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I recently picked up a pair of Schwalbe Aerothan inner tubes which are made of plastic and very lightweight. The manual for these tubes indicates that the user should not inflate past 4.5 PSI. Quote:

ASSEMBLY INSTRUCTIONS AND INSTRUCTIONS FOR USE

[...]

Always use a suitable rim tape.

Inflate Aerothan Tube before assembly. Max. 0.3 bar/4.5 PSI. Inflating to a high air pressure when not mounted may cause deformation and damage to the tube.

Note: Aerothan Tube should not wrinkle.

My question is, how can this be possible? Surely I need to be able to pump the inner tube at least up to the tire recommended pressure, which is 90-120 PSI.

Am I missing something important here? I understand from other posts like Does the inner tube affect the maximum PSI? that inner tube pressure should not matter, but surely if the manufacturer warns not to go above 4.5 PSI, there must be something I am missing?

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  • 4.5 bar = 65 psi. Could you post a photo of the manual in question?
    – Paul H
    Oct 26 '20 at 17:58
  • Sure, just added the picture.
    – Omar N
    Oct 26 '20 at 18:07
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    yup -- that's the max pressure without a tire (inflate...before assembly)
    – Paul H
    Oct 26 '20 at 18:09
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    The manual page you showed clearly answers your question. It says you must inflate the tube before inserting it into the tire and the maximum pressure for this initial inflation is 4.5 psi. "Inflate Tube before assembly. Max 4.5psi. Inflating to a high pressure when not mounted may cause deformation and damage to the tube."
    – Gary E
    Oct 26 '20 at 23:10
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    Please DO NOT POST TEXT IMAGES (ONLY) - non-sighted readers, search engines, users on mobile etc. will have trouble reading this. Please type in at least the relevant part. I took the liberty of doing it for you in this case.
    – sleske
    Oct 27 '20 at 12:19
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Most likely this low number refers to inflating the tubes without the tire, as a balloon.

When installed inside a tire, the majority of air pressure is held by the tire casing, not by the tube.

A similar warning about not inflating outside of/without a tire came with my Tubolito inner tubes, but the wording was more clear in my case.

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  • 25
    For me it is as explicit as it gets. before assembly and when not mounted
    – Vladimir F
    Oct 26 '20 at 18:14
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    To be as fair as possible to the OP, the delivery in terse disjointed sentences doesn't help. The two sentences could be imagined to be essentially separate instructions. And dismounted? Most people think of an inner tube as being "fitted" not "mounted". The rider is mounted or not, which is a whole extra level of possible confustication! :-D What's wrong with "before fitting this tube into the bicycle tyre, very lightly inflate it (to no more than 4.5 PSI)." Oct 27 '20 at 8:03
  • @GrimmTheOpiner someone decided to use legalese instead of normal language here, with usual results. Note one more statement there: "Reassemble Aerotan tube only with the same tire size". A person has not even fitted them for the first time, and they are already being warned against the second fitting! What it essentially means is that, once inflated to full pressure, these tubes stretch permanently to a fixed diameter. Fitting them into narrower tires afterwards will create wrinkles; Now one needs to note a warning against wrinkles a couple of lines earlier. Oct 27 '20 at 8:22
  • Many people, @GrimmTheOpiner, think of an inner tube as being "installed" not "fitted". 'cause many people live in the US, not the UK. ;)
    – FreeMan
    Oct 27 '20 at 11:48
  • @FreeMan ...but not mounted! : ) Oct 27 '20 at 13:34
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It is common to inflate a tube just a little bit before you install it in the tyre. This gives it some shape and helps prevent it getting twisted or pinched, with a little care from the user.

This is the stage described in the manual you've shown. With a standard butyl tube you can inflate those much more than needed with no ill effect, the rubber just expands like a balloon, however you have fancy ones which would be damaged by doing that.

This 4.5 psi is the manufacturer's limit for these special Aerothan tubes before going in the tyre, stretching them beyond the resulting size would damage them. Once they're in the tyre and it is fitted you can inflate up to the required pressure for riding.

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