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more 29-er flat problems
Having established on a different thread that my recent, very frequuent, 29-er punctures were probably pinch flats caused by too low tyre pressure, I bought a track pump with built in guage. A few puncture free rides at around 50 psi seemed to have resolved the problem. The only down point was a few days ago when I removed the tyre to do some wheel truing. I decided to inflate it to 65 psi, the max on the tyres range; just before getting to 65 there was a really loud bang as the tube exploded! New tube and back down to 50-55 psi. Then today I got another puncture. Though I'd just bought yet another spare 700x45c tube I decided to do a repair on the damaged one, partly to save the hassle of having to take the wheel off. It went OK, then I inflated the tube, no track pump available here so I did my best with the hand pump, knowing that I wouldn't get it up to 50 psi. I decided to get the tyre as hard as possible- as soon as I'd finished there was a nasty sound of air escaping, and it deflated in seconds. Annoyed now I took the tube out again to find another hole had appeared in a different place! How could this happen without even riding the thing? As the hole was near the seam I decided to switch in the spare, and managed to ride home on it without incident. ------------- Can anyone offer useful insights into this problem, because I'm deeply confused and on the verge of giving up 29-ing, if only because I've bought four tubes (and a track pump) this month alone and can't justify the expense. My thoughts are that I do need to keep the pressure up with the track pump to avoid pinch flats, but also that maybe I need to stay away from the max of 65 psi. So I'm currently going to stay at 40-45 psi and see what happens. Would it be true to say that, given pressure is not so low that pinch flats are a problem, that going much higher makes normal punctures more likely? Also, as the tyre ratings are meant for a bike, couldn't it be the case that they would not apply when used on a unicycle, as, being one wheeled, there will be around twice the stress on it? Can anyone briefly explain what causes a pinch flat; I know the normal explanation is that it's when the tube gets trapped between rim and tyre, but, assuming that the tube is installed properly, how can this occur. Certainly my flats seem to be happening on normal riding i.e. not when dropping off curbs etc. Has anyone else had problems with excessive 29 flats? One of my theories is that maybe the tubes are faulty, possibly sat in the shop too long; although this is no help as tubes don't come with a sell by date. Another possibility is that, because my rim isn't designed for 29-ing (it's the old style nimbus 700c and consequently quite narrow) that this is causing the punctures. Although this wouldn't explain why it was OK during my last big 29-er phase at the beginning of this year, when I was riding every day for around a month and don't recall any flats. -- onewheeldave - Semi Skilled Unicyclist "He's also been known to indulge in a spot of flame juggling - but it's the Muni that really fires him up." ------------------------------------------------------------------------ onewheeldave's Profile: http://www.unicyclist.com/profile/874 View this thread: http://www.unicyclist.com/thread/34547 |
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#2
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Hi, Dave, I had similar problems on a tandem once, and also on my MUni. A pinch flat is caused by pinching the tube between the rim and something else. So if you ride with low pressure, the tube and tyre will distort all over the place and occasionally the tube will get trapped. A higher pressure will usually prevent this, unles the tube and tyre are too wide for the rim in which case you might not eliminate it entirely. The loud bang implies that the pressure caused or exacerbated a problem. I've had threeloud bang deflations on a unicycle. On the first occasion, the tube was too long for the wheel size, and the manufacturer had folded it abit to make it fit! I pumped it up to hard (60 ish?) and rode for a while, hit a bump, and BANG! This caused a long jagged tear in the tube. The second occasion whas when the tube had slipped round a bit and was dragging the valve into a diagonal position. The valve tore out. The third was years ago when I inflated a cheap tube/tyre combination with a track pump then parked the unicycle in the sun! You should easily be able to get a pressure of 60 or more psi with a decent hand pump. A track pump just makes it easier. I doubt that you could get enough pressure to burst a tube encased in a tyre. When I search for punctures and have no water supply, I remove the tube and pump it to 3 times its working diameter (approx.) and this has never split one yet. A tube properly positioned in a tyre won't stretch or distort, so it shouldn't burst. I wonder if you have a concealed sharp object either in the tread of the tyre, or in the rim tape. Alternatively, do you have a spoke that's a bit too long, or has a sharp end? is your rim tape seated properly? I cured the tandem problem and the MUni problem (repeated unexplained punctures) simply by replacing the tyre and tube. No doubt in each case there was a tiny tip of a thorn embedded in the tyre casing or something. -- Mikefule - Roland Hope School of Unicycling Everyone should be fatuous for 15 minutes. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/34547 |
#3
