Bicycle Mechanics - How often should the tires need more air?

After I pumped my tires full, and didn't even use the (new) bike for 1-2 weeks, one of the tire was not as hard to the touch any more. It's still quite full of air, but it bounces a little when squeezed, unlike the hard solid feel soon after pumping. As I said the bike was sitting inside for the week after pumping. The other wheel was better. What's normal?

I pump up before each ride or each day which ever is longer.

Road bike tires need to be pumped up before each ride.

How often should the tires need more air?



It depends on how many holes they have in them!:lol:

Seriously though, this air loss is normal. If you want optimal tire performance, even from a 40 psi tire, you have to fill up every day or ride which ever is longer. If you are using really high pressure tires, 100psi or more, you can expect some air to disappear everyday.

Rubber is actually porous and lets the air though. A great example you can see of this happening a lot faster is a balloon. I think for people with money to burn, in exotic cars, they fill the tires with nitrogen or C02. The molecules are larger and don't go through the rubber as fast allowing for less top offs, but you have to buy the stuff as opposed to pumping free air.

My bike is brand new, though, only ridden 2-3 long distance, and total 5-6 times (some just nearby errands). The reason I didn't think it very normal is that the front wheel is very good, hardly lost any air, but the rear wheel has obvious loss. It's a 700 wheel. Probably the rear wheel came with more holes :mad:

The tires don't care if you ride them or not. The air leaks out at the same speed either way. Bigger mountain bike tires hold more air at less pressure so the pressure doesn't go down as fast as with skinny road tires. I find I need to pump my road tires up about once every 3 to 4 days for casual riding. The skinny mountain bike 1.25 tires about once a week. Big fat tires urban jump, cruiser or off road tires would be about the same once a week to maybe every 10 days. So it's very reasonable to expect your tires to be that low after that much time.

Rear tires get more flats, wear out faster as they have more weight on them compared to the front tire.

My front tires get more holes, from picking up thorns. :mad: The front ones blaze the trail. Every form of fauna here has thorns. If I see a stick or leaf in the road I avoid it. Off road I just cross my fingers.

Someone has to say it: As often as needed.

I pump mine once or twice a week.

Rear tires get more flats, wear out faster as they have more weight on them compared to the front tire.

Different in my case, though. The day I bought the bike, I took it by subway without riding, and I could already feel the difference between the two wheels. Maybe they didn't pump enough the first time, but the next time after both pumped, it's still the rear wheel that lost more air, so I think it's the wheel quality in this particular case.

Not the wheel but perhaps the tube has a slight weep through the valve or there's a very small pinhole manufacturing defect in the tube.

Not the wheel but perhaps the tube has a slight weep through the valve or there's a very small pinhole manufacturing defect in the tube.

If that's the case, can't ask the manufacturer to replace it?

If that's the case, can't ask the manufacturer to replace it?

Replace the tube, its a $4 item. If you just got the bike then take it back to the shop maybe they installed it wrong or had a bad tube.

If that's the case, can't ask the manufacturer to replace it?

Not a defect, but if your bike shop likes to service whiners, go for it. Your next tube could have the same leakage rate...or not. If you have a schrader valve check to see if its core is tight; it just may be as bcrider says about a small leak otherwise. It's not a big deal and doesn't mean anything's defective. 1-2 weeks on my road bike I know I'm pumping up to my preferred pressure, mountain bike maybe not.

PS Get a gauge and be specific...

That slow a leak would not be seen as a defect. In fact I'm sorry I called it that. Tubes are made quickly for cheap. It stands to reason that some will be a shade better than the others and some a shade worse. If it leaked down to flat in a week then you'd have a case for asking for a new tube. But what you are seeing is perfectly acceptable and totally ordinary. If it's a schreader valves try venting some air out and then pump back up. Or even remove the core, blow it out and replace it. If there was a bit of grunge in the core seat this MAY slow down the weeping. Or not....

Learn how to patch a tube.

So do I, both my road bike and Mountain bike. Even when they feel find, I always find out I am at least twenty pounds low.

Many thanks, everyone! Yes comparing to some of your bikes, it seems not so bad. (Actually, if both wheels lost equal air, I wouldn't have been worrying :D)

mine generally needs 10 to 15 lbs each time before i ride. tire still feel hard but i always check

PS Get a gauge and be specific...

Agreed. If you don't use a gauge, you're just making wild guesses about the pressure in your tires.

If it really bugs you take it apart and fill up the sink and do a real leak test. If it's a cheap bike or a bike from a store that does high sales volume check the rim strips. An off center rim strip will cost you a tube real quick. My chinese cruiser had this problem. It had a hole in the tube three days after I aired them up for the first time.

