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I have 20 x 3.0"tires, which seem to be pretty hard to find--especially with nice puncture-resistance like Schwalbe's "Smart Guard," or something of that nature. Unfortunately, I'm definitely getting more flats.
My mechanic told me that I could double up on the tires--put old tires underneath the new ones so that it forms essentially an inner tire liner. He did this in the good old days, apparently. He in fact recommended that over other commercial products (Tire Liners) because apparently Tire Liners cause flats in themselves.
I have an e-bike, so I wouldn't mind the extra weight and might give it a try, but was wondering if anyone still does this today and if there's anything I should be wary of when / if I try it out?

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    I've heard of the opposite: Cut the bead off an old tire and then stuff the new tire inside it. (In fact, Henry Ford did this on his first automobile.) You'd have trouble stuffing one tire inside another while still getting the bead of the outer tire to fit on the rim. – Daniel R Hicks Feb 12 at 22:44
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    @DanielRHicks if you were to use a more narrow tire for the 'inner tire' and put the wider (3") tire over top of I think you should be able to get the bead of the 'outer tire' to seat properly. However the added ridge from the 'inner tire' might cause the inner tube to be pinched and in this way cause punctures.. you'd have to try to be sure. For this reason DanielRHick's suggestion might be a better alternative.. – Maarten -Monica for president Feb 12 at 22:53
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    What brand is your current tyre? Can you confirm the ETRTO measurement off the sidewall of the tyre ? – Criggie Feb 14 at 3:09
  • Kenda Flame 68-406 stamped on them-- they're on 40mm wide federal stance xl rims if that provides any insight.. – begs-the-hessian Feb 14 at 17:04
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I'd just buy tyre liners (example from Zefal). They're made from tough polyurethane which many sharp things won't get through or at least not quickly. I've used cheap (unbranded eBay) ones on a cheap bike when I didn't want to buy expensive new tyres, and they worked well, with one issue, probably what your mechanic was thinking of that was easily solved by taping over the end. They can be cut down to fit your small wheel, and it looks like the ones I've linked are made wide enough. Another popular brand is Mr Tuffy, though I've never used them.

If you want to try recycling instead of buying, then use the tyre liners as inspiration. Here's Zefal's video on fitting them, so you can see the approximate proportions.

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This sounds like one of those ridiculous old-time ideas that sound good but noone does in reality, like backpedalling on a descent.

Assuming you put the old tyre inside your new tyre, they're doing to be about the same size so the old tyre's bead will poke out. There will be no gain in the old tyre seating on the rim, you need the outer new tyre to seat there otherwise it will move and flap.

Your mechanic says tyre liners cause punctures - thats because they have an end that abrades with motion. Your suggested inner tyre would have at least one wrinkle, because a 20" tyre won't fit inside a 20" tyre without some give. Or you could cut a sector out, leaving you with the same ends overlapping problem.

Instead of futzing around, buy tyres that have a decent puncture protection belt, like Schwalbe Marathons or any number of other brand/models that advertise an anti- puncture belt.

Since manufacturers tend to exaggerate, look at puncture ratings on https://www.bicyclerollingresistance.com/ They're all tested on the same rig for consistency.

Do also explore the option of tubeless+sealant, or tubes with sealant in them. They're not a perfect solution, but better than nothing.

Also learn to modify your riding - an ebike with 75mm tyres is not going to be light, so traversing any broken glass is just asking for punctures. Also learn to avoid bouncing over kerbs/curbs and through potholes. Any area of the roadside that has a "shoal" of gravel will harbour wires too. So avoid riding those areas. The roads are extra glassy on Saturday/Sunday mornings and Mondays too to an extent.


On the flip side, if you have spare used tyres, absolutely give it a go and report back here with your results. Try and avoid bias, in that new tyres are more puncture resistant than old ones, and replacing your worn tyres might be all that is causing a change in perceived rate of flats. Remember you can answer and accept your own question, that's allowed.

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    I don't disagree with your recommendation to get a puncture resistant tire, however, the OP did indicate that they're hard to find in his size. (Possibly a locale issue.) – FreeMan Feb 13 at 16:46
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    Why would you backpedal on descent? – Reinstate Monica -- notmaynard Feb 13 at 16:57
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    @VinceO'Sullivan some things do appear to be difficult to get at a reasonable price in some countries. They may be available, but adding shipping and customs issues, they become very unreasonably priced and/or exceedingly cumbersome to acquire. OP hasn't listed a location, so simply assuming that he could pop down to the local shop and/or hit up Amazon.co* to pick up any desired product may be a bit much - especially since he indicated so. – FreeMan Feb 13 at 20:01
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    I backpedal on descents, because it's fun. – HemiPoweredDrone Feb 13 at 20:52
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    In the cold I forward pedal on descents to keep my legs warm. Just marking time, so in a high gear with cadence to match my speed, but no real force, and alternating with a bit of stretching and fidgetting on longer rides (@ReinstateMonica--notmaynard) – Chris H Feb 14 at 8:44
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A Slightly different approach, Get an old tube, cut it open, then wrap it around your existing tube. put the whole lot inside your tire and fit as usual.

you can add more than 1 tube with no issue, I've done this in the past for unparalleled puncture resistance!

