I have a bike that has 27.5 tubes and after like 5 weeks the tire deflated fully. This also happened to my 26 inch tubes and they are brand new ones. The 27.5 and the 26 front tire deflated only. Not both or rear.

So I added air to them and they were back to normal.. any help to what caused this?

I've had this happen quickly when I leave my bike in sisters garage. Is it cold ? Or maybe drastic changes in temp? Tubes deflate naturally w time. I almost always pump mine up before every ride! If they are totally empty within few weeks though you could have a pin sized leak in tube.

Tires and tubes must be inflated every week or so. Most folks top off their tubes/tires before each ride, even if they ride several times a week.

It's normal for air to slowly leave tires... I always set my pressure before every ride. However, butyl inner tubes lose pressure very slowly once they're down to low pressures, and it shouldn't be going fully flat in a month. (Unless you're running latex tubes, which you likely aren't.)

Are you using Presta valves? If so, make sure that the valve cores are properly secured to the stem. Also, if the center pin is bent, that could possibly cause a slow leak.

I certainly don't pump up before every ride. I do regularly check the pressure (thumb test), but if it feels OK, I'll ride. Maybe I'll pump the tires once a month or so, or before a big ride (100+ miles, or a few hundred miles RT). It is also tire size dependent. My 20x4 1/4 tire can hold a lot of air.

As far as bleeding flat.

• If the tires become low (still some air inside) over a few weeks, it is probably normal air leakage due to disuse.
• If the tires become completely flat, beads unseated, no pressure, then it is often a sign of a slow leak (puncture or faulty valve?) unless the tire has been sitting for several months, or perhaps over a year.

I went over to my lbs and they said that either that my tubes are bad/puntured or that temp changes will change my tire pressures.

That is ALWAYS a POSSIBILITY.

But tubes do lose air THROUGH the material too. I don't think any of my bikes would retain a rideable pressure for several weeks. Thicker tubes, as big as can be fitted, wide tires will last longer.

Remember that only b/something is true doesn't guarantee that it is important.

1)Temperature changes does influence pressure, but doesn't change the amount of air in the tire. Once back to the same temperature as when last checked, the pressure will be the same again.
2) the pressure changes due to "normal" temperature swings are really, really small.

After my blowout a few weeks ago, I've thought about that some.

PV=nRT, with everything fixed except Pressure, and Temperature in Kelvin, then if your temperature changes by about 50°F, or about 25°C (K), then your pressure in the tire might change by about 10%. Not a huge change, but for a tire at 100 PSI, it could decrease to 90 PSI going from hot to cold, or increase to 110 PSI going from cold to hot.

So, probably not enough to flatten a tire, but perhaps in my case enough to take a tire from the maximum pressure to a few percent over max.

Last tour I went on with the fiancee, one of her tires needed topping off every morning. The other three tires (between the two of us) were fine for most of the week and a half without being touched. No puncture, all four tubes came from the same place, same brand, same model. Never been able to figure it out. I've got the same tubes in yet another bike, that I have to keep topped off fairly regularly.

I've just come to expect some individual tubes do a better job than others, with no real correlation to brand/model/price. I'd bet if you moved the tubes to the back on your bikes, you'd see the issue there, it is just coincidence that they both happened to be front.

Because they have a lot more rubber, in them, much thicker, so heavier..

Thorn resistant tubes will retain air longer, but butyl rubber still has some porosity, even thick like car tires.

top up the PSI for best riding ..

Did you inform them that you often go a month or longer without pumping the tires back up, or did you just say "hey, my tires keep going flat"?

Bike tires aren't like car tires, you need to top them off regularly. Even perfectly-good tubes lose air at different rates. Become friends with your tire pump.

Seems pretty normal to me. Even car tires need to be topped off every so often, just not to the same degree as bicycles. Some individual tubes are better/worse than others as well.

Here in Houston, in the summer, tires go from 85 to 60 psi in a week. As the pressure drops, the loss is less, but in five weeks it could be down to 0-20 psi (unusable). I inflate tires once or twice a week (a 110V air compressor for bike tires helps a lot..).

Yeah maybe I got bad tubes or I got a puncture in em'

4 tires do this?

Are you tightening the presta valve "thing". Not the plastic cap, but the metal piece that stops it from being pushed?

Nah.

Or rather, it shouldn't.

The valve, regardless of type, is meant to seal by itself. Caps are there to protect against dirt and grime entering the valve.

Accepting the theory that a valve cap might slow a valve leak, it still won't do anything for air seeping through the rubber.

5 weeks? I check and top off my tires before every ride! Re inflate your tires and see if they hold air. Check them every couple of days. If it goes completely flat after a couple of days, you have a puncture or defective tube. If it is down by, say, 10 or 20%, that is normal and you just need to top them off.

Natural air loss should be minimal, not something you need to make up daily or weekly. Variations with temperature should cancel out on average. and within one week you likely don't have 50°F swings for that to matter. And assuming all your bikes are in the same temperature, there must be something wrong with the tube/valve. Unless you for some reason take the wheel out and store it in the freezer ....

How did you check for leaks? I say that because I had a slow leak in my rear tire and couldn't tell by "listening" or "looking". It is just i filled it to 55 psi and at the end of a ride the next day i could feel it getting empty and measured at home 30 psi only. I filled the sink with water and the pressurized tube in and saw the tiny air bubbles. You have to do that slowly because the outside of the tube also retains some micro-bubbles of air at first. The valve also could be the problem. Most Presta valves don't have replaceable cores, so you may need to replace the tube.

Not true. In over 20 years, I have a sense of normal air loss vs. a puncture/defective tube/defective valve. Normal is down maybe 10 or 20% after sitting a week. A puncture you know right away. Completely flat, or down 80 or 90%.

I think I "normally" find tires lose air at different rates. Don't know why. In some cases, probably less than perfect patch job. As long as I can get through a ride then it's good.

scott s.
.

I can see latex tubes losing most of their air over 5 weeks. Butyl, not so much unless there's a hole or a leaking valve.