Yes as other have mentioned daily if you want to keep it at a constant pressure. My weekend road bike gets pumped up before every ride.
My commuting bike I tend to do it once a week but pressure does drop as much as 15 psi in that time.

One time I got exceptionally lazy and I didn't fill my tires for over a month, and I ride 3+ times a week over south bay area roads. They were down 25 psi when I finally dragged out the pump and checked. No flats either. For some reason these tubes are awesome, and it takes near a month before I start noticing any difference in the quality of the ride/whine of the tires against the road at speed.

However, if you like to run a little low to gain some more plushness in your ride, you should check far more often than I do. I like my tires at 110 or so psi, both, and I weigh 160 lbs. I run a little higher by preference.

Buy a tire gage, for bike tires, and learn what the proper inflation pressure should be, and keep it there..

Buy a tire gage, for bike tires, and learn what the proper inflation pressure should be, and keep it there..

That's what I'm thinking after reading the replies here. How to know the proper pressure of my bike? Is it by feel or it's specified by the wheel maker? (sorry if this sounds stupid question)

Here use this and adjust pressure to personal liking tire size and rider weight dictate an average tire pressure starting point.
http://www.michelinbicycletire.com/michelinbicycle/index.cfm?event=airpressure.view

That's what I'm thinking after reading the replies here. How to know the proper pressure of my bike? Is it by feel or it's specified by the wheel maker? (sorry if this sounds stupid question)The maximum pressure will be printed somewhere on the side of the tire - you may have to look closely. Depending on your weight, you want to be at your max pressure or somewhere below (according to the Michelin chart linked by JTGraphics)

..I think for people with money to burn, in exotic cars, they fill the tires with nitrogen or C02. The molecules are larger and don't go through the rubber as fast allowing for less top offs, but you have to buy the stuff as opposed to pumping free air.

From my experience with bike CO2 inflators, CO2 leaks faster than air.

BTW, air is 75% nitrogen.

It depends on how many holes they have in them!:lol:

Seriously though, this air loss is normal. If you want optimal tire performance, even from a 40 psi tire, you have to fill up every day or ride which ever is longer. If you are using really high pressure tires, 100psi or more, you can expect some air to disappear everyday.

Rubber is actually porous and lets the air though. A great example you can see of this happening a lot faster is a balloon. I think for people with money to burn, in exotic cars, they fill the tires with nitrogen or C02. The molecules are larger and don't go through the rubber as fast allowing for less top offs, but you have to buy the stuff as opposed to pumping free air.

Nitrogen. CO2 is a smaller molecule than N2, so CO2 passes through a rubber membrane faster then N2. However, it's a pretty negligible difference, since so much of plain old air is just under 80% N2 anyway.

Molecule size does play into permeability but concentration gradient is far more important. When you have a high pressure tube filled with pure CO2 vs an atmosphere that is 0.03% CO2 at a tiny fraction of the pressure, it causes CO2 to rapidly exit the membrane.

Car people do NOT fill with CO2 because it leaks out extremely fast (5 times faster than normal air) and that would lead to rapid tire-pressure related sidewall failures (Remember the FordExplorer/Firestone debacle and how we all have TPMS sensors now?).

Car people use pure N2 because, thanks to the process of generating 'pure' N2, it is free of atmospheric moisture. Atmospheric moisture is what causes the greatest pressure changes in response to heat so a tire filled with N2 vs Air (which is mostly N2, O2, and other gases including gaseous H2O) will be far more stable in pressure and therefore have more predictable handling dynamics. At least, that's why F1 engineers use it. street car owners use it because the tire shop tells them "it's better" or because they are posers.

....greatest pressure changes in response to heat so a tire filled with N2 vs Air (which is mostly N2, O2, and other gases including gaseous H2O) will be far more stable ...

+1 .... it was the high heat of racing/motorsports applications. Also used in pressurized racing shocks for the same reason. I am ignorant of any other benefit.

+1 .... it was the high heat of racing/motorsports applications. Also used in pressurized racing shocks for the same reason. I am ignorant of any other benefit.I imagine the lack of oxygen would be beneficial inside any kind of precision mechanism to prevent oxidation... but yeah, predictability is key.

That's what I'm thinking after reading the replies here. How to know the proper pressure of my bike? Is it by feel or it's specified by the wheel maker? (sorry if this sounds stupid question)

The maximum recommended pressure is shown on the side of the tire. That's what I put in my rear tire and about 5 pounds less in the front. The rear carries more of the weight. The ideal pressure should account for total load on the bike, more weight, more pressure.

