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Tube gives different pressure advice than the tire. Which is correct? (⚠ innertube fits a range of sizes) (lemmy.dbzer0.com)
submitted 3 weeks ago by to c/bike_repair_tips@sopuli.xyz
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Normally tubes do not give a pressure spec, just a size. Tires always give a max pressure figure. Exceptionally, I bought a universal innertube for a range of sizes: 26—27.5″ (only because it was quite cheap). The box for the tube has a chart listing all the sizes and widths it can support, and a pressure for each size. for 26×1.75″, it gives a pressure of 3—3.5 bar. My tire gives a pressure of 4.5 bar. The chart on the innertube box indicates 4.5 bar only for the largest smallest size (26×1.50). As the air volume increases, the pressure is lower.

e.g.

|--------+-----------+---------|
| 40-559 | 26×1.50   | 3.5—4.5 |
| 47-559 | 26×1.75   | 3—3.5   | ←
| 50-559 | 26×1.90   | 3—3.5   |
|      … | …         | …       |
| 57-584 | 27.5×2.25 | 2.5—3   |
|--------+-----------+---------|

So this is annoyingly confusing. I pumped to 3.5 bar because I’m afraid to exceed the limit spec’d for the tube. Is that the right move?

all 7 comments

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[–] 4 points 3 weeks ago (1 child)

I kinda feel that most pressure is about what something can handle so you would want to go with the lower of the two. I would go more with someone who knows though than my theorizing.

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    • [–] 2 points 3 weeks ago

    I don't know the answer, but 3.5 bar matches the pressure I put into tires that size. My motivation is to try to get low rolling resistance, not because of a spec limit. I'm told higher pressures reduce energy efficiency in addition to transmitting more road vibration. (Or maybe because they transmit more road vibration?) I use online tire pressure calculators to get a recommended pressure.

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    [–] 1 point 3 weeks ago (2 children)

    Is the pressure on the tube a suggestion or a limit?

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  • [–] [S] 3 points 3 weeks ago (1 child)

    It’s “Luftdruck-Richtewerte”. Which is sometimes translated as guideline, or recommended pressure.

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  • [–] 2 points 3 weeks ago

    Recommended sounds like a guideline to me, but im not a bike mechanic. The tire/rim does almost all of the pressure containment, with the exception of the valve, but the valve should be capable of much more than 3.5 bar.

    I think you'll be okay at 4.5 bar. Some road tires are run at 6+, so 4.5 doesnt seem outrageously high.

    I'm not a mechanic though, just some idiot on the internet :)

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    • [–] 1 point 1 week ago

    I have never even thought about pressure rates of the inner tubes.

    I just check what is on the tyre and keep the pressure between those values. During winter on the lower end of the spectrum and during summer on the higher end.

    I usually use schwalbe inner tubes but occasionally other brands too.

    Never had any problems. Been frequently cycling for / commuting with bike for forever.

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