Trueblood

I recently restored a 77' Zebrakenko Wind and purchased panasonic panaracer 27 X 1 1/4 tires for it. I am using it for my daily commuter.

The tires say 95 psi max on the sidewalls. I purchased an aergun x-1000 floor pump over the summer and used it for several months without incident with my touring bike running 700x28s. It has a pressure guage on it. I pumped the tires to 95 psi on the Zebra. All was going well until one night when I got home and had been off the bike for an hour or so. BANG, the rear tube ruptures - big gash on it. Hmm, so I thought, well, maybe that was due to using the old tube that came with the bike when I purchased it off of CL.

I then purchased several Continental Conti tubes - [Tour 28 (700C) ALL] - Schrader valves . The box says it is for 27 X 1 1/4 among several other sizes. I replaced the rear tube with one of the Continentals and left the original tube in the front tire. Weeks go by and then the other night, again AFTER I had arrived home, BANG - the front tube goes. A hole right on the valve itself - very strange. I replaced the front tube with another Continental.

At this point I lower the pressure on both tires to 90 PSI. Then tonight on the way home the rear tube goes again, one of the new Continentals, and again, a blowout.

I am thinking maybe the bead is not strong enough on these tires, but not sure. I had no issues with blowouts on the touring bike and using the aergun.

I think I will go to 80 PSI next.

Anyone have experience with the Panaracer tires or have any advice? Thanks.

icepick_trotsky 

Have you checked the usual suspects -- rim tape, glass in the tire, etc?

lord_athlon

The tube pops but the tire is fine?

ThermionicScott 

I'm betting it's the rims. If they're steel or otherwise have non-hooked sides, they won't hold onto the beads as well, no matter what the tires are rated.

nlerner

Yup, non-hooked bead rims plus Kevlar bead tires = blowouts above 70 psi or so.

Oldpeddaller

90 to 95 psi seems a very high pressure for tubes with Schraeder valves. Back in the day, Presta valves were termed "High Pressure" - and with non-hook beaded rims, high pressure meant anything from 70 to 90 psi. You may be over-inflating the tubes on those rims. The tyre manufacturers maximum pressure marked on the tyre side wall is just that - a maximum for that tyre casing, nothing more.

JohnDThompson 

+1 this.

juvela

+2

Trueblood

Wow, ok, thanks everyone, yes older Araya rims, perhaps original to the bike. Probably non-hooked. I would like to keep using the wheels as they are. Must of worked somehow back in the day. I was going to go down to 80 psi next but it sounds like 70 is the max on these.

ThermionicScott 

How much d'you weigh? Try out this calculator for a better starting point than just pumping 'em up to the max: Bicycle tire pressure calculator

Mos6502

I had the same problem with one of my bikes. Tube kept exploding when the tire was pumped up to the max pressure. Was an old rim without a lip for the bead on the tire. Max pressure is about 70-75 on these types of rims.

ramzilla

I've had several tubes do the same thing. A loud BANG when bike is resting. Then flat. Cheap Chinese tubes. I've been using "thorn proof" tubes on all my bikes for the last few years. They weigh a ton compared to ordinary tubes. But, I haven't had one explode on me yet. They hold 100 psi just fine.

eschlwc

hmm. that tells me my 23c paselas shouldn't be run at the 100psi i choose (83 percent of their 120 max), but at 73psi in the front and a whopping 116 in the rear.

i'll pass.

SkyDog75

Back in the day, tires were designed for straight-sided rims.

Bangs can't happen without space to explosively decompress, so if there's a bang, the tube is escaping the tire/rim cavity somehow. The tire could be blowing off the bead, the tube could be escaping past a rim strip into a double-wall rim, or probably a few other possibilities. I don't know how different tubes would fix that since even the thickest tube would blow out if unconstrained by tire and rim. By some voodoo, it seems to be working for you (and if it ain't broke, don't fix it), but I don't think choice of tubes is the root of Trueblood's problem.

ThermionicScott 

Try the 45%/55% weight distribution option and see if that matches your preference better. If I ran that site, I'd make it the default since 40/60 doesn't represent road bike weight distribution as well, and could cause issues for riding on really steep hills. And as I said, it's just a starting point, not the end-all-be-all.

3alarmer 

...+whatever. I've recently done this with Araya rims with what appears not to be a straight side, but a totally inadequate bump to retain the bead. I ran through two tubes and part of my remaining hearing before it occurred to me that maybe these were just barely old enough to be relatively straight sided rims (they are not 100% straight, but not much is there to hold the bead.)

My original tyres were some specialized low end things, so I switched to some Panaracers and lowered the pressures to 70psi rear, and 65psi front. So far, so good.

I'll probably just rebuild the wheels with a Sun rim when I get the chance.

juvela

one other thing you might check, just to rule it out, would be the manometer. you might make a comparison of its readings with a quality hand held one to see if they agree. chances are that it is fine but no harm in checking...

jimmuller 

I've had Schrader valves blow out spontaneously twice. (No, I don't mean the same valves blow out twice.) Once was while I was riding, once while the bike was sitting.

I've had once or two tires pop off of non-hooked-bead rims. I've never had a problem with hooked-bead rims. I run my 25mm Paselas at 115 to 120.

eschlwc

scott, that's a little closer -- it results in 85 in the front and 105 in the rear.

i wonder if a lot of you run the front much lower than the rear. i never really do, but maybe it's a good idea.?.

eschlwc

years ago when i ran michelin krylions, i had four blowouts like the op describes. they all happened after a ride. the tube was finally escaping between the rim and the bead. those tires were just really hard for me to seat properly. it's frustrating when you hear that rífle-like "bang!" when quietly pushing your bike through the chinese grocery.

glad i switched to wire bead paselas. hasn't happened since.

paselas are also a lot more cushy without giving up much in the way of speed.

ThermionicScott 

I try to keep my proselytism under control, but I'm a big fan. I've been running my 28's at 65/80 with a total weight of 190 lbs for something like 5 years now. My hands don't feel as beat up on rough roads and I have no pinch flats to report. Much nicer than when I pumped them up to an arbitrary 100psi because someone in my club told me to.

rhm

No. Whatever the problem is, the tube is not the cause. The rim, rim strip, and tire, together, are supposed to form a shell that the tube can expand into. If that shell fails in some way, the tube will rupture. if this doesn't make sense, reread what @SkyDog75 said.


I'm pretty sure Trueblood's problem is that the tire is not gripping the rim properly. It's a combination of an old straight sided rim, a new tire made for hooked rims, and high pressure. Possibly the tire wasn't seated right; no way to know that now. But if a tire has blown off a rim once, I tend to expect it to happen again.

Trueblood

With lower pressure, I hope not. The panaracer tires are 27x1 1/4, presumably manufactured for the older standard of wheels. My question is, what tire WOULD be designed for straight sided rims if not the panaracers? I have been careful in seating the tube and tire.

The Golden Boy 

I've got several wheels with Schraeder tubes... never had a problem at 90-105, but I do like to run them lower.

I can't say that I've done any sort of percentage thought... but 10-15 pounds lower than the max on the label.

FrenchFit 

Classic unhooked rim and/or non-wired bead. I have folding Panaracers that will blow off a modern rim well below max pressure, the bead is just too soft.

You simply have to run that combination of rim and tire well below max pressure. Or, you can swap out that old rim for replacement, like a Sun M13 or CR-18 rim, or buy tires with a tough wire bead, like Gatorskins.