Car people use pure N2 because, thanks to the process of generating 'pure' N2, it is free of atmospheric moisture. Atmospheric moisture is what causes the greatest pressure changes in response to heat so a tire filled with N2 vs Air (which is mostly N2, O2, and other gases including gaseous H2O) will be far more stable in pressureN2, O2, CO2 and H2O all pretty closely obey the ideal gas law at the pressures and temperatures found in our tires -- they're all pretty much equally stable in pressure.

HOWEVER, H2O will do one thing that the other gasses don't -- it can condense into liquid water at "normal" temperatures -- and that causes a massive difference in the pressure. So that is to be avoided at all costs, and while small percentages of water vapor aren't really likely to do that unless it gets really cold, it's pretty easy to make sure it's not an issue, by using almost perfectly dry N2 (or almost perfectly dry N2/O2, but whatever works.)

Narrow tires need higher pressure than wide tires. Narrow tires also hold less volume. So there are two factors which speed up pressure loss in wide tires.

Here is a chart off the top of my head.

tire width -- inflation interval

1.75" --------- 7 - 21 days
32mm -------- 1 - 2x week
28mm -------- 2 - 3x week
25mm -------- every ride

It depends on how many holes they have in them!:lol:

You had me laughing out loud with this one.

N2, O2, CO2 and H2O all pretty closely obey the ideal gas law at the pressures and temperatures found in our tires -- they're all pretty much equally stable in pressure.For bicycles, I agree it's mostly pointless to use anything other than air (when available) or CO2 (for on-road repairs). For a racing car tire which routinely sees very high temperatures (especially in racing applications, DOT-R spec tires operate in the 180-200deg range and higher end applications like Indy/F1/etc may operate much higher), the ideal gas law is out the window. They aren't even close. The difference over the operating temperature range can be several PSI different which, in an extreme-narrow-margin sport like F1, is the difference between podium and gravel pit. It's a hell of a lot easier/cheaper for a team to use dry nitrogen than risk unexpected handling or worse, an expensive crash.

But yes, for bicycles, it's pointless.

That's what I'm thinking after reading the replies here. How to know the proper pressure of my bike? Is it by feel or it's specified by the wheel maker? (sorry if this sounds stupid question)

For me proper presser is 90-100 psi on my road bike. I am normally 5-10 lbs below manufacturer maximum pressure. I judge pressure by feel when on the road, but I always fill up before the first ride of the day.

Get a floor pump and pump it up before the first ride of the day and you wouldn't be worrying about this. If the tire is flat before the end of a day, you have a problem and need to replace the tube and find the problem.

See this article by Jan Heine (http://www.vintagebicyclepress.com/images/TireDrop.pdf), based on research by Frank Berto, for recommendations on the best pressure at which to run your tires.

Rear tires get more flats, wear out faster as they have more weight on them compared to the front tire.

While that is true, it has no bearing on the rate at which air diffuses out of tubes.


My bike is brand new, though, only ridden 2-3 long distance, and total 5-6 times (some just nearby errands). The reason I didn't think it very normal is that the front wheel is very good, hardly lost any air, but the rear wheel has obvious loss. It's a 700 wheel. Probably the rear wheel came with more holes :mad:

The tubes in your bike are not identical. No two tubes are. Diffusion of air out of the tube depends on many factors including pore size. I wouldn't find the difference you observe to be much of an issue. You may want to do a dunk test (dunk the tube in water and look for bubbles after pumping it up to about double size) but I doubt that you'll see anything.


Nitrogen. CO2 is a smaller molecule than N2, so CO2 passes through a rubber membrane faster then N2. However, it's a pretty negligible difference, since so much of plain old air is just under 80% N2 anyway.

Nope. For all measures, CO2 is a huge molecule. The C-O bond length is around 120 pm (picometers). There's 2 of those, plus the atomic radius of 2 oxygens. The bond length of nitogen is 78 pm plus the atomic radius of the N atom. Pretty small.

CO2 diffuses out of the rubber by dissolving through it.

Thanks a ton for the rich information! I'll check what's printed on my tires when I get home (it's 700x35c). Now I'd like to know, what's wrong with pumping by feel, to stop pumping just when the tire feels hard and is not bouncing any more? Just do not continue pumping. Is that not OK?

See this article by Jan Heine (http://www.vintagebicyclepress.com/images/TireDrop.pdf), based on research by Frank Berto, for recommendations on the best pressure at which to run your tires.

