep 29, 2022 at 2:43
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    @SamA understood. Back when I was involved with a community group, there was one single qualified guy who handled classifying incoming bikes for repair or as parts donors. That way the consistency was there. The donors were stripped down as far as possible and all reusable parts were cleaned, bagged and sorted. Leftovers were sorted to steel/aluminium/brass/general waste. Repair bikes were given to the larger group of volunteers to learn-on. Finally a two person team did a safety inspection before putting the completed bike in the "ready to go" store. It was fairly well delineated.
    – Criggie
    Sep 29, 2022 at 9:32

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