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I'm looking for a rule of thumb as to how much air loss over time is considered acceptable / normal for a hybrid tire.

Surprisingly I have not been able to find much on this upon Googling. In this post:

How long should a road tyre hold its pressure?

Two people with road bike tires in the 110-120 psi range stated they normally lost 5-10 psi per day. This seems high, especially if closer to the 10 psi figure.

In my particular case, I'm running 700x32mm tires and the sidewall states "Min 35 psi, Max 75 psi". I'm currently inflating every other day to about 75 psi (perhaps slightly higher, but always under 80 psi) and I find I'm loosing about 1-2 psi per day, which seems roughly normal but I'm really not sure.

I'm using Giant tubes I got from a Giant dealer so I'm confident I'm not using poor quality tubes, and the tires are Giant branded hybrid or "gravel grinders" that are relatively tough and in good shape so I'm confident I don't have a puncture or slow leak problem (wheels/tires/tubes all OEM/stock parts on a 2017 Giant AnyRoad CoMax).

How much is considered normal?

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    I would say that 5-10 PSI per day is about right, for a road tire at 100 PSI. I figure road tires need to be refilled about every three days. 75 PSI for a 32mm road tire is on the low side, but at such pressures I'd guess you'd still be losing 2-5 PSI per day. At such a low "normal" pressure you'd want to be even more diligent about filling the tires frequently.
    – Daniel R Hicks
    Nov 26, 2016 at 12:38
  • How much is considered normal is a perfectly reasonable question but this isn't the right place for collecting lists of people's experiences.
    – David Richerby
    Nov 26, 2016 at 13:44
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    I will add that I was on a multi-day ride about 20 years ago, and the first or second evening encountered a guy changing out the tubes in his bike and his wife's. He had some fancy new tubes that were supposed to roll better. Two days later I encountered him changing back to the old tubes, as the new ones leaked down in 12 hours. Some tubes ooze air much more rapidly than others.
    – Daniel R Hicks
    Nov 29, 2016 at 12:27
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    I find that after 2-3 weeks of 20 km/day its time to add some air. If you're pumping daily to get back to riding pressure, then you have a slow leak. Could try a new tube, or you could add some sealant assuming the valve core is removable.
    – Criggie ♦
    Dec 29, 2016 at 6:49
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    @Criggie - No way could I go two weeks without airing my tires. I generally run them about 100, and in two weeks they'd be down below 80. And this has always been the case, with multiple bikes, multiple tires, multiple tubes. (Generally around 35mm.)
    – Daniel R Hicks
    Dec 29, 2016 at 13:39

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Tyres will always lose pressure over time, I would say that for cycle tyres 1-2 psi is closer to the norm for most including me. This is mainly due to the microscopic pores in the tyre/tube which air molecules escape through over time.

However don't forget that the air in tyres also expands and contracts with temperature, so on colder days tyre pressures will decrease slightly, and vice-versa on warmer days pressures will increase, it is considered that roughly 1-2 psi with every 10 degree increase/decrease in temperature is the norm here.

Natural deflation also occurs more rapidly the higher the pressure so as you reach a tyres max pressure it will deflate quicker, and thus to keep your tyres at max pressure you'll need to inflate them every couple of days due to the higher pressure loss rate.

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The answer is already in your question. To quote, "they normally lost 5-10 psi per day". Since you are using lower pressure and thicker tubes, it can be expected that you would lose pressure slower, somewhere around 1-2 psi (which accidentally is the exact number you posted).

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Air permeates through rubber. The more pressure under which this air is trapped inside the tube, the faster it will escape. Air also escapes through the valve. Again higher pressure tubes will let out air faster through the valves. Of course there will be minor variation depending on the quality of the tube and valve. About 5/10 psi loss per day in a high pressure road tube with 100 psi air is normal. Being light weight, I keep 80 psi in the rear wheel and 60 psi in the front. My front wheel loses less air.

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I've experienced anywhere from 2-5 psi loss per day on my tubed (Continental tubes and tires) 700x23's and 2-20 psi per day on my 700x38's tubeless (using Stan's sealant, not their race-styled sealant). In the tubes I pump to 115 psi with the tubeless usually pumped to 60 psi.

The higher figure on the tubeless is when first placing a new tire with new tape. It takes time before the sealant works its way into all the micro-seals (is my guess).

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A loss of 5 psi per day seems very high to me. I've tested this on my bike. With Continental Gatorskins, 700x28, and Kenda tubes, I consistently lose 1-2 psi per day. Also, since tire treads are permeable, it may have more to do with the type of tube than the type of tire that you are using.

Also, each time you disconnect your pump, there is a loss of air. And each time you attach your pump, there is a loss of air as the tire pressurizes the pump's hose. So if you pump up your tire every day, even if your tire hasn't lost any air, you will see a lower pressure. Try this: pump up your tire to 100 psi. Then disconnect and reconnect your pump and check the pressure again.

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  • You don't say what pressure you run. You'll lose more, in PSI, if your tires are nominally 100 psi vs 60.
    – Daniel R Hicks
    Feb 8, 2019 at 3:00
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Continental tire ( they make tubes as well ) states that their tubes loose about 5 psi per week and suggests topping them off on a weekly basis.

This information is not published but they will tell you as much on their support line if you speak German.

For a tube and tire combination, the tube is designed to hold the air in, not the tire and is the point of loss to consider.

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700x32mm tires really sound more like road tires than hybrid bike tires.

My bike has 700x28mm tires, and they lose pressure from 7 bar to 5 bar in two weeks. That's 2.4% per day.

The pressure loss rate as a percentage seems to reduce somewhat as the pressure becomes lower, so I suspect 700x32mm would have somewhat lower pressure loss rate due to lower pressure, maybe below 2% per day.

1-2 psi is about what I'd expect. Note that many pumps have a "dead space" that sucks some air every time you measure the pressure. Thus, if you have a tire at 75 psi, and measure the pressure thousand times in the same day, I suspect it will no longer be at 75 psi. So the true pressure loss rate could be lower.

Don't worry so much. Bike tires are designed so that you can lose 30% pressure and still use them.

About the only thing you can affect is if the tube has removable valve core, how tightly it's screwed in. I once had a tube straight from the factory that lost air suspiciously quickly. Tightening that valve core solved the issue.

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    "Hybrid" covers a wide range from not quite MTB to almost a flat bar road bike. My trekking style hybrid (which would have served as a flat bar tourer) came with 35s but I ran 28s on it most of the time
    – Chris H
    Dec 17, 2022 at 18:33
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    You can lose 30% of your pressure only if 70% of your inflation pressure is more than the minimum pressure you can run for your equipment + terrain + riding style. For instance, I run about 19 psi and 22 psi (front rear on my mountain bike). Loosing 6 psi in front means the tire rolls in hard corners and I'll dent the rear in chunky sections.
    – Paul H
    Dec 19, 2022 at 15:00

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