I like that article for its approach. It seems to recommend lower pressures than I would expect. Has anyone experimented? I weigh about 175 lbs (80 kg) and I pump my rear to about 105 and my front to about 95. This is with 25 to 32 mm tires.

The reason gauging your pressure by feel is that it's inaccurate. When you get a gauge, you'll see how miscalibrated your fingers are.

Thanks a ton for the rich information! I'll check what's printed on my tires when I get home (it's 700x35c). Now I'd like to know, what's wrong with pumping by feel, to stop pumping just when the tire feels hard and is not bouncing any more? Just do not continue pumping. Is that not OK?If you've got a flat on the road, pumping it up by feel is usually just fine. Most portable pumps suck anyways (some suck less than most, but still suck compared to a full sized one (http://www.amazon.com/Topeak-Road-Morph-Bike-Gauge/dp/B000FI6YOS)) and so you may not want to go up to the full 120 psi or whatever anyways.

At home, you should just get a pump with a built in gauge.

(edit: oops this page 2 covers it, but to repeat...)

the pressure range should be stamped on your tires.. you have to look pretty hard sometimes...

I have 1.25" MTB tires and have slime in the tubes and have only needed added air once in
more than 2 months now after getting the pressure right the first time...
and im not sure that one of them really even needed it.
(i have a air tank and just pop some in there then check the pressure if they are feeling a little yielding )

even brand new tubes may leak a bit at different rates...
if the tad bit of weight is not a concern, slime will help...
although i hear it is a nightmare if you get a real gash in the tire/tube.

Now I'd like to know, what's wrong with pumping by feel, to stop pumping just when the tire feels hard and is not bouncing any more? Just do not continue pumping. Is that not OK?

Most experienced people use a pressure gauge in leu of the thumb method. The thumb method is fine when doing a field repair but when you return home a floor pump and gauge is best. Does your thumb know the difference between 65, 90, 100 or 200 psi? How hard is hard?

after a few snake bit flats, you will figure out that the thumb isn't too accurate.

Thanks a ton for the rich information! I'll check what's printed on my tires when I get home (it's 700x35c). Now I'd like to know, what's wrong with pumping by feel, to stop pumping just when the tire feels hard and is not bouncing any more? Just do not continue pumping. Is that not OK?

Try first finding out what pressure suits your needs best (it's a combination of the specific tires you use, your weight and riding environment). Then maybe you can see if you can educate your fingers accordingly (not too likely if you like the higher end of the pressure range for that size tire). For my road bikes my fingers aren't that smart and rely on a gauge, but in the range I use for my mountain bikes, I rarely pull out the gauge.

I like that article for its approach. It seems to recommend lower pressures than I would expect. Has anyone experimented? I weigh about 175 lbs (80 kg) and I pump my rear to about 105 and my front to about 95. This is with 25 to 32 mm tires.

The reason gauging your pressure by feel is that it's inaccurate. When you get a gauge, you'll see how miscalibrated your fingers are.

I've pumped up according to the chart but I weigh 240 so the challenge is finding a 700x 23 or 25 tire that is rated high enough for me to get it where it recommends me to be. FWIW, I don't own a freestanding pump, just my mini pump. I usually go my bike shop to use their pump because I know i'm not gonna run up and down 5 flights if I owned a pump. the morning of the nyc century i was hoping they would have a good pump at the starting line but they had nothing so I just winged it running a rear that I knew was too soft. When I got to the rest stop in prosepect park I topped it off, it was all the way down at 80psi!!!! I pumped it up to 120 and went on my way. The ride was SO harsh after that but definately snappier. There is a huge difference in comfort at lower pressures and the artice really talks about finding that happy plce for max speed yet to be comfortable, I think it does a fairly good job of that.

OK I just had a good look at my wheel (never knew there was so much info printed on it had I not read your replies--thanks). It says Min 50, Max 85 psi. Wheel is 700x35c. I'm not heavy, less than 130 lbs even when I just ate a big meal. The Michelin chart linked by JTGraphics does not show 700x35c, but it seems it should be on the leftmost side. Maybe 55 psi or so would be my case... Thanks again. I'm glad this turned out to be a very informative and educative thread :D

I usually opt for the high end of the pressurerange, the logic being that well inflated tires are accepted as being less prone to flats.

I usually opt for the high end of the pressurerange, the logic being that well inflated tires are accepted as being less prone to flats.

A properly inflated tire is less prone to pinch flats but I doubt that a tire with higher pressure is any more or less prone to flats in general. A few psi of air will make little difference to a sharp object.