Flat tyre despite new inner tube?

[hiker biker]

Ok so here is the problem.

I got a flat on my tyre and the valve come clean off so I bought a new inner tube.

I pump tested it up and it seemed alright, except now fitted on my bike its not pumping up, it stays slightly inflated (enough to still create the wheel shape and stay in the inner tube) but it looks like I have a flat tyre.

So i pump it up and it inflates a bit, but not enough to go rock solid as it should, what more wierd is that when it fully deflates I can always pump it back up to the above state (half flat).

The tube is definitely the right size I just don't understand whats going on.

[JohnV]

When you tested the tube, what pressure did you pump it up to? First thing I would do is to check to see that the tube is properly placed inside the tire (the US version of tyre) and that there are no twists or snags anywhere on the tube. If all is well at that point and you still can't inflate it to its max pressure and you still have the old tube, remove the valve in the valve stem and replace it with the one from the old tube and see if it inflates properly.

[DaveM]

If you can pump it up and it holds air, but you just can't pump it up beyond a certain point, sounds like the pump is the problem or you aren't getting the pump head onto the valve stem solidly enough and it's slipping off as the pressure increases.

[RobAR]

As Dave suggested, your pump could very well be at fault.
If you can rule that one out, it may be that you got 2X Lucky. As in, two problems at the same time but, only focusing attention on the most obvious. It's not uncommon to have a small puncture that creates a slow leak that leads to tire slippage that slices the stem. See where I am going?
If you still have the object in the tire that caused the leak, you're going to repeat history.

[hiker biker]

Thanks for all responces.

ahaha I am from the uk I wouldn't be able to tell you the pressure I had pumped it to but I can describe it as almost what I would of needed when it was on the tyre.

well what caused the old flat was split valve whilst pumping it up and that was beyond repair.

yeah I don't know weither to check for puncture first, or get a new pump and then check puncture because when I pump it up outside the tyre it inflates, but not to rock solid state.

[JohnV]

Yes, it can be confusing and frustrated. My road bike is giving me a problem with the front tube. My pump is new, and it inflates my hybrid's tubes and my wife's bike tubes quite well. On the road bike, I can inflate the rear tube to 100 lbs. and as I inflate, the pressure indicator stays at the pressure marker until I pump it again, then it goes up to it's next pressure mark. The front tube never shows the pressure correctly and when I pump, the indicator starts to go up to the correct pressure then begins to drop down toward zero. I am pretty sure it is the Presta valve (which I hate) but I haven't figured out how to remove the valve core from the stem. Not even sure if it's worth the effort for the cost of a new tube. It's just hard to know if I have over inflated or not and I certainly don't want to blow a tube while riding.

[hiker biker]

(05-08-2011, 07:41 AM)JohnV Wrote:  Yes, it can be confusing and frustrated. My road bike is giving me a problem with the front tube. My pump is new, and it inflates my hybrid's tubes and my wife's bike tubes quite well. On the road bike, I can inflate the rear tube to 100 lbs. and as I inflate, the pressure indicator stays at the pressure marker until I pump it again, then it goes up to it's next pressure mark. The front tube never shows the pressure correctly and when I pump, the indicator starts to go up to the correct pressure then begins to drop down toward zero. I am pretty sure it is the Presta valve (which I hate) but I haven't figured out how to remove the valve core from the stem. Not even sure if it's worth the effort for the cost of a new tube. It's just hard to know if I have over inflated or not and I certainly don't want to blow a tube while riding.

Yeah thats my fear, burst tube whilst riding.

I was lucky enough to borrow a pump from a neighbour and turns out it was the pump. So I now know not to buy cheap ass pumps EVER again. time to invest in a decent one.

Thanks for the help guys