Tube pressure

[nickp]

I am having some trouble with my rear inner tube, i can't seem to get it to stay at the right pressure.

When i pump it up it is fine for a little while but after riding it for a few mins it loses a lot of pressure, so far i have replaced the inner tube, and also the tyre but it hasn't fixed the problem.

Any idea's.

TIA

 

[Gerry Attrick]

If its a Presta valve, are you screwing down the lock ring after inflating it?

 

[nickp]

If its a Presta valve, are you screwing down the lock ring after inflating it?

Yeah it's a presta valve, lock screw is nice and tight.

 

[MajorMantra]

If you replaced the tube without finding the origin then you may simply have punctured two successive tubes. You need to take the tube out and find out where it's leaking so you can patch it and you also need to find out why it punctured.

Check for debris and check that your rim tape is intact and that there are no spoke nipples poking through.

Matthew

 

[nickp]

I checked the first tube but found no punture, also checked the old tyre for debris.

This is a new tube and brand new tyre.

Cheers

 

[ColinJ]

Pump the tubes up and hold them underwater to see where the air is coming out. If it is from the seams, I'd suspect that they both come from a faulty batch. If you have holes elsewhere in the tubes, look very hard for glass or thorns embedded in the tyre. If you mark where the valve is on the tyre, you can work out where to examine the tyre for embedded objects (e.g. if the hole in a tube is 9 inches from the valve, then check the tyre 9 inches from where the valve was).

 

[nickp]

Both tubes are from different places and makes, both have been under water and have no leaks?

Tyres have been inspected and replaced.

This is a strange one.

Cheers

 

[ColinJ]

Both tubes are from different places and makes, both have been under water and have no leaks?

Tyres have been inspected and replaced.

This is a strange one.

Cheers

Somebody is playing silly buggers and letting your tyres down while you're not watching!

 

[nickp]

I wish that were true, then i could sort the problem out

 

[nickp]

Ok, last night checked inner tube and tyre again, pumped it this morning and went out for a ride, after about 2 miles it needed pumping up again, it's not going totally flat but enough for feel it.

It's really starting to bug me now.

 

[Bigtwin]

You have a pin-prick puncture, simple as.

These are too small to see underwater at the pressures we pump them up at to do this.

Either a tiny spike in your tyre or your rim tape has a tiny tear or similar.

Change the tape, and rub around the inside of the tyre with some fine wet and dry or similar.

 

[youngoldbloke]

Check the rim for sharpness around the valve hole. Inflate the tube and put pressure on the area around the valve, push it from side to side, and check for air escaping. I had a mystery slow puncture which turned out to be a failure of the junction of the valve with the tube, which only leaked when the tube was under stress as the wheel turned. If the rim is OK, you may be somehow stressing/pulling the valve/tube junction by your fitting or pumping technique. I always put the tube in part inflated, and hold the valve firm with the threaded collar, tightening as the tube is inflated. Before fully inflating I bounce the wheel to help the tube find its correct position in the tyre. Using talc or french chalk helps.

 

[nickp]

I will have a go at changing the rim tape, but the whole wheel has been striped, inspected and cleaned and i didn't find anything.

Thanks

 

[youngoldbloke]

Its a mystery - if all else fails maybe one of these? http://www.greentyre.co.uk/28inch.html

 

[ColinJ]

You have a pin-prick puncture, simple as.

These are too small to see underwater at the pressures we pump them up at to do this.

Ah yes. that rings a bell - I've had one of them in the past.

Instead of a stream of bubbles when the tube is under water, you have to watch long and hard and you will eventually see a single bubble form. If you wipe that off and keep on watching, eventually another will form. Over-inflating the tube will make the bubbles form more quickly.