robtee92

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:

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

hueyhoolihan

"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:

prathmann

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.

Metacortex

You just answered your own question: When using straight side rims you should inflate the tires to 75psi or less.

LesterOfPuppets

32mm tires with 100 psi does seem rather extreme.

lopek77

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...

Bill Kapaun

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.

ThermionicScott 

+1. Just because the tire is strong enough to hold when pumped up to fantastically high pressures, doesn't mean that you necessarily should.

jyl

You should not be inflating 32 mm tires to anywhere near 100 psi.
Unnecessary and eliminates the advantages of wide tires.

Bill Kapaun

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.

Andrew R Stewart 

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.

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.

well biked

The only reliable solution is to back substantially off on the pressure, or use hook-edged rims.

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.

LesterOfPuppets

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.

LesterOfPuppets

Maybe you touched the inside of the rim with a greasy finger?

JohnDThompson 

I'd just run a wider tire at lower pressure and be done with it.

robtee92

Seems like it...

They're these tires rated to 95psi on the sidewall.


That seems to be the consensus ughhhh

Haha I've never heard of this what does this do?

LesterOfPuppets

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.

SkyDog75

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.

LesterOfPuppets

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

79pmooney

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.)

Ben

lopek77

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.

jyl

An oft posted guide to inflation

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