Tyre Pressure Dropping

[morbihan]

Hey up.
I've been riding some 650b 42 mm tyres (tubes)
I have them pumped up to 55/60 psi and after a couple of days or so the pressure  drops down towards 20/25 psi.
I'm pretty new to wider rubber, and was aware that they do bleed pressure more quickly than narrower tyres at higher pressures; but this much???
Before I rip out the inner tubes and replace them, is this normal pressure loss?
No visible holes/damage on the tires.
ta.

[hubner]

Latex inner tubes would lose pressure like that, but butyl ones should take a week or two before you notice them getting softer.

[mrcharly-YHT]

I'm pretty new to wider rubber, and was aware that they do bleed pressure more quickly than narrower tyres at higher pressures; but this much???

Not in my experience.

In fact I've had tyres with a semi-sealed puncture (thorn stuck in the hole, drawing pin stuck in them) and not noticed for several hours of riding.

So I think you have a puncture or a leaky valve, my bet is on the latter. Wider tyres have a bigger volume and lower pressure forcing the air out; these factors combine to mean that they are less inclined to pressure drops than skinny tyres.

[Kim]

So I think you have a puncture or a leaky valve, my bet is on the latter. Wider tyres have a bigger volume and lower pressure forcing the air out; these factors combine to mean that they are less inclined to pressure drops than skinny tyres.

Agreed.

[Tigerbiten]

Another vote for a slow puncture/leaky valve.

One of my trailer tyres (42-406) has that type of problem, I need to put air in it every 4-5 days.
All my other 4 tyres (3x 42-406 & 1x 50-406) will go for a few weeks before I even need to think about putting air in then.
In that time they may have dropped from 70 to 60 psi.

[morbihan]

So not normal pressure loss them, thanks.
Its both tyres that are dropping (hence my suspicion it was normal) , so I guess there are two issues. Its likely either valves or slow punctures
Is there anything to do about a leaky valve beyond replacing the tubes?
It may be finally time to consider tubeless.

[mrcharly-YHT]

If you are using presta valves, the lower pressures sometimes doesn't push the valve back up to make a seal and it can be worthwhile making sure you tighten the knurled knob well.

If using schrader valves, dab a bit of spit over the valve, watch to see if it bubbles (or other liquid if you are fussy). If it is slowly leaking, sometimes firmly pushing the core in and quickly releasing it will seal. Or over pressure and release air.

[andrew_s]

If you use large-sized tubes (eg 27.5x1.75 to 2.5 MTB tubes), slow punctures will be a relatively common occurrence, be that thorns plugging the holes they've just made, or tiny fragments of glass only getting 90% of the way through the tube.

If you use lighter/narrower tubes, slow punctures will be pretty rare.

When you get the tubes out, pump them up to jumbo size so that you can find the holes, and by lining the mostly deflated tube up against the tyre, where the offending object is if it turns out not to be the valve. Don't lose track of how the tube lines up against the tyre, by turning it over or moving the tyre round the rim.

Blowing up to jumbo size stretches the hole along with the tube, so it's bigger and easier to find. Jumbo size might be 15 cm thick and 3 m in diameter. It's surprising how big you can get them before they go bang (unless there's a thin spot that develops into a local bul;ge).

[Biggsy]

It's strange to have it with both tyres at the same time, though.

Anyway, holes in tubes can be so small that you will only find them with the dunking-under-water method.  Sometimes even only one tiny bubble is emited every few seconds, so examine very slowly.  Or just replace the tubes if life is too short.

[rogerzilla]

You didn't use a CO2 inflator, did you?  CO2 seeps through rubber in a day or two.

[morbihan]

Thanks for the various feedback. I'll strip the tubes out and have a nosey. The wheels have done a bunch of KM on gravel/farm track. Never used CO2 to inflate, always a track pump.

[Tim Hall]

If you have valves with removable cores and they're leaking, remove the core, put a twist of PTFE tape on the thread and screw it back in tightly.

[hellymedic]

Removable Schraeder valve cores are replaceable and come in two lengths.

I can't say I've ever actually used the spare valve cores I had.

[Brucey]

this many posts and we don't know if they are presta tubes or Schrader ones....

BTW possible causes of slow punctures include that

a) the rim tape is duff and
b) that the rim is badly drilled ( a lot are these days), and the valve is not properly supported.

