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How do I stop 630 32 rims from exploding all the time?

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How do I stop 630 32 rims from exploding all the time?

Old 03-01-15, 12:43 AM
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How do I stop 630 32 rims from exploding all the time?

Hello all I hope I'm not making any horrible mistakes on my first post.

I ride an old roadbike which has 630-32mm / 27 x 1-1/4" straight side rims. According toSheldon Brown:

Traditional 630 mm (27 inch) rims were straight side design, but in the late '70s they evolved to a "hook edge" design which would permit the use of higher pressures.

These days, many 630 mm (27 inch) tires are marked "For hook edge rims only" (some companies use the term "crochet type" instead of "hook edge"...this is the result of poor translation.)

The fact is that modern 630 mm (27 inch) tires will work on older straight-side rims, but they won't handle as much pressure as they are capable of with hook edge rims.

Generally, the "rule of thumb" for traditional 630 mm (27 inch) tires is that they should be inflated to 70-75 psi. This shouldn't be a problem with any tire, despite whatever disclaimer the manufacturer puts on the sidewall. However, if you're restricted to this pressure range, you probably shouldn't be running tires narrower than 1 1/8, or preferably 1 1/4, unless you're a very lightweight rider.
I've ridden this thing for a long time on the gumwall tires the bike was sold with at about 110 psi with no problems until the sidewalls gave way and I replaced the tires with non-gumwall tires, experienced a bunch of heart-stopping blowouts (thankfully never while riding it), put some gumwall tires on it and the problem went away for a while before coming back again recently. This is especially infuriating because this bike is my ONLY form of transportation besides walking.

I don't know what I'm doing wrong. I make sure the tube isn't bunched up or pinched between the tire and rim during installation. My plan after schlepping my butt over to the bike shop on foot to buy some tubes is to mark where on the tire and rim the herniation of the tube is happening, rotating the tire 180 degrees, putting on some earplugs, inflating to 90psi to see if it's a problem with the rim or the tire.

Thanks for taking your time to help me out
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Old 03-01-15, 01:08 AM
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"hook edge" (i'll use the terminology in the info you provided) rims can go 110 PSI easy. 75 PSI or thereabouts is about max for non edge rims. what kind do you have?

AFAIK, "hook edge" rims have been pretty standard now for about 35 years.

here's a "hook edge" rim:



and here's a cross-section showing a "hook edge" rim and tire and tube:





and here's a "non hook edge" rim:


Last edited by hueyhoolihan; 03-01-15 at 01:23 AM.
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Old 03-01-15, 01:30 AM
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The only advice I have is to try different tires to see if there's one that you can safely be run at the pressure you like, learn to live with a reduced pressure, or rebuild the wheels with hooked rims.

The OPs experience mirrors my own. Back when straight-sided rims were the norm there was no problem finding tires rated for over 100psi and they didn't suffer from such spontaneous blowouts even at 120 psi (which I used routinely on our tandem). But now that new rims are made with hooked sides the tire makers appear to have changed their tire designs slightly with the result that they no longer work reliably with straight-sided rims at pressures over about 80 psi.
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Old 03-01-15, 03:07 AM
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Originally Posted by robtee92
I ride an old roadbike which has 27 x 1-1/4" straight side rims...

...the bike was sold with at about 110 psi with no problems until the sidewalls gave way...
...I replaced the tires with non-gumwall tires, experienced a bunch of heart-stopping blowouts...
...put some gumwall tires on it and the problem went away for a while before coming back again recently.

According to Sheldon Brown:

The fact is that modern 630 mm (27 inch) tires will work on older straight-side rims, but they won't handle as much pressure as they are capable of with hook edge rims.

