I bought a new bike about 6 weeks ago, I only recently needed to pump up the tyres.

I pumped up the front because it was low and while I was there I topped up the rear. I rode to work then at the end of the day the front is flat. I bought a new tube and installed it, pumped up both tyres again. Next morning the rear tyre is flat... Again after a pump it would last the day before needing to be pumped up again.

Same issue with both after topping them up. Why? I don't get what caused it. The tubes are Presta Valve Schwalbe Extra Light (406). What could I be doing to them while pumping to cause the slow (maybe 2-4psi per hour) leak?

That's not a slow leak. Slow is 0.5psi/day.

Check your rim, and the inside the tire for sharp protrusions.

When you changed your flat tube, there was a sharp object that punched the tube. You have to carefully check the tire inside looking for that object.

But it seems that you need a tire with a kevlar belt offering better puncture protection. Also, you can use a sealant.

I carefully checked the inside of the tyre for objects or sharp points, found nothing. Also I cant find any hole or even a mark on the tube I replaced. Plus the tyres are Duranos, they do have puncher protection and its strange they both had the same issue, both right after a top up.

Oh and I didn't change the tube till the leak already happened so there was no puncturing of the tube during installation. And the second leak was the other wheel of which I haven't touched ever.

It's really strange because today the rear tyre that deflated overnight held its air while at work today and the tube I took out of the front has no obvious leaks when I pump it up outside of the tyre. Also the valve position was the first thing I checked when both tyres deflated, the screw was down and sealed. It's a mystery to me. I would assume someone is messing with me but I live alone and my bike is locked in my house overnight... Meh, I'll just replace everything.

We can't tell you how you're getting punctures until you figure out where the tube's getting punctured. Is it along the outside of the tube, facing the tire? If so, there may be a sharp object that's worked its way into the tire. (Small wire shards from steel-belted car tires are a common culprit.) Is the hole along the inside of the tube, facing the rim? Maybe there's a problem with your rim tape or there's a burr on the rim. Is it at the valve stem?

Seems like it might be time for the ol' water test. Remove the tube, inflate it so it's about double its normal size, then submerge it in water. Wherever air is escaping, you'll see bubbles. The faster the leak, the faster it'll be bubbling.

As an aid to help find the source of punctures, many of us install our tires such that the maker's logo on the sidewall is lined up with the valve stem. When we get a flat and find the hole in the tube, we know how the tire and tube were situated relative to one another, so we can easily find the hole in the tire without having to check its entire circumference.

Dunk it, patch the hole (my guess is pinch flat) and air them up more often.

Depends on the tire size. My road bike 25c tires drop about 20-25 PSI per week. I inflate the rear to 105, and a week later it will be around 80. That's normal for tires that size. Other tires like 26x1.5 I've had slow leaks of 20-30 PSI drop after a week or two, which is not normal.

For me it seems like I have to do the water test quite often as I just can't seem to find the leak with my eyes or even ears. I patched a 25c tube the other day, but apparently didn't get it patched well enough. It was losing about 40-50 PSI per day. I did the water test and initially found nothing. Then I dunked it again at the new patch, and found one tiny bubble escaping about every second, to give an idea how slow the leak was. Normal punctures will show many bubbles escaping all at once. So I had to redo that patch, and all is good now.

Pump up the leaky tubes and try to check where the leak is. Maybe put them in water in the sink if you're at home to see if any bubbles appear. Check the valve hole and make sure that there is no rough edge on it. Check the rim tape and replace if it even looks close to being worn. They're only a few bucks so never hurts to replace it. I last bought a plastic rim tape that stretches over the rim and goes on securely. Was only around $4 or $5 at an LBS if I recall. Finally, check the tires. If you see any cuts, then take out the air pressure and pinch the cut to get a better look at it. I sometimes get 1mm or smaller slivers of glass and rock caught in the tire. Just got a front flat from that last Friday. Glad I checked and removed the sliver from the tire...

A few comments- If you're commuting using X lite tubes is not the way to get best reliability. I suggest you use standard thickness tubes. They cost less, are less likely to bleed down just sitting and withstand the slight ****** (stupid auto censor, let's try "pokes") and abrasions better then thin was ones. Running tires with penetration protection negates the more supple ride quality of the thin wall tubes anyways. Second is that a fine piece of wire, which will produce exactly the nature of a slow (and I do call a many hour leak down a slow one) leak you describe. But a fine piece of wire is hard to see, find in the tire casing and feel if you only run your fingers one way along the casing's inside. Additionally if the wire is the same length as the tire casing is thick it will only get pushed against the tube with pressure, as in when riding, and might not extend into casing's inside when no outside pressure is present. Lastly a barrier protection made of a woven fabric (as in Kevlar) is not much goos against wire as the wire will act like a sewing needle and poke past the fabric threads. A piece of glass/shard of flint will typically catch on a number of threads so will be stopped much more effectively. Last comment is how the fresh tube is inflated. If done with a CO2 device, as road side fixes are increasingly done with, there will be far quicker bleed down due to the CO2's greater ability to sweat through the tube, compared to atmospheric gases. If an ultra lite tube is used and a CO2 is used no surprise that a work shift will see significant pressure loss. I tell my customers to deflate the tire and reinflate with a pump (or compressor) twice if they did a CO2 inflation. This purges out the CO2 well enough to not have rapid bleed down. Andy.