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Hi, Dave, I had similar problems on a tandem once, and also on my MUni. A pinch flat is caused by pinching the tube between the rim and something else. So if you ride with low pressure, the tube and tyre will distort all over the place and occasionally the tube will get trapped. A higher pressure will usually prevent this, unles the tube and tyre are too wide for the rim in which case you might not eliminate it entirely. The loud bang implies that the pressure caused or exacerbated a problem. I've had threeloud bang deflations on a unicycle. On the first occasion, the tube was too long for the wheel size, and the manufacturer had folded it abit to make it fit! I pumped it up to hard (60 ish?) and rode for a while, hit a bump, and BANG! This caused a long jagged tear in the tube. The second occasion whas when the tube had slipped round a bit and was dragging the valve into a diagonal position. The valve tore out. The third was years ago when I inflated a cheap tube/tyre combination with a track pump then parked the unicycle in the sun! You should easily be able to get a pressure of 60 or more psi with a decent hand pump. A track pump just makes it easier. I doubt that you could get enough pressure to burst a tube encased in a tyre. When I search for punctures and have no water supply, I remove the tube and pump it to 3 times its working diameter (approx.) and this has never split one yet. A tube properly positioned in a tyre won't stretch or distort, so it shouldn't burst. I wonder if you have a concealed sharp object either in the tread of the tyre, or in the rim tape. Alternatively, do you have a spoke that's a bit too long, or has a sharp end? is your rim tape seated properly? I cured the tandem problem and the MUni problem (repeated unexplained punctures) simply by replacing the tyre and tube. No doubt in each case there was a tiny tip of a thorn embedded in the tyre casing or something. -- Mikefule - Roland Hope School of Unicycling Everyone should be fatuous for 15 minutes. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/34547 |
#4
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Hi, Dave, I had similar problems on a tandem once, and also on my MUni. A pinch flat is caused by pinching the tube between the rim and something else. So if you ride with low pressure, the tube and tyre will distort all over the place and occasionally the tube will get trapped. A higher pressure will usually prevent this, unles the tube and tyre are too wide for the rim in which case you might not eliminate it entirely. The loud bang implies that the pressure caused or exacerbated a problem. I've had threeloud bang deflations on a unicycle. On the first occasion, the tube was too long for the wheel size, and the manufacturer had folded it abit to make it fit! I pumped it up to hard (60 ish?) and rode for a while, hit a bump, and BANG! This caused a long jagged tear in the tube. The second occasion whas when the tube had slipped round a bit and was dragging the valve into a diagonal position. The valve tore out. The third was years ago when I inflated a cheap tube/tyre combination with a track pump then parked the unicycle in the sun! You should easily be able to get a pressure of 60 or more psi with a decent hand pump. A track pump just makes it easier. I doubt that you could get enough pressure to burst a tube encased in a tyre. When I search for punctures and have no water supply, I remove the tube and pump it to 3 times its working diameter (approx.) and this has never split one yet. A tube properly positioned in a tyre won't stretch or distort, so it shouldn't burst. I wonder if you have a concealed sharp object either in the tread of the tyre, or in the rim tape. Alternatively, do you have a spoke that's a bit too long, or has a sharp end? is your rim tape seated properly? I cured the tandem problem and the MUni problem (repeated unexplained punctures) simply by replacing the tyre and tube. No doubt in each case there was a tiny tip of a thorn embedded in the tyre casing or something. -- Mikefule - Roland Hope School of Unicycling Everyone should be fatuous for 15 minutes. ------------------------------------------------------------------------ Mikefule's Profile: http://www.unicyclist.com/profile/879 View this thread: http://www.unicyclist.com/thread/34547 |
#5
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I run my 29er at 65-70 each time I pump it up and then ride it till it goes down to about 35-40. The big apple can take at least 70psi without problems. There must be something odd happening with your uni. If you can wait till mid/late september, there'll hopefully be a ride in nottingham organised by me, bring it down then and we'll have a look at it. Joe -- joemarshall - dumb blonde ------------------------------------------------------------------------ joemarshall's Profile: http://www.unicyclist.com/profile/1545 View this thread: http://www.unicyclist.com/thread/34547 |
#6
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I run my 29er at 65-70 each time I pump it up and then ride it till it goes down to about 35-40. The big apple can take at least 70psi without problems. There must be something odd happening with your uni. If you can wait till mid/late september, there'll hopefully be a ride in nottingham organised by me, bring it down then and we'll have a look at it. Joe -- joemarshall - dumb blonde ------------------------------------------------------------------------ joemarshall's Profile: http://www.unicyclist.com/profile/1545 View this thread: http://www.unicyclist.com/thread/34547 |
#7
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I run my 29er at 65-70 each time I pump it up and then ride it till it goes down to about 35-40. The big apple can take at least 70psi without problems. There must be something odd happening with your uni. If you can wait till mid/late september, there'll hopefully be a ride in nottingham organised by me, bring it down then and we'll have a look at it. Joe -- joemarshall - dumb blonde ------------------------------------------------------------------------ joemarshall's Profile: http://www.unicyclist.com/profile/1545 View this thread: http://www.unicyclist.com/thread/34547 |
