gudel

I purchased new Specialized Armadillo (700x28) tires and new Specialized tubes (700x20/28).
Front tire installed OK. Installed the rear and as I was inflating the rear tire, and right about 80psi, the tire starts to bulge out of the rim. There's about 5-6 inches along the valve that pops out while everything else seems in place in the rim.

There's the rubber that covers the edge of the tire, that piece came off. I was thinking maybe that's the cause of the problem. First time I caught it, quickly deflated it. I removed tire and tube from the rim to see if there's anything stuck then reinstalled it again.

I pumped it to about 80psi and let it sit. It seems ok. Thinking it was good now, I pumped it to 100 psi (tire max rating, same as front tire pressure), wasn't quick enough, tire came off rim, it popped the tube.
Do I need a new tire? I'll try to take some pics tomorrow.

askrom

The part of the tube where the valve attaches to the tube has a thick ring of reinforcing rubber around it. Your problem is that this "fat" part is not actually sitting inside of the tire when you inflate the tube. When the tube is empty, the tire may appear to sit correctly, but in reality the bead is pinching the rubber around the valve.

What you have to do is, before inflating the tube but after setting both sides of the tire's bead into the rim, push the valve through the rim and up into the open cavity of the tire so that the fat reinforced part of the tube definitively pops into the cavity. This part of the tube has got to be inside the tire cavity, not pinched between the rim and the beads.

A test of whether you've done this right or not is whether or not the valve slides in and out freely when the tire is deflated and both beads are in the rim. If the valve can't move freely, it's being pinched.

Moose

Are you installing this on a hooked-bead rim?

sydney

^^^...I never ran into 700c that weren't.

gudel

I think you solved the problem. I installed new tube this morning, made sure that the value slides in and out easily. Inflated it, no more popping out! thanks askrom!

Moose

Now that you mention it...I don't suppose I have either. Now if you'll excuse me, I have some primo carpet to smoke.

DannoXYZ 

An extra step I like to take is to make sure there's no tube squeezing out. So after installing the tyre, I'll pump it up just enough to hold its form, like 1-2psi. Then pull the tyre away from one rim-edge and look at the gap between the tyre and rim. Then repeat for other side. You should be able to see all the way down to the base-tape. If there's a piece of a tube sticking out anywhere, I'll redo the job.

Another process I use is to barely pump up the tube so it's round, then install into tyre first. Then put the whole assembly onto the time. This eliminates the need to push upon the stem to unpinch the tube in that area.

candide

Dear Askrom

I just wanted to thank you, I am new to this and just had to replace two tubes in a row. I just couldn't understand how dumb I was to be unable to get this to work and started to despair. The devil is in the details, but thanks for showing me how to succeed and solving my problem. Have a great new year and many thanks for this forum too.

AEO

wow zombie thread.

cranky old road 

Well, we do encourage people to use the search function before starting a thread

ThermionicScott 

Yep, always heartwarming when old threads help newbies. .

Al1943

I miss Sydney.

JosefSvejk

This zombie still lives.

Just solved this problem on my son's bike. It was infuriating and leading to lots of punch punctures as I couldn't get above 40psi.

Thanks!

fietsbob

There are variations in how accurately the rim company and the tire company hit the mark of the ETRTO specs , for compatibillity..

sch

Yep worth revival just to resurrect the memory of Sidney.