Make sure the rim tape is covering all the spoke nipples.

When you replace a tube make sure it is set in the tire (not pinched) prior to inflating.

Some leaks are really slowwwwww. Had a bad valve that was leaking, underwater it was releasing a bubble about once a minute, took me a while to figure that one out.

Good luck.

Those Schwalbe tubes have a removable valve core. Check to see if they are tight enough.

I fondly remember my dad showing me how to do this when I was just a wee lad.

Buy super thick torn resistant inner tubes, next.

One time, I had a slow leak that I could never figure out. Sometimes it would hold pressure for a week, other times lose air overnight. I did the water test (no bubbles) and wiped the inside of the tire with a tissue to see if anything grabbed it and torn the tissue, again nothing. The rim tape was also good.

In the end, I just bought a new tube and that solved my problem. All that fuss over a $7 tube.... no more!

I would suggest turning the tire inside-out (this will help to open any small holes where a wire or such may be hiding) and running a cotton ball or microfiber cloth all over the inner surface to see if it will catch on the sharp object.

it's more complicated than that, and it involves the pressures. But never mind, the OP was talking about about a 406 wheel/tire, and so was I, since my core, anchor bike is a 406er.

...I once managed to find a source of repeat leaks in a series of new tubes for a poor woman who was near the end of her rope. It was a relatively new bicycle (like the one described) and it turned out there were some aluminum shavings that had dropped out of one of the spoke holes (created doubtless by the original drilling).

There were three or four of them stuck underneath the rim strip, and only managed to gradually penetrate it and punch a very small hole in the interior surface of the tube where it met the rim strip. Each one had sharp ends, and the only indicator for where to look for them was in paying attention to how the tube had been installed in the rim, where they were located with respect to the valve hole, and that they were on the inner wall surface (facing the hub, not the tyre).

I think that was my most successful save, cause she was ready to toss the whole wheel.

Those Michelin wire things (as stated already) are tricky to find because they often stay buried in the tyre unless it's under pressure. Another good reason for paying attention to orientation when you take the tyre, tube, and wheel apart.

Had the same thing but after checking here I marked the rim and tire with tape. Removed the tube and marked it too. Did the water test. Matched the tube with the tire and started checking the inside of the tire with my finger. Found a sharp point that I couldn't pull out so checked the outside and found a staple. After removing the staple everything has been fine.

I've also had the evil staple through the tire flat. I got it one rainy day going up St Nocholas Ave past Harlem School of Arts. A nice guy that saw me with the front flat told me about a small LBS on Amsterdam near 150th St. That little shop saved me that day. Crazy to think that you could actually get a staple into a tire. But apparently doable...

I recently got a flat in my utility bike's 26x1.5 hybrid tires, and found a small nail ~1.5" long that was stuck STRAIGHT into the tire, tube, and nearly punctured the inner rim-side of the tube. I don't see how that can happen, because a nail like that would never stand straight up on a rough asphalt road surface. It should have been laying flat on the road.

If the tubes use presta valves with removable cores, find a suitable tool and tighten the cores into the valve stems.
I have the experience that even a very high-quality (Schwalbe) tubes often come with slightly loose cores.

VC-1 Valve Core Tool | Park Tool
This tool would do, but there are many others, and you could improvise a bit.

once had a tire deflate abruptly 3 miles from home (but not all the way). took it out & it was still full & holding it's shape with air. replaced the tube & rode home. chucked the suspicious tube. freakin' gremlins

I have these Panasonic "Uff Dah" tires on my commuter. No flats until a couple of weeks ago. Slow leak. Turned the tire inside out and used a magnifier to find suspicious breaks in the tire. found a spec and probed with a needle. Extracted a wire from a dremel wire wheel! Its curly feature must have wormed its way through the tire.

Good point. I had a brand new tube (Continental) a year ago where the core popped out after I pumped it up the first time! A couple of times, before I got it down tight. I don't know how but the adapter or pump was loosening it up and unscrewing it.

Besides small wires, look for extremely small triangular pieces of glass that only protrude through the rubber when the tire is in contact with the ground. That is when the puncture happens, then when you search or use tissue, you won't find it because it retracted back into the tire case.