soymateofeo

OK. I acquired a hybrid bike with 700 x 35 size tires with presta valves (my first presta valves btw). I got a flat and attempted to switch out the tube. What I did.

1. removed tire completely.
2. checked rim and tire well.
3. put tire on half way.
4. inserted presta valve stem through rim and screwed it to the rim.
5. inserted "completely deflated" tube into the tire.
6. pumped it a bit and checked around the rim.
7. filled it to 80 psi (as indicated on the tire)
8. BOOM! right where the stem is.

I said to myself, "Well that was stupid. I must have pinched it somewhere."
I did it again...damn near exactly the same and BOOM in the same spot.

I then took my rim and tire and tube to the lbs and told the mechanic what happened. He said the rim and tire were in great shape and that I might want to change 2 things.

change 1: inflate the tube a bit before you put it in the tire so there is no pinching.
change 2: add some talc to the tube and to the tire to help it slide in. He said that there is much more room in a 26 inch mtb width tire but less room for error in a thinner hybrid tire.

I did as instructed and the tire seems fine.

I'd appreciate any input on this because I've changed hundreds of tires from childhood until yesterday and have never had this problem but never had such a thin tire or presta valves.

soymateofeo

And I've changed shifters, straightened forks, overhauled bearings, and am defeated by a seemingly harmless tube. That's what I get for not observing lent I guess.

FBinNY 

Here's where you went wrong. You trapped the tube under the bead of the tire and when inflated it jacked the tire up over the wall of the rim.

Next time do not screw the valve ring on until after the tire is inflated for riding. Better save the ring for s fishing line weight, or other use, but don't use it on the tire at all.

Also partly inflate the tube to give it shape before stuffing it into the tire so you can't twist or trap it under the tire. Overall this makes mounting much easier.

Lastly, mount the tire starting opposite and work towards the valve. There's little risk of trapping the tube as you start and when you finish at the valve you can easily ensure that the tube is clear by pushing the valve up into the tire (taking the tube with it) then pulling it down to seat everything properly.

When you've finished partly inflate to about 30psi and spin the wheel to make sure the tire is evenly seated all the way around. Any low spot means that there's a high spot elsewhere possibly leading to a blowout. When you're confident that the tire's evenly seated inflate to full pressure and ride.

BTW- If you're using a PV in a rim drilled for Shrader, put a small piece of cloth reinforcing around the base of the valve. I used to use 2 of the little reinforcements they make for looseleaf note book pages for this job and they worked well to keep the edge of the hole from cutting the tube.

Nerull

If the failure happened right at the stem, #4 could be your issue. Do not screw the valve down to the rim. It puts a lot of stress on the valve as you inflate. You don't need the nut at all.

jimc101

Sound correct, if you are going to use a nut, it need to be tightned, but should be the last step after the tire is fully inflated and before putting the dust cap on.

davidad

After installing the other edge of the tire you should check to see that the tube is not under the tire bead. Then push on the stem to make sure it is not trapped there. I put the nut on the stem inside the tire to keep from pulling on the rubber at the stem. I very rarely have tube failure at the stem.

fuzz2050

It's handy to have the nut in case you need to do a roadside repair with a frame pump. Short of that, they don't do much, and they can certainly cause flats. It's not often, and in my experience it takes a perfect storm of conditions, but it can happen.

work4bike

This is what I do

1. remove tire completely.
2. check rim and tire well.
3. partially inflate tube and insert into tire. (all my spare tubes already have talc powder applied)
4. put tire/tube on rim and insert presta valve stem through rim hole.
5. screw on presta vlv nut. (I only put the nut on enough to allow me to install pump on presta valve -- do not screw nut any further).
6. pump it a bit and check around the rim.
7. fill it to 80 psi (as indicated on the tire)

You'll notice that the presta valve nut will separate from the rim as you inflate the tire; when that happens I do not retighten nut. The nut is just there so the presta valve is not pushed into the rim as you install the pump, never screw the nut completely onto the presta valve.

cyccommute 

Step 4 probably is your problem. The tube is thicker at the stem because of the reinforcement needed there. Once you get the bead in place ( I never preinflate, by the way), push the stem back into the tire so that the thicker reinforced part of the tube is inside the tire and not trapped under the bead. Don't push it so far in that you lose the stem but do push it far enough. Once the stem is seated properly, I put the nut on so that the nut holds the stem in place and allows you to push the pump on without pushing the stem back into the tire.

Like I said above, I never inflate the tube. It makes the installation a little harder. The talc may or may not help. I use it but I don't think it makes the installation easier. It makes removal later on easier because the tube doesn't bond to the tire.

The stuff about the 26" vs 700C tire is a bit of hooey.

FBinNY 

proving that there's more than one way to skin a cat. Pre-inflate the tube or not, start and end wherever you prefer.

No matter how you mount the tire, the key is to make sure the last bit of tube isn't trapped under the tires bead. If you end at the valve pushing it in and pulling it out again before inflating does that for you.

wrk101

+1 I manually inspect the bead area, all around the rim, both sides of course, to make sure none of the rim is caught under the tire bead. I never use talc. I do not use the nut on the stem. I put a little air into the tube prior to installing, not much.

JanMM

I used talc for years - decades - until I read on the internet (on BF, I think) that it really serves no purpose. Haven't used it for 5-6 years now and don't miss it.

DannoXYZ 

I think there's another problem. Somewhere between #3 and #6, you should've installed the 2nd half of the tyre!

soymateofeo

Sweet! I'll take this all to the lab and put it to work! Who knew presta was going to be my nemesis.