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  • Using an old tube to line the tyre is a similar trick, which gives you mire rubber at the tread, but doesn't protect the sidewalls. However rubber only really adds thickness unlike harder materials. – Chris H Feb 13 at 9:29
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    Yeah, but I'm curious how effective this is compared to a liner, especially considering the weight. I imagine the puncture resistance from 1mm of rubber is significantly inferior to that of a couple of mm of Kevlar, and I wouldn't be surprised if the rubber was heavier. – Nathan Cooper Feb 13 at 16:38
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I have used "Slime" which is another option. You put it inside the tube and it will seal any punctures including any existing ones. I was getting multiple punctures each week due to a mile long thorn bush that was cut along my route. I probably have lots of thorns in my tyre now but it's still inflated fine.

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    YMMV, but I never found slime did anything to stop punctures. All it did was coat the inside of my mudguard with green crud. – Graham Feb 13 at 14:06
  • +1 for slime. I've ran a fat ebike for hundreds of miles with just slime and I've literally pulled nails out of my tire and kept riding. The slime does a good job at holding. Just pump back up to proper PSI when I get a chance and keep riding like it never happened. It's only failed me a single time when I got a large puncture and couldn't fill the hole. – Travis Feb 13 at 18:29
  • All well and good until your valve gunks up and you end replacing the tube anyway – Dan K Feb 14 at 12:37
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    All good comments and yes it can be messy, gunk up your valve and I'm not sure of the life of it. The thing I like about it is that if you do actually get a puncture (from something that would go through a puncture proof layer) then it just self seals (hopefully). I suspect if you do get too large a puncture, that you could potentially seal it by rotating the hole in the tyre away from the hole in the inner tube. As I said, it's an option and I also use it on an e-bike. I would be more reluctant to use it on something lighter weight. – Oliver P Feb 14 at 15:59
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Sealants work best in a tubeless setup. I've had mixed results when used in tubes. Also note that many (all?) sealants have a limited shelf life. I use Orange Seal and they recommend replacing at 1 year (yes just one year). I work in a shop and regularly see bikes where the tire is flat and the sealant is clearly years old and does nothing but add weight.

My experience has been that sealant inside an inner tube does not dry quickly. My bikes that are setup tubeless need regular refreshing (usually 3 to 4 months). I had some 700x40mm (ish) tubes where the Orange Seal was still liquid after 2.5 years, and it didn't seal when I got a thorn. To make it worse, the sealant was still liquid so it made quite a mess.

On the positive side I've watched as Slime in a tube sealed more than a dozen holes when a friend rode over a goathead bush. So yes the sealants can work.

Aside from sealants I would suggest the tire liners. A sturdy e-bike tire will resist cuts and the liners should help reduce punctures. Note that as tires wear there's less rubber protecting the tube.

In cases where the sealant is partially sealing the puncture a CO2 inflation system is awesome as it allows one to quickly inject some air, ride a ways, and then inject some more. It's not an ideal setup but it can get one home. DAMHIK :-)

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you could consider using strips of Kevlar for puncture protection. It's also used in anti-stab vests (which protect the wearer from knife attacks and such), that being said you will need a few layers to get the desired protection. IIRC you need approx 28 layers to make it bulletproof (Uzi, 9mm etc.) :)

You could tape the layers together to keep them from separating, for example using duct tape.

You can get quite a lot of the raw material (woven Kevlar sheets) for cheap (from Aliexpress for example), here's an example: https://nl.aliexpress.com/item/32796301207.html?spm=a2g0o.productlist.0.0.10ff47eaX3gE6p&algo_pvid=b75e54fb-b62f-41a2-8a23-a1c941ce1a3b&algo_expid=b75e54fb-b62f-41a2-8a23-a1c941ce1a3b-17&btsid=0b0a050115816127744011594e0dc4&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_ there are many different options/sellers.

An alternative: https://nl.aliexpress.com/item/32628896034.html?spm=a2g0s.8937460.0.0.60da2e0ejHDAtt

As you can see in the description they tested it with an UZI Sub Machine Gun and it passed their test (at 24-28 layers thickness from what the seller has told me).

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    FWIW, don't try this at home. "Bullet-proof" is not the same as "stab-proof" and people have been killed showing off their fancy kevlar body-armor. If body-armor is truly made knife-proof it will usually contain a special layer (like a wire weave or ceramic scales) specifically to resist a knife. – DavidW Feb 13 at 18:04
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    @DavidW true, not all bulletproof vests are also 'stab proof', however many stab-proof vest also use kevlar (albeit in a tighter weave) to achieve the stab resistance. link: safeguardclothing.com/uk/articles/… I would indeed not recommend using your tire as a DIY bulletproof vest but other than that what reason would you have not to try it on a tire? I'm not suggesting people create their own body armour, I'm suggesting a way to protect a tire so i don't see why one shouldn't try it at home.. – Maarten -Monica for president Feb 13 at 19:06
  • @DavidW either way I'll try it on my own tires and see if the results are indeed positive. what could go wrong? – Maarten -Monica for president Feb 13 at 19:13
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    Spinskins was a kevlar tire liner for bicycle tires but alas they're no more. Lots of complaints on line about the liner actually causing flats in the tube – NoCo Rider Feb 13 at 23:27

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