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Old 02-25-05, 09:23 AM   #1
Ebbtide
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Why do my tubes EXPLODE?

I went through three tubes in 15 minutes

I changed my worn tire for a new Conti. It is smooth and clean on the inside. My rim is clean and free of debris. Rim tape is in perfect condition. It is going on a 1982 27 inch clincher rim that appears to be "like new". Every time fill it up it explodes on the side opposite the valve stem. It blows the tire right off the rim

I got the bike second hand and it held air in the previous tire w/o problem. It almost seems as if the tire is not hooking on the bead.

It is a Japanese Bunchi Road bike.

Any idea on what might be causing this?
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Old 02-25-05, 09:28 AM   #2
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The thing that pops into my mind first is maybe the tire's not seating at the valve stem location properly. When mounting the tire, make sure you push the valve into the tire a bit. That will allow the tire to get past the thicker part of the tube where the valve stem is and seat into the hook bead.
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Old 02-25-05, 09:28 AM   #3
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What size are the original tires and what size are you installing?

Many 27" tires have almost no ability to hook the rim. You have to line it up perfectly as you inflate it.

One other problem could be with the rim. If it is damage it would casue the tire to hop off.

Inflate to 30psi and use your hands or a vise to line the tire up to the rim, go up 10psi and do it again. Repeat untill you get to the desired pressure.
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Old 02-25-05, 09:31 AM   #4
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Quote:
Originally Posted by nick burns
The thing that pops into my mind first is maybe the tire's not seating at the valve stem location properly. When mounting the tire, make sure you push the valve into the tire a bit. That will allow the tire to get past the thicker part of the tube where the valve stem is and seat into the hook bead.
His 27" tires and rims are probably flat sided, no hook.
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Old 02-25-05, 09:32 AM   #5
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Quote:
Originally Posted by r8ingbull
What size are the original tires and what size are you installing?

Many 27" tires have almost no ability to hook the rim. You have to line it up perfectly as you inflate it.

One other problem could be with the rim. If it is damage it would casue the tire to hop off.

Inflate to 30psi and use your hands or a vise to line the tire up to the rim, go up 10psi and do it again. Repeat untill you get to the desired pressure.

27x1 1/4 for the same. I'll give that a try when I get home. I did seem to notice that the "hook" on these rims seem to be machined into the inside of the rim's sidewall, not rolled over/pressed like most rims I've used. This is also on the rear wheel, I have not problems with the front, but maybe got lucky?

The rim does not appear dammaged.

Thanks so far.
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Old 02-25-05, 09:33 AM   #6
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Quote:
Originally Posted by r8ingbull

Many 27" tires have almost no ability to hook the rim. You have to line it up perfectly as you inflate it.
Wrong concept.Some 27" rims have no hook to retain the bead and are intended only for relatively low pressure.

Last edited by sydney; 02-25-05 at 09:49 AM.
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Old 02-25-05, 09:36 AM   #7
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Quote:
Originally Posted by sydney
Wrong concept.Some 27" rims have to hook to retain the bead and are intended only for relatively low pressure.
I wonder if thats it? At 80 psi it holds, up to 110 it blows. The rims are just as narrow my other road bikes. I assumed they would handle the same pressures. Did early 80s technology only allow for lower psi in tires? If so, any problems running Conti 1000s at low psi?

I will also add it takes about 3-4 minutes to explode after I fill it. Scared the hell out of me all three times too.

Last edited by Ebbtide; 02-25-05 at 09:50 AM.
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Old 02-25-05, 09:53 AM   #8
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I think perhaps the rims are manufactured for lower pressures, Most of the old school 27x1 1/4 tires I see have a max pressure rating of 90psi. I'm thinking maybe out and out "racers" back then were the ones using high pressure tires, if not "sew ups". But I might be a dumbass who's about to be flamed by a "retrogrouch"...
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Old 02-25-05, 10:01 AM   #9
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Quote:
Originally Posted by sydney
Wrong concept.Some 27" rims have no hook to retain the bead and are intended only for relatively low pressure.
If you get the tire seated right you can run them at 90psi. Actually it sometimes take 90-100psi to get these in place just right. It seems that the pressure from the tube holds the tire in place with friction between the rim and tire, so the more pressure you get they tend to fit better.

Does it pop off right away or does it sometimes take awhile?

It seems that there is no true standard for 27" tires and rims, some tires have a small bead, some have no bead, and some 27" rims have what appears to be a regular bead. I've always been able to get the tires to work. Sometimes they take awhile. Every 27" tire have seen is an ISO 630, so they fit, just not right.

Another thing, make sure the rim sidewall isn't bent or damaged. Make sure it's true also, that helps alot.

When you get the tire to 30psi make sure the markings on the tire are sticking out from the rim evenly all the way around, inflate slowly and wear earplugs.
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Old 02-25-05, 10:02 AM   #10
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http://www.bikeforums.net/archive/index.php/t-52039

I found this (^) thread, it answered my question. I'll try lower psi and walking the tire on.

Thanks,

Ebbtide
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Old 02-25-05, 10:09 AM   #11
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Most tires, probably a 27" tire, will say on the tire, Something like.......

"max pressure 80 psi ~ 110 with hook bead rim".

Meaning two maximum settings depending on if you have hook bead or not.

I'm just using those numbers as an example I have no idea what your tires actually are. But if this bike does not have hook beads, and it seems like it does not, use the lower setting. Your are right you may have different maximum ratings.

Also sometimes you may pinch a small part of the tube between the tire bead and the rim. This happens a lot. Before you inflate the tire to maximum pressure just put a few pounds in it and go around very carefully and move the side if the tire over a little and look for a small piece of tube pinched under the tire.
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