If the base of the valve starts to go bad, you can have a situation where the tyre loses most of its pressure fairly quickly, but it takes a lot longer to go completely flat.

cheers

[Kim]

If the base of the valve starts to go bad, you can have a situation where the tyre loses most of its pressure fairly quickly, but it takes a lot longer to go completely flat.

And the variation on that theme, where it holds pressure surprisingly well until either you disturb the valve, or the pressure drops low enough that the valve stem moves and the rest of the air spurts out in a convincing impression of a phantom puncture.

I find that base of the valve tends to be how tubes fail in small, high-pressure tyres that are reasonably puncture-proof.  There's not a lot else to go wrong, and the wiggling from frequently topping up the air eventually gets them.

[Brucey]

if the rim is drilled correctly (i.e. with a close-fitting hole for a presta valve in both the inner and outer wall of the rim) no amount of wiggling from pumping will ever damage the connection between the valve and the tube. All presta stems have a small ridge near the base that ought to be able to bear against the drilling in the inner wall of the rim.

Like I said before, badly drilled rims are depressingly commonplace; a very great number have a  hole that is too large drilled in the inner wall of the rim.

cheers

[mrcharly-YHT]

Like I said before, badly drilled rims are depressingly commonplace; a very great number have a  hole that is too large drilled in the inner wall of the rim.

cheers

And sharp bits that cut through tubes

[quixoticgeek]

When you get the tubes out, pump them up to jumbo size so that you can find the holes, and by lining the mostly deflated tube up against the tyre, where the offending object is if it turns out not to be the valve. Don't lose track of how the tube lines up against the tyre, by turning it over or moving the tyre round the rim.

Pro tip, when installing the tyres, line the manufacturers logo up with the valve, then you have an easy way of finding the matching point on the outer tyre as the inner tube when you've found the hole. Makes fixing punctures and finding the culprit item stuck in the outer SOOO much simpler.

J

[morbihan]

Well, it would appear that I have made a bit of a fool of myself here. (happens often, no drama)
I just deflated the first tire to switch out the tube and it felt suspiciously empty...then the valve  began to disappear into the rim when the lock nut was removed.
It seems the wheels have been set up tubeless. 
They were set up a few months ago on a new build, though I didn't request tubeless set up (no experience of it) but its a gravel tire (compass baby shoe pass) so I guess the builder thought that was the way to go.
Right, now to bone up on keeping air in a tubeless set up. 
Sorry to all of you who offered advise on bad info. I did take it all on board though for future use.
cheers.

[mrcharly-YHT]

lol that is hilarious, so you've been riding tubless and didn't even know it!

Possibly not even any sealant in there?

[morbihan]

lol that is hilarious, so you've been riding tubless and didn't even know it!

Possibly not even any sealant in there?

If there was I don't think there is any more. Nothing came out the valve.

[psyclist]

It may be finally time to consider tubeless.

Rather prophetic 

Somebody else posted a similar experience recently, but in reverse. Their tubeless setup turned out to include an inner tube.

[Brucey]

It may be finally time to consider tubeless.

Rather prophetic 

Somebody else posted a similar experience recently, but in reverse. Their tubeless setup turned out to include an inner tube.

they didn't notice any benefit, but presumably would have noticed had the tyres gone down by themselves, as tubeless ones often do. 

Is it my imagination or is 'normal behaviour for tubeless' about the same as, er,  having an actual puncture with a tubed tyre....?....

cheers
 

[Bolt]

It may be finally time to consider tubeless.

Rather prophetic 

Somebody else posted a similar experience recently, but in reverse. Their tubeless setup turned out to include an inner tube.

  Ha, that was me   I wonder how many others there are unknowingly riding "tubeless" with a tube, or "tubed" without a tube?

Good luck with the reinflation Morbihan, do let us know how you get on!

[andrew_s]

It seems that there are two versions of the Compass Babyshoe Pass tyre - regular and tubeless compatible (with a TC suffix on the name).
Vague memory informs me that people used to run regular Compass tyres as tubeless, and there was leakage through the sidewalls at a rate high enough to be obvious, but not so high as to prevent it working.

Maybe the bike shop fitted the wrong version?

[edit]
The blurb implies that the difference is the bead shape, so maybe the skinwalls are still a bit leaky. Sealant wouldn't get on the sidewalls unless you take action.