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.

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.

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

Cheers for the replies :slight_smile:

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 before: -

(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 :slight_smile:

Re: more 29-er flat problems

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.

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.

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.

Re: Re: more 29-er flat problems

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 (I am now totally paranoid about punctures) 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.

I had a similar problem with my new 28" uni. The original tube popped loudly when I increased the pressure from 50lbs to 65lbs.

Inspecting the tire, I found shavings of metal (brass looking)inside the tire. I suspect the shavings came from the spoke nuts rubbing the rib while the spokes were being tuned.

What I did was wipe the inside of the tire clean, replace the rubber tube protector with that cloth ‘tube protector’ tape from the bike shop. Replaced the tube. When filling, fill ~30lbs, deflate, then fill again.

I’m no expert but I now have 70lbs in the tire now. Good luck.

Oh yeah, Those tires are loud when they pop. My ears were ringing for a few minutes.

Metal shavings can be left in the rim after manufacture. The drilling of the spoke holes can leave shavings either floating around between the walls of the rim or still attached to the spoke hole.

When the wheel is built it should have been checked to make sure there were no metal shavings in it. All of the spoke holes should have been checked to make sure they were clean and then compressed air blown through (carefully) to make sure no shavings were floating around in the walls of the rim.

A metal shaving from the rim is no match for most rim strips. A shaving can easily poke through a cloth or rubber rim strip. I got a flat on my freestyle unicycle back when it was new due to a metal shaving hiding under the rim tape.

I once had chronic flats on a road bike due to a tire with a bad bead. The tire passed a visual inspection, but replacing it fixed my problem. It had the “loud bang” problem due to the tube poking out the side of the tire as I approached a moderate tire pressure using a floor pump.

Re: more 29-er flat problems

On Sat, 14 Aug 2004 21:47:15 -0500, “onewheeldave” wrote:

>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.

I bought my Nimbus with a 35 mm tyre. Later I retrofitted the Big
Apple 2.35" with no problem. The rim’s inside width is only 22 mm and
the rimstrip states 26x1.75/2.125. It is a 700c wheel so the 26
puzzles me. The Big Apple is wider than 2.125 but it runs very fine. I
keep it at about 3 - 4 bar which is around 50 psi. I use it almost
exclusively for road rides for which it is excellent - no folding over
at that pressure.

Note that the Nimbus II frame (square crown) is OK for clearance, but
the round Nimbus I (28")doesn’t accept the 28 x 2.35 Big Apple.

Klaas Bil - Newsgroup Addict

I like the idea of not having to balance when out on a ride - joe

Re: more 29-er flat problems

onewheeldave Wrote:
> 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
>
> Dave your one wheel or shall I say tyre probably has a thorn or similer
> in it.Run your hand slowly around the inside of the tyre to try to
> locate it.


cheechee

I had some flat problems with the Big Apple, but that’s becuase I was going urban off road (no drops). I switched to the Nanorapter, with good results so far.

Billy

When Peter Bier, Steve Pavarno and I did The 42nd Traverse on 29ers Peter got 2 punctures. (As well as that I broke a cotterpin and had to walk out, but that’s another story.) Both punctures were pinch flats. The cure I’d recommend is to get a thicker walled 29" specific inner tube. A standard 28"/700Cx45 will be stretched to the point of being very thin inside a 29 inch tyre. This makes it very easy to get pinchflats, especially during offroad riding. There are at least three different 29" specific inner tubes available, one of which is made by WTB.

+0}[y

Another day, another puncture :slight_smile:

Felt this one go- an audible pop while riding up a hill.

Not a pinch flat this time, but a single hole facing the rim and right over a spoke.

I’m guessing that it was caused by the top of the spoke nipple which is one of the ones that got a bit shredded during an attempt to tighten it with a screwdriver last week.

I think my priority has to be to get a decent rim strip, the present one is thin rubber and doesn’t look as though it could be much use.

Being Sunday there was nowhere open to buy one so I’ve improvised my own with some wrapped newspaper.

Tony, I checked your link- those tubes look a bit expensive, and they only seem to come with presta valves with I try to avoid.

I think I’d be more inclined to get one when I’ve got a better understanding of why I’m getting so many punctures, especially as the punctures seem to be of different types- I’m suspecting that there’s more than one thing wrong here.

It’d be a shame to get a pricey tube to stop the pinch flats, and have it ruined by the normal punctures I’m also getting.

On the positive side I’ve learnt some useful stuff from this problem, an internet search turned up a method of getting tyres of the rim without using levers and on todays puncture Igot the tyre off easily with only my hands and also got it back on again without levers:)