ransomtrek

I have read similar threads on this, but they don't seem to apply to my situation or answer my question. Here it is.
I had a blowout a while ago. Upon checking, it appeared that the tire came off the rim at one point, the tube bulged out, and POW! It created a 2 inch split down the tube. I thought it was an anomaly. I have cycled for years and this has never happened before. The tire was worn, so I decided to replace it. It seemed to fit a little to loosely on the rim (700x25).

New tire. Proper seating. Proper inflation. It worked great for a few weeks until this morning. After about 20 min. of biking, POW! Upon checking, the tire had come unseated at one point, the tube had bulged through, and a 1.5 inch split had occurred in the tube. Now I am getting nervous. I don't know what is causing this. The bike is in great shape (Trek 2100). Rims in great shape - recently trued and checked. Tire/tube properly installed. Proper pressure (120 psi). It can't be the obvious, as I know what I am doing.

What else can it be? I am at a loss for ideas.

Al1943

If any part of the tube is caught under the bead it can work its way out. I have had this happen 2 or 3 days after mounting a tire. It can happen if even the smallest amount of tube is between the bead and the bottom of the rim, doesn't have to be the side of the rim. Adding a small amount of air to the tube prior to mounting will help keep the tube inside the tire. Blowing through the valve with your mouth should be about right.

If your rims are old enough to pre-date hook-wall rims then they are not rated for pressure that high. But I doubt that your rims are that old, not on a 2100. The 120 psi should not be a problem.

I would visually check the rim where it hooks the bead.

Al

ransomtrek

Al, I agree with your ideas, but I am quite confident that the rims have hook-walls and that the tube is not pinched anywhere. What you suggest is exactly what I have learned to do as well. And, before I begin inflating any kind of real pressure, I always do a thorough pinch of the tire all the way around the bead on both sides to ensure that there is no part of the tube getting pinched. I had the mechanics at our local bike shop check out the rim as well and they saw nothing out of the ordinary.

I'll just have to keep my eye on it...

WMBIGS

When I first got my Bianchi, I went through three tubes in one ride. Got real nervous. The tires were a real loose fit to the rim. I bought some good quality tires and never suffered that again in thousands of miles. Try some other tires.

ransomtrek

Did that. My vredesteins were worn along the center bead, so I put on some nice Bontragers that fit tighter. Same thing happened this morning on the same rear wheel.

Al1943

Any chance that you got some defective tubes? It's rare but I have seen it.

Al

Sci-Fi

Go with a lower pressure for a few weeks...maybe 85-100psi. Had a similar problem with new tires. Kept blowing out right at the point where the tire had been hanging on the rack. Went with lower air pressure and that allowed the tire to go back to it's original shape and hook on to the rim properly. Now I can go max pressure w/o a problem.

curbtender

Maybe your pump/airgauge is malfunctioning?

Cadfael

Is it happening near the valve by any chance?

I messed up a few times fitting new tyres to my Mavic rims on my road bike, I simply could not get a tyre to fit without the tube popping out and exploding on me. However, I am used to fitting tyres to an MTB.. it is only recently I have used a road bike with a narrow slick tyre.

My mistake was tightening down the lock ring on the presta valve before I inflated the tyre. My LBS eventually showed me how to do it right. Leave the lock ring off, inflate the tyre partially, and push the valve in and out a few times to ensure it is not trapped.. and more importantly the tube is not trapped between the rim. Then fully inflate... THEN fit the lock ring.

stevage

My blowouts have all been caused by a bent bead. But you have a new tyre - though you don't mention what kind. I'm inclined to think "coincidence" so far, but why not try a different brand of tube or something?

stevage

>Then fully inflate... THEN fit the lock ring.

Well...one of the purposes of the ring is to avoid breaking the valve if hand pumping.

DannoXYZ 

Are you checking with no pressure in the tube? You need to let out some air so you can pull the tyre sideways enough to see down the gap between the tyre and rim-edge. You need to be able to see all the way down to the bead-seat area and see bare rim. And you can only pull the tyre sideways on one side at a time because you need to pull it over about 1".

As mentioned before, the valve-stem area is particularly troublesome. This is made worse if you start and stop your mounting at the valve-stem. I always start about 12" off to the side of the valve-stem and work over it on my way around. This completely eliminates the need to shove the valve-stem into the tyre to unpinch it because it's not pinched in the first place.

reueladhikari

Loose fitting tire, rim combos are just bad luck, I find. The 1st & 2nd times I mounted a Kevlar bead Marathon Supreme tire on a Velocity Synergy rim the tubes blew out. During the 3rd attempt I carefully monitored the seating with about 20psi air and wheel mounted on frame and it didn't blow. I've had a few 6/7 hour riding sessions on this back wheel with no problems, but I suspect at the height of summer it might just go BANG!

pmt

Or just switch to Road Tubeless and you'll never have a tube go Bang again.

Noobert

check your rim strip, see if its good, and also make sure it covers the spoke holes.

ransomtrek

Good thought, but I don't think a defective tube would cause it to rupture out of the tire, would it? Wouldn't it simply deflate?

ransomtrek

Yep... been done and it's in good shape.

ransomtrek

There's a thought.

ransomtrek

Yes, always.

ransomtrek

Good idea, but no. I am always careful to not lock the ring down until there it is sufficiently inflated.... and it seems to be popping off the rim on the opposite side of the valve stem. Of course, this has happened only twice now, so it's hard to say it is a consistent patter.

ransomtrek

@Sci-Fi - that is a great idea for the new tires. Although my tires were foldables and not hanging on a rack, there is still the possibility that a kink from the fold needs to be worked out. I did a long ride this morning with no problems. But that's the strange thing. I had biked for two weeks on the new tire with no problems whatsoever until a few mornings ago when it blew off the rim with a BANG. I'll stick to a little less pressure for now and see how it goes. Thanks.

Map tester

1. Did it happen at the same place on the rim both times?
2. If it is opposite from the valve, is it where the rim is joined together?

I would re-check the bead of the rim--could it be worn or something lodged in the rim to keep the tire bead from seating?

Cadfael

Accepted, I will not disagree with you on that. But you must at least partially inflate before locking it down, yes? Where the valve stem meets the tube it is a thicker rubber, and you need to make sure that this thick section is past the tyre beading (inside the tyre) before putting it under high pressure. If it is snagged under the beading the tyre is going to blow. So if you push the stem in and out a few times you can then make sure the raised and thick section is not trapped.

Stevage, all I can tell you is that I simply could fit a tyre on my bike without it blowing on me, I was beginning to feel a paranoid about it! But once I followed the instructions of my LBS I have had no problems... and my confidence is restored!

DannoXYZ 

What are the chances this is a 27" tyre on a 700c rim?

pgpdlr

Just for argument's sake, did you check your tire guage against another guage? Possibly your guage is reading "low" and you are overinflating.