mynameuk

hi

i ride a road bike with 25mm tyres. today i got a puncture and so replaced the tube as normal but i couldn't get the tyre to sit well and it took several attempts to get it 'round' after about 10k i got another puncture, this time a small hole on the inner side of the tube, just next to the valve. this time couldnt get the tyre on propery but was able to ride the 20k to the bike shop. the guy used soapy water to get the tyre to sit properly and all was well. rode home and as soon as i put the bike away i heard a hissing, another puncture this time is the same place just next to the valve. inspected both the tyre and the rim and there are no sharp shards or anything that would cause a puncture. i also cant get the tyre on again.

anyone got any ideas as to what is happening? is the tyre being 'out of shape' causing the puncture. im too afraid to even ride now as i doubt i would get 10k without another puncture.

thanks alot...

Retro Grouch 

Almost surely the manipulation required to make your tire round is what caused the damage to your tube. The good news is there's a good chance that the solution might be easier than you think.

The area immediately surrounding your inner tube's valve stem is thicker than the rest of the inner tube. If your tire beads rest on that thick spot your tire will never center. The solution is, after installing the tire on the rim but before inflating your inner tube, push your valve stem in toward the rim.

Hope that's all that it takes to fix it.

FBinNY 

Punctures on the rim side near the valve are fairly common with narrow rims, and tend to occur soon after a tire replacement. They're especially common with schrader valves in narrow rims.

The narrow rim combined with the thickness of the tire at the bead leaves a narrow gap for the valve to fit through. That leaves the base of the valve deep in the tire, and at full pressure the section of tube there blows down into the gap over stretching it and causing small tears.

Next time you mount a tire, start opposite the valve, and finish at or near the valve. Then push the valve deeper into the tire to pull out any trapped tube, inflate to 15psi (1atm) and inspect for even seating and correct. Now -- before inflating to full pressure, let enough air out that you can push the valve down (out of the rim) until you feel it bottom. (DO NOT pull the valve, because this can tear the rube from the base). Finish by inflating completely.

If you continue to have problems, look for tubes with long reinforced areas extending to either side about 2cm. Or you can make your own with the long oval oatches some patch kits include. Punch a hole for the valve and apply like any standard patch.

Wanderer

I finally get tocorrect you, FB. 15 psi would be + 1 atmosphere............... lol

Andrew R Stewart 

Well another might say that 1 atmosphere + 15psi will equal about 29psi Andy.

FBinNY 

Since 1atm = 14.7psi (rounded from 14.696) then for practical purposes it's equal to 15psi. (rounded from 14.696).

But you're right that 15psi is more than 1atm, but I figure that people don't have gauges that are accurate enough to make a difference, and in any case it was only an approximation, since I don't gauge for that, I inflate until the tire has enough shape to check for seating. I was going to type 5-10psi, but moved it up for ease of rounding from imperial, since the OP was in China.

You missed the real error. I should have said approximately 15psi, since no precision was needed.

They might but 1atm + 15psi = 29.7psi which rounds to 30, not 29, however 2atm - 29.4psi which rounds to 29.

berner

I once ended up having mysterious leaks around the valve stem. After replacing several tubes I figures out the rim, after being drilled for the valve stem, had rough aluminum shards sticking out that cut into the tube. I sanded the edge of the valve hole with a piece of sandpaper which solved the problem. Now I sand the valve hole in advance on any new rim.

ursle

Ah, a clue, take some linen and run it around the rim and tire to find any metal shreds, splinters etc.

Wanderer

Andy wins the prize! Since the first atmosphere is already here......

FBinNY 

Cute, but we need to get the standard nomenclature straight.

When referencing the mechanical effects of pressure in a vessel such as a tire, boiler, air tank, etc, the standard is to speak of psig or gauge pressure. More precisely it's the difference in pressure inside vs outside, or on the surface the pressure above 1atm. However it's common practice to drop the g and reference psi, bar or atm.

However, when discussing the chemical effects of pressure, or when gas mixing, we need to consider the absolute pressure which would include the gas inside the vessel if open to the outside or 1ata.

If you go back to my post, you'll note that I gave pressure in atm, not ata. (on the gauge pressure in atm = ata-1)

In fields such as scuba diving where both mechanical and chemical effects are of interest the pressure given can be ambiguous so it's common practice to clarify by using the reference pisg to indicate gauge, or differential vs. absolute pressure.

Wanderer

Since you equated it with 15 psig, in your orig post, maybe it needs correction......

I gotta stop this, its hard posting with my phone.....

RoadTire 

Now I'm really confused. Did you mean to say inflate to 15 psi or 29 psi in your original statement of inflating to 1atm? (that's a serious question)

FBinNY 

Everything I write in bicycle related posts is in atm, or psig meaning gauge pressure. That's true whether I write psi or psig, UNLESS I clearly say I'm speaking about absolute pressure (which I'd have no reason to in a bicycle forum).

So when I say 15psi, or 90 psi, or 1 atm or 6atm, I'm speaking about the pressure as measured with a gauge, the same way everybody here would be. The confusion exists only because Wanderer introduced the idea of absolute pressure, which has no place here.

BTW- the actual n umber is irrelevant since my suggestion was to inflate the tire enough to check seating, and there's a wide range that is fine. To my knowledge nobody checks the "check seating" pressure, they simply do some pump strokes until the tire takes shape, check seating, them inflate to riding pressure.

Carbonfiberboy 

OMG I learned something new! Maybe a couple times a year on 15mm inside measure rims I'd have this sort of "puncture" near the valve and see nothing wrong with the rim tape, etc. I'd put in another tube and usually patch the bad tube and not have this happen again for . . . maybe a year. If the hole were too close to the valve, I just threw the tube away. Never had it happen on a wider rim. I suspect it might be related to a particular style of valve reinforcement. These "punctures" didn't happen right away. I don't recall exactly, but these tubes might have been ridden on for weeks. Might have something to do with the tube squirming right where it was overstretched.

FBinNY 

Gee, I hope this isn't the first time you learned something new, and that you'll keep doing so.

I suspect that the the change in valve design from the one on the right with a large base flange to the current version (2nd from right)


was to reduce the base width so they would work properly with narrow clincher rims. Unfortunately the new design went through years of bond failures and base of the valve leaks until they (maybe) got it to hold up well.

Carbonfiberboy 

Well, having fixed hundreds of flats over 60 years I figured I had that down. Always room for improvement! Yes, they have gone to a much narrower valve base, so that now the most common tube failure is for the valve to pull out when one removes the pump.

sickz

if it hasn't been suggested... baby powder helps a lot of seating problems w/ the tube in the tire. preventing punctures etc.

hueyhoolihan

check your rim tape. a spoke hole may be showing.