I can't believe it... a flat tyre in my front room???



sergen

New Member
Jul 28, 2003
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Typical. My luck has been out this week.

My new TCR Composite arrives this morning - there's been months of waiting to get this thing. During the day at work all I can think about is "I so cannot wait until I get home tonight and finally ride this thing. I've been waiting so long".

So when I get home I fix the handlebar nice and tight, screw in my new Look pedals, attach the seatpost..... you get the picture.... by now I just cannot contain myslef with excitement.

Last thing I do is check the tyre pressure - I don't want to get a flat on my first ride, right? The bike came with Shimano Wheels and Hutchinson tyres - it said on the side of the tyres that the recommended pressure is 7 bar (or 100 psi).

Earlier on this week I got a brand new pump for the job - an 'Innovations Top Dog' pump that came with a gauge to check the pressure. It's one of those floor-mounted pumps that makes it easier to inflate the tyre.

And then the first weird thing happens. I unscrew the cap and twist the top of the valve. Before attaching the pump to the stem I press my finger down onto the stem to check the air is flowing OK. Suddenly the whole tyre has deflated - just like that! I'm not talking about a gradual deflation but an instantaneous one!

A little bemused, I figure that the stem must have some sort of 'quick deflate' mechanism - I've been riding the same no name steel frame bike for years so I have absolutely no idea what developments have occurred in modern bikes. I guess I must have pressed the valve stem in such a way to deflate it instantly.

In any case, I now attach the pump head over the stem and start pumping. I can see from the pressure gauge that air is now going into the tyre and things are starting to look good. But the needle on the gauge is nowhere near the recommended pressure of 100 psi or the max pressure of 110.... in fact it's not even at 80 yet. Nevertheless it's really starting to get difficult to pump the tyre so I keep forcing the pump.

All of a sudden..... BANG! The noise was so loud that my ears were ringing for about 60 seconds. And to compound matters I don't have any spare tubes.... guess I ain't going anywhere until tomorrow.

So can anyone figure out why this happened? Could it be that the pressure gauge on the pump is faulty? I hope not cos it's a reasonably expensive floor pump. Did I do something wrong? And what's up with the instant deflation that occurred?

Your frustratedly,

S
 
Just a thought - I had two recent flats that both occured while the bike was in the basement that turned out to be from slipped rim tape. The rim tape had folded over and the tube was getting down into the spoke hole that was now uncovered. Both times the tire had inflated fine and the bike was just sitting there when bang!sssssssss. The second time it happened I noticed that the hole in the tube was lovely and star shaped and I figured it out. The first time I just assumed I'd pinched the tube.

Ignore this if you know all about presta valves, but -a second thought is this - is this your first bike with presta tubes? It is quite easy to let all of the air out if you push the valve stem down. Then if you accidentally screwed the valve closed you may not have actually put any air in the tube (which would still be fine) at all. If you put the pump on with the valve closed it will go up to the amount of pressure that it takes to force the pump head off of the valve stem so you'll see the pressure gauge move, but you are only filling up the pump and hose. It will pop off of the valve with quite a bang and be very startling, but doesn't hurt the tube or tire as far as I know. If I am recalling correctly the open position for a presta tube is with the little nut screwed all of the way towards the top of the valve stem.
Good Luck
 
Eden said:
Just a thought - I had two recent flats that both occured while the bike was in the basement that turned out to be from slipped rim tape. The rim tape had folded over and the tube was getting down into the spoke hole that was now uncovered. Both times the tire had inflated fine and the bike was just sitting there when bang!sssssssss. The second time it happened I noticed that the hole in the tube was lovely and star shaped and I figured it out. The first time I just assumed I'd pinched the tube.

Ignore this if you know all about presta valves, but -a second thought is this - is this your first bike with presta tubes? It is quite easy to let all of the air out if you push the valve stem down. Then if you accidentally screwed the valve closed you may not have actually put any air in the tube (which would still be fine) at all. If you put the pump on with the valve closed it will go up to the amount of pressure that it takes to force the pump head off of the valve stem so you'll see the pressure gauge move, but you are only filling up the pump and hose. It will pop off of the valve with quite a bang and be very startling, but doesn't hurt the tube or tire as far as I know. If I am recalling correctly the open position for a presta tube is with the little nut screwed all of the way towards the top of the valve stem.
Good Luck

Hi Eden

this is most definitely my first experience of presta valves!

And unfortunately I am sure that the tube popped because the tyre was defintely filling with air.

Thinking about it, if I hadn't had the pump head fully clamped over the stem then it's possible that the gauge would be giving me inaccurate pressure readings? Could this have caused me to think that the pressure was only 80 when in fact it was way over 110?
 
Could be that the tube was twisted inside the rim, leaving a very small volume near the stem itself (which explains the rapid deflation)? When you pumped it up, the twist expanded and cut itself off.
 
sergen said:
Hi Eden

this is most definitely my first experience of presta valves!