#8
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Cheers for the replies Mike- I've had a few good inspections of the rim and tyre and found nothing, but if it happens again I'll take everything apart at home and give it a good going over. I do wonder if there is a problem with the tyre- it is pretty old. I'm tempted to go back to my old 45 mm before buying another 29-er tyre and see if that results in no punctures. Joe- my tyre is a Notos, not a Big apple, but you're right, I shouldn't be getting this many punctures. -------------- I found this on the web, it's got some of the usual ideas plus a couple I've not heard befo - http://tinyurl.com/55su4 (summary of the article is 'Wide rim + chalk in tyre + Duck tape rim strip = happiness') The chalk idea is interesting because I used to do a similar thing with talcum power sprayed liberally in the tyre of my muni; for a different reason- my valve kept going to a 45 degree angle after a bit of riding and I was told that talc would stop it by providing lubrication for the inner. Punctures on my muni are very rare and I wonder if this could be due to the talc. I have noticed on 29-er that the inner does actually stick to the tyre, so maybe chalk dust, as the article suggests, would help. One good thing about this is that I'm getting good at fixing punctures -- onewheeldave - Semi Skilled Unicyclist "He's also been known to indulge in a spot of flame juggling - but it's the Muni that really fires him up." ------------------------------------------------------------------------ onewheeldave's Profile: http://www.unicyclist.com/profile/874 View this thread: http://www.unicyclist.com/thread/34547 |
#9
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onewheeldave wrote: *... just before getting to 65 there was a really loud bang as the tube exploded! * Was the tube sticking out from between the rim an the tire? If so, I did the same thing when I put a Big Apple on a 700c rim. It's caused by two things - an improperly seated tire and too much pressure. The bead of the tire has a wire in it to keep it from stretching. If the bead is evenly seated under the hook of the rim all the way around then the tire pressure pushes it evenly into the rim and it's cool. If it's not hooked well at one spot then the tire pulls out at that point and releases the rim to open air. Blamo! The cure is to a) not overpressure the tire (usually 20-30 psi higher than the number on the casing, which is why I got fooled. The Big Apple went at 60 psi.), and b) seat the tire well. This is quite simple to do - put 3-5 psi into the tire, just enough to firm it up, then slowly spin the wheel and look at the bead. Is it even all the way around? If not, then push/mush the bead around until it is. Then raise the pressure to where you want it. If the bead isn't set right the tire will blow well below it's max pressure. onewheeldave wrote: *Would it be true to say that, given pressure is not so low that pinch flats are a problem, that going much higher makes normal punctures more likely? Also, as the tyre ratings are meant for a bike, couldn't it be the case that they would not apply when used on a unicycle, as, being one wheeled, there will be around twice the stress on it? * You're about right at 50 psi. Just get the bead to seat right. If it just won't seat right then it's a bad combination of tire and rim. onewheeldave wrote: *Can anyone briefly explain what causes a pinch flat; * The sidewall of the tire bulges out when the tire is compressed, part of the tube goes with it, and the rim pushes the part of the tire just above the bead through both layers of tube. Hence the nickname "snake-bite" flat. There are usually two holes or slots. -- cyberbellum - Level 1.0 rider! I was standing in the park wondering why frisbees get bigger as they get closer. Then it hit me. ------------------------------------------------------------------------ cyberbellum's Profile: http://www.unicyclist.com/profile/4550 View this thread: http://www.unicyclist.com/thread/34547 |
#10
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cyberbellum wrote: * Was the tube sticking out from between the rim an the tire? If so, I did the same thing when I put a Big Apple on a 700c rim. * I now suspect it was, for two reasons- 1. a page I found on my web search expressed the view that a explosion would be impossible if the tube was properly in the tyre, as a contained tube can only leak, not pop loudly. 2. tonight I decided to follow the advice mentioned above and put loads of talc powder into my tyre and on the tube, this meant deflating the tube, taking off the tyre etc. When I put everything back and started to reinflate it i was extra observant and noticed that, near the valve, the tyre wasn't seated properly and, had I not noticed it, I suspect that the tube would have poked out as the pressure increased. This is probably what happened previously. ------------------- Concerning Big Apples- is anyone here using them successfully on a Nimbus 700c (or similar) rim? One of my possible future upgrades was going to be getting the new 29-er Nimbus frame and putting a Big Apple in, but I wonder if it will work without a wider rim. -- onewheeldave - Semi Skilled Unicyclist "He's also been known to indulge in a spot of flame juggling - but it's the Muni that really fires him up." ------------------------------------------------------------------------ onewheeldave's Profile: http://www.unicyclist.com/profile/874 View this thread: http://www.unicyclist.com/thread/34547 |
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