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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 '16 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 '16 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 '16 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 '16 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 '16 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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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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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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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.

  • 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 at 3:00

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