And unfortunately I am sure that the tube popped because the tyre was defintely filling with air.

Thinking about it, if I hadn't had the pump head fully clamped over the stem then it's possible that the gauge would be giving me inaccurate pressure readings? Could this have caused me to think that the pressure was only 80 when in fact it was way over 110?
To tell the truth I'm just a wee thing (5'0", 103 lbs) and I don't think I would have the strength to actually burst a good tube even with a floor pump.....
It could have just been a bad tube. One of my team mates popped a brand new tube this weekend. It split right along a seam and it was the second one that had gone on her in just a few days. Looks like it was just a bad batch.
 
sergen said:
Thinking about it, if I hadn't had the pump head fully clamped over the stem then it's possible that the gauge would be giving me inaccurate pressure readings? Could this have caused me to think that the pressure was only 80 when in fact it was way over 110?
No, if the air doesn't go into the tube, the gauge will go up rapidly and the pump will get very difficult to push (springy feeling wanting to push the plunger back up). There's no way the pressure in the tube will be greater than the gauge reads if air is going into the tube. -- Edit: unless the gauge is broke. ;)
 
Weird stuff...could you tell us what the hole in the tube looks like? Where's the hole? What shape is the hole---slash, star? Is it at or near the valve? Is your tire bead damaged at all?

Having screwed up more than my share of tube replacements, with similarly explosive results, I've found this site invaluable for troubleshooting and haven't messed up since:

http://www.tokyocycling.com/troubleshoot/tire-n-tube.htm

For some reason, the site seems to be down, but here's the content, thanks to the Waybackmachine:

http://web.archive.org/web/20041010235140/http://www.tokyocycling.com/troubleshoot/tire-n-tube.htm
 
The rapid deflation may have just been the normal rate of deflating with presta valves. Since this is your first experience with presta, it may have seemed fast compared to what you used before (Schraeder, probably). Was the rate noticably faster in one wheel?

I recently had some tubes explode, and the problem was the bead not setting firmly in the rim. The tube would suddenty bulge out from between the tire and rim, inflate like a balloon, and explode with a deafening sound. It would happen so quickly that you had to be staring at the spot to notice what was happening. I went through 3 tubes this way, as my LBS kept telling me it was my mistake. The problem turned out to be incompatibility between the tire and rim, despite both being 700x28C. The rim measured about 1-1.5 mm smaller in diameter than what it was supposed to be (LBS measurement), though it was supposedly within the manufacturing tolerance range. I ended up having to go to a different 700x28C tire with a deeper bead and that fit a bit tighter.

As an additional suggestion to the good ones already offered, make sure you need to stretch the tire with some force to get it over the rim. By force, I mean it should be hard to do with just fingers, perhaps requiring tire irons. Make sure the tire doesn't slip easily on and off the rim. It's also possible your tube was pinched from the start, causing part of it to gradually balloon out the side as it was inflated.
 
Treat yourself to some spare tubes and, if you get bored one day, practice a few changes!

I remember the first tube I blew up with a pump - you are right the noise makes you jump about a mile in the air!
 
If you're as inept as I was when I first changed tubes, you should take care not to damage the bead when pushing the tire over the rim. I don't know whether sergen is running wire-bead tires, but if he is, damaging the rubber coating over the wire can result in a nasty surprise on the road. The bare bead slowly slowly rubs away a line into your tube as you ride, and you eventually end up with a surprising blowout with a single, long slash in the tube.

Take your time with your first tires, especially if they feel really tight. Shift the tire around the part of the rim it's already on to distribute the tension and stretch it out...
nbfman said:
As an additional suggestion to the good ones already offered, make sure you need to stretch the tire with some force to get it over the rim. By force, I mean it should be hard to do with just fingers, perhaps requiring tire irons. Make sure the tire doesn't slip easily on and off the rim. It's also possible your tube was pinched from the start, causing part of it to gradually balloon out the side as it was inflated.
 
It's nearly impossible to blow out a tube just by inflating it too much. You would need enough pressure to pull the tire bead off of the rim, which is typically more than 200psi. It's probably the rim tape, or perhaps a burr on the edge of the valve hole. I would also check the inside of the tire for debris. I've toasted a few tubes on inflation because small bits of glass or metal were left after fixing a puncture. It's unlikely with a new tire, but it's possible. As for the pressure issue, have you ever used that particular pump to inflate a tire to a high pressure? Some pumps have larger cylinder diameters than others, and while they push a lot of volume you really have to stand on them to get a high pressure.
 
I have to tell a story a friend of mine shared with me a long time ago. He had bought a new road bike from a local LBS and they had aired the tires up for him before he left. He was sitting at a stop light when a loud bang went off in the car. His first thought was that he had been shot. When he recovered from the shock he realized the tube in his new bike had blown. He went right back to the LBS and one of the spokes was too long and popped the tube. I don't know how this happens with a rim strip but I have no reason not to believe the story.