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I am still learning, so for some things I still go to the bike repair shop. I was heading there and my tire deflated, so I was like "Ok, I am nearly there, so I'll have him patch that and save me the bother."

He then told me that it was not a puncture but a "scratch," and that it was because the tires are getting worn from the inside. That surprised me. I knew that tires get worn from the outside, but, from the inside???

I agreed for him to get me some tires, as it was something he had bought for another customer that never came back for them and he was giving them to me at 60% of the price, but I feel like he is just trying to sell me stuff for the sake of it and it just happened to be that I wanted to change tires.

Is that a thing? Wear from the inside?

(I mean, I used to go to another shop, but it is five-times farther away from this one. So when this shop opened up, I decided to switch to the closer one. But when I last asked the previous shop about my tires, they told me my tires were half life, and I wouldn't need a change until they worn a bit more, maybe six more months and that was just two months ago, in which I have used the bike maybe 20 mins a day, with the exception of a 60 km round trip last week)

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    All good comments so far. In addition, you mentioned changing shops due to location/distance to the shop, which is a valid reason. A local bike shop (LBS) relationship is similar to that of an auto shop relationship. You build trust with them and if they are trustworthy, they treat you right, getting you good, timely service at a fair price - without gouging you. That said, your new, closer LBS could be giving you a legitimate assessment on your tire(s). You might get a second opinion from your more distant LBS, but even then, be wary of their opinion of their new competition.
    – Ted Hohl
    Aug 19, 2022 at 18:05
  • @TedHohl Tangential: I've never been a fan of the shop loyalty thing. Nobody's gonna remember you if you bring your car in once a year for an oil change; It's even worse with cycling where 90+% of repairs that make financial sense can either be done at home or require such specific tools/knowledge that 1/100 shops might be able to help (e.g. threaded BB shell tapping). If a business charged me more on the sole premise that I'm a new customer, I'd be weary of that business in the future.
    – jayded-bee
    Aug 19, 2022 at 18:12
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    Answers go in the Answers section - comment are for clarifying and improving the question Consider reposting these as answers, please.
    – Criggie
    Aug 19, 2022 at 23:18
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    @Criggie Sorry, I'm never sure if my rambling makes sense to post as an answer. Thanks for looking out for me :)
    – jayded-bee
    Aug 20, 2022 at 9:21
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    @TedHohl I'm afraid the staff at the LBSs around me has too fast a turnaround for me to get to know them, while the older guys groan when they see me, knowing the task I have for them is going to be a PITA (else I'd have solved it myself). Perhaps this is a difference in area/culture.
    – jayded-bee
    Aug 20, 2022 at 9:24

4 Answers 4

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There are a few ways to get a tube punctured. You can get a piece of glass or similar material into the tire, and that will eventually puncture the tube as it works it’s way through the tread. You could have the side of the tire hit something sharp or jagged, which will tear the tire and instantly deflate the tube. You could pinch flat, which is when you hit the edge of a pothole hard enough to force the tube outside the tire bead. That causes a snakebite-like pair of slitted holes on the inside surface of the tube. Apart from pinch flats, I can’t think of a way that the tire could have been damaged from inside the tire without the tire not also getting punctured.

It’s possible the mechanic is using very unusual phraseology or that they are operating on a very unusual mental model of how the world works. Alternatively, if the conversation didn’t take place in English, it’s possible that he used a colloquial phrase that actually describes one of the mechanisms above but that you didn’t understand (this is not a criticism, there is always specialized terminology that’s confusing to outsiders).

If the mechanic said “scratch” or similar, I would normally think that the tire got gashed on a sharp object, tearing a hole that’s usually on the side of the tire. In English, “wear” for tires usually means that the tread gets abraded away as the tire rolls on the road surface. There definitely isn’t a similar process going on inside the tire. The mechanic hopefully meant something else, or else he does not know how tires work. Perhaps he meant that you had picked up a bit of glass in the tire that eventually punctured it?

The above wouldn’t be a reason to replace the tire by itself. It can be hard to tell when a tire is worn out. Some tires have wear indicators molded into them, which disappear when the tread is worn out. Without them, you can roughly tell by visual appearance, plus the rear tire gets visibly squared off. If the tire is a knobby tire, the knobs should be visibly worn.

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  • I could see a term like"wear" being appropriate if something had "worn through" the tyre. That would normally not require replacement but it's possible.
    – Chris H
    Aug 20, 2022 at 8:56
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    Another way for the tube to get punctured is if the spoke ends stick through, but in that case you should replace the rim tape (or use spokes with a shorter length). Yet another way is small burrs in the rim which can be fixed with sandpaper.
    – Michael
    Aug 20, 2022 at 10:03
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The tire can get damaged from the inside if there is debris inside. If it's a particularly poorly manufactured, or just used or old, then damage to the carcass is also possible due to merely being inflated.

This is a great opportunity for you to learn how to take the tire and tube off and check for yourself; A roadside tube swap shouldn't take you more than 15 minutes (unless your tire is particularly stubborn, stretched, old, cheap). Tubes and tires can be patched, too, if the damage is small enough. If you have some extra time, this is also possible on the side of the road, though most people I know would swap the tube to get on their way quickly, then patch the old tube at home.

Not having inspected the tire yourself, your description of the damage is obviously of no use to a third party (this forum's readers). What the mechanic's actual goal was is anyone's guess; Maybe he's telling the truth, or maybe you got suckered into buying something you didn't need. Good (car/bike) mechanics have always given me the parts they've replaced so I could inspect them for myself -- I paid for the new part, and I already owned the old one. Letting the owner inspect the replaced part is a good policy, in my opinion. That is to say, you could have asked to take the tire home, especially if you had doubts.

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I have had a tyre wear out on the inside and cause punctures before the outside was worn out, but on a well-used back tyre. I think it was a Schwalbe Marathon Supreme, but I've tried a few tyres on that bike over the years.

The symptom was that after about 150km or 100 miles I'd get a slow puncture. I eventually tracked it down to a thread of the tyre coming through the inner rubber and abrading a spot on the tube.

So it's possible, but it might not be the situation you've got.

In general though, back tyres wear much faster than front, and a shop advising you to change both after fairly light use means I'd be wary of trusting them at all.

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  • "I eventually tracked it down to a thread of the tyre coming through the inner rubber and abrading a spot on the tube." The threads are pretty soft fabric, I find this highly unlikely.
    – Michael
    Aug 20, 2022 at 10:01
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    @Michael it was the exact spot, repeatably. I align the logo to the valve and checked 3 tubes. And the thread I found felt fairly soft, not like a bit of wire that had worked through, but must have had just enough edge to abrade slowly.
    – Chris H
    Aug 20, 2022 at 10:07
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Per recommendation, posting as an answer:

You mentioned changing shops due to location/distance to the shop, which is a valid reason. Convenience is a big driver in your decision, but it is not the only one.

A local bike shop (LBS) relationship is similar to that of an auto shop relationship. You build trust with them and if they are trustworthy, they treat you right, getting you good, timely service at a fair price - without gouging you. You reciprocate by bringing business to them; you own business and referrals to the business for others looking for similar service.

That said, your new, closer LBS could be giving you a legitimate assessment on your tire(s). You might get a second opinion from your more distant LBS, but even then, be wary of their opinion of their new competition. There is a human element in play here, which is nothing new.

Any relationships you build and develop with a LBS takes time. It might be quicker with a smaller shop as they may have more time to converse. A larger, busier shop can be more intimidating to some, but if they want your business, they should at least get to know you and your needs. That is how they can serve you. If you don't feel comfortable with one, then try another.

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