Weird tyre pressure

[Andy_G]

A couple of days ago i went for a ride(about 60 miles), pressure was 120psi so all is well, a few hours after i got home i went to check the psi and the rear tyre was soft(not fully deflated).
The screw was tight on the valve so i cant be that, the only other thing is about 40 miles in i was behind a car and i hit a pothole pretty hard with the back wheel.

Any ideas

 

[Andrew_Culture]

How much pressure had you lost? How old is the tube?

 

[Andy_G]

I lost at least half and the tube must be 3/4 months old

 

[Rickshaw Phil]

You've picked up a thorn but it's stayed in the hole so only losing pressure very slowly? That's happened to me a couple of times.

 

[Andrew_Culture]

You've picked up a thorn but it's stayed in the hole so only losing pressure very slowly? That's happened to me a couple of times.

This.

 

[ianrauk]

Yup, something in there.
Take the tyre off and run a babywipe or cleaning cloth inside of the tyre. It will snag if something is stuck in there.

 

[Andy_G]

Yup, something in there.
Take the tyre off and run a babywipe or cleaning cloth inside of the tyre. It will snag if something is stuck in there.

Cheers ill try that.

 

[ianrauk]

Cheers ill try that.

If you can't find a hole in the tube then it may be worth also doing the old inflated tube in a bucket of water trick.

 

[Davidc]

If what RP says isn't the cause (odds on it is) then look at the valve. Contamination (piece of grit etc.) or failure of the rubber in the works could be the issue.

If it is they're swappable. (I have a little plastic container with the business bit from old discarded tubes in it, and sometimes need one).

 

[Andy_G]

I tried that first and not a single bubble, the only thing I thought of was when I hit the hole maybe somehow it forced some air out somewhere

 

[fossyant]

Dodgy valve

 

[I like Skol]

the only thing I thought of was when I hit the hole maybe somehow it forced some air out somewhere

Definitely not this!

Dodgy valve

Maybe this, If you can't find any bubbles in the bucket of water (including from the valve) when you have pumped the tube as hard as you dare then it could well be the valve is passing air at high pressures so your tyre deflates to a certain point and then stays there. I always add a tiny spot of washing liquid to the water (as I do this test in the kitchen sink it is always close at hand ) as I find this breaks the waters surface tension so you get a better stream of bubbles rather than a larger one that clings to the tube and may be missed if the leak is really slow.

 

[e-rider]

some tubes have removeable valve cores such as Continental tubes - these are often not screwed in tight in the factory so this could be leaking. I always check mine before using. However, if you have non-removeable core tubes then this wont be your problem!!!

 

[HLaB]

A couple of days ago i went for a ride(about 60 miles), pressure was 120psi so all is well, a few hours after i got home i went to check the psi and the rear tyre was soft(not fully deflated).
The screw was tight on the valve so i cant be that, the only other thing is about 40 miles in i was behind a car and i hit a pothole pretty hard with the back wheel.

Any ideas

Plenty of p'tures (maybe the pinch from hitting that pothole) can cause a tiny hole/s in the tube which is only open when the tyre is at high pressure and when the pressure drops it closes and the tyre onlly goes down slowly thereafter.

 

[Davidc]

Plenty of p'tures (maybe the pinch from hitting that pothole) can cause a tiny hole/s in the tube which is only open when the tyre is at high pressure and when the pressure drops it closes and the tyre onlly goes down slowly thereafter.

I've met this, and on a couple of occasions have been unable to find the hole at all, so have replaced the tube.

There's a limit to how much time it's worth spending hunting for a problem in a tube which only costs £3 or £4 to replace! If the tube does it again my view is that it needs to be scrapped.