Generally, the "rule of thumb" for traditional 630 mm (27 inch) tires [on straight side rims] is that they should be inflated to 70-75 psi.
I don't know what I'm doing wrong.
You just answered your own question: When using straight side rims you should inflate the tires to 75psi or less.
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Old 03-01-15, 08:33 AM
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32mm tires with 100 psi does seem rather extreme.
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Old 03-01-15, 11:19 AM
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That's the beauty of a vintage stuff...beauty, not necessary durability or convenience. If you have so many issues with it, maybe it's time to upgrade your rims to something easier to maintain, and more worry free...
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Old 03-01-15, 11:33 AM
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Are you using wire bead tires?
Some cheaper tires may be "stretchy" or simply a bit oversize.

When inflating-
Work up the pressure in small increments, checking after about 5, 15, 30... PSI to make sure the tire bead is concentric with the rim.

BTW, you RIMS aren't exploding. The tube is.
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Old 03-01-15, 11:35 AM
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Originally Posted by LesterOfPuppets
32mm tires with 100 psi does seem rather extreme.
+1. Just because the tire is strong enough to hold when pumped up to fantastically high pressures, doesn't mean that you necessarily should.
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Old 03-01-15, 11:37 AM
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You should not be inflating 32 mm tires to anywhere near 100 psi.
Unnecessary and eliminates the advantages of wide tires.
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Old 03-01-15, 11:47 AM
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Originally Posted by jyl
You should not be inflating 32 mm tires to anywhere near 100 psi.
Unnecessary and eliminates the advantages of wide tires.
Depends on the weight of the rider.
I've never considered 27x1-1/4 to be wide, but for some reason I consider 622X32 somewhat wide???
Probably the difference in typical 27" rims and 700c rims which tend to vary from skinny road rims like my Sun Rim M13 II's to extra wide 29'r rims.
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Old 03-01-15, 12:13 PM
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Originally Posted by jyl
You should not be inflating 32 mm tires to anywhere near 100 psi.
Unnecessary and eliminates the advantages of wide tires.
Yet thousands of riders do without issues. As Bill k says it depends. When I tour I have close to 250# total weight, on our day riding tandem we have about 350# total weight. With 32mm tires (actual width, not label size) I'll run 105/110 F/R usually. Have for decades and many thousands of miles. Andy.
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Old 03-01-15, 12:15 PM
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Wow I'm surprised at all the replies I got

Originally Posted by Metacortex
You just answered your own question: When using straight side rims you should inflate the tires to 75psi or less.
The big giant point is that for months on the first set of ancient decaying gumwall tires, and weeks later on some brand new gumwall tires I was able to inflate it to 110psi with no problems, and now I'm not. This leads me to believe there's something wrong with the tire but close inspection doesn't reveal anything wrong.
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Old 03-01-15, 12:20 PM
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The only reliable solution is to back substantially off on the pressure, or use hook-edged rims.
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Old 03-01-15, 12:24 PM
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Part of an inspection is the actual application process. So by that definition your inspection does find something wrong. Tires can stretch, bead wise and casings can bulge both effect fit. Rims can get flat spots that upset the tire's mounting. Rim strips can shift to be under the tire bead.

BTW what are the current tires rated to, pressure wise? Andy.
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Old 03-01-15, 12:32 PM
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Originally Posted by robtee92
Wow I'm surprised at all the replies I got



The big giant point is that for months on the first set of ancient decaying gumwall tires, and weeks later on some brand new gumwall tires I was able to inflate it to 110psi with no problems, and now I'm not. This leads me to believe there's something wrong with the tire but close inspection doesn't reveal anything wrong.
Tire beads do tend to relax a bit after being on a rim for a while. So the new tire might have been just barely able to hold onto a rim at 110 psi when new, but has now relaxed to a point where that's not possible.

Once a tire has been blown off a rim, its bead has likely been relaxed quite a bit.
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Old 03-01-15, 12:36 PM
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Maybe you touched the inside of the rim with a greasy finger?
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Old 03-01-15, 12:38 PM
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I'd just run a wider tire at lower pressure and be done with it.
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Old 03-01-15, 12:44 PM
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Originally Posted by well biked
The only reliable solution is to back substantially off on the pressure, or use hook-edged rims.
Seems like it...

Originally Posted by Andrew R Stewart
Part of an inspection is the actual application process. So by that definition your inspection does find something wrong. Tires can stretch, bead wise and casings can bulge both effect fit. Rims can get flat spots that upset the tire's mounting. Rim strips can shift to be under the tire bead.

BTW what are the current tires rated to, pressure wise? Andy.
They're these tires rated to 95psi on the sidewall.


Originally Posted by LesterOfPuppets
Once a tire has been blown off a rim, its bead has likely been relaxed quite a bit.
That seems to be the consensus ughhhh

Originally Posted by LesterOfPuppets
Maybe you touched the inside of the rim with a greasy finger?
Haha I've never heard of this what does this do?
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Old 03-01-15, 12:52 PM
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Originally Posted by robtee92
Haha I've never heard of this what does this do?
A tire has much less willingness to hold onto a greasy or oily spot on the rim. Inside of the rim walls should be completely clean for best tire retention.
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Old 03-01-15, 01:14 PM
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Originally Posted by robtee92
The big giant point is that for months on the first set of ancient decaying gumwall tires, and weeks later on some brand new gumwall tires I was able to inflate it to 110psi with no problems, and now I'm not. This leads me to believe there's something wrong with the tire...
Not wrong, but different. Your new tires, like pretty much any new tires made today, are designed with hooked rims in mind. Sure, they'll work on straight-sided rims, but maybe not reliably at high pressures. Your old tires were probably designed for straight-sided rims. There may be something subtly different about their bead design that helps 'em hold to the straight-sided rim a bit better.
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Old 03-01-15, 01:26 PM
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Internet rumour has it that these hold tighter than Paselas. Not tan wall, but brownwall, at least.

https://www.biketiresdirect.com/prod...inch-road-tire
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Old 03-01-15, 02:09 PM
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I ride Paselas in 700c for about half my mileage but on new (Open Pro and Velocity) rims. I find them very consistent; enough so that it doesn't surprise me at all that if you had issues with one of those tires and your rims, that you would have the same issue on a regular basis.

There are tire-rim combos that don't work. This may be more prevalent with new tires and old-style rims, but it always been true. Another point that I haven't seen raised: are you checking carefully to make sure the bead is seated evenly all the way around on both sides? Panaracer puts a good, visible molded line on their tires that you should see (or not see any of depending on the bury of your bead) uniformly all the way around. I put ~20psi in my tire, hold the wheel by the axle ends and spin it, watching for any jumps or dips in that bead. Also to see the uniformity of the tread. Does it hop or move to one side? Only after I am satisfied that the tire is seated uniformly do I inflate it the rest of the way. This check may well be more important with the new tires (bigger, looser bead) and an old-style rim where all of the bead is against the middle portion of the rim with no reference to help guide it vertically. It will be will off the bottom of the rim cavity and there is no upper bead to guide it, so it is all up to the person installing the tire.

All that said, 32c Paselas and 100 pounds? You haven't said what your rider plus bike weighs, but that sounds like a lot! I ride those tires (700c) with 70 pounds on smooth roads. 80 psi is rock hard. I ride 60 pounds in the wet. (155# rider + 26# bike + say 15# stuff = 196#) (Andy's 350# at 110 psi ~= 62 psi at my weight.)

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Old 03-01-15, 02:50 PM
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Originally Posted by LesterOfPuppets
Maybe you touched the inside of the rim with a greasy finger?
Originally Posted by robtee92
Haha I've never heard of this what does this do?
100-110 PSI it's a lot of pressure that is trapped in a small space.
Car tires takes 20-40 PSI, and can kill when they explode.
Luckily bicycle tires don't have enough mass to kill, but they sure can hurt you.
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Old 03-01-15, 02:53 PM
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An oft posted guide to inflation

https://www.bikequarterly.com/images/TireDrop.pdf
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