chrisabn

Hey guys,

So today I got my pump (Serfas FP-35) in order to inflate the tires in my Globe Work 1 urban bike. The tires are 700x38c (Schrader valve) and the sidewall specifies to be inflated "75-100 psi". I pumped from 40 psi until the gauge marked "100" and then went away to do some chores. A couple of minutes later I hear a horrible deafening explosion, and come back to find my tire flat and the tube inside was ripped. The tire looks perfectly fine, though.

It probably helps to explain that I have never done this before, but what did I do wrong? Did I push the tire pressure too far? Everything on the bike is stock.

FBinNY 

Can't answer without seeing it, but 99% (maybe only 98%) of these types pf incidents involve the tire blowing off the rim.

Understand that the tube is only a rubber bladder, aka balloon, and has no mechanical strength to speak of. At anything over 5psi it will expand to fill all available space, and like any balloon will burst if not contained. It's the tire that provides the shape, the same way the stitched leather shapes a football.

If you're 100% sure the tire didn't come off the rim anyplace, open it up carefully, and remove the tube, and locate the burst spot. If it's on the rim side, look at the rim carefully and see if the rim strip isn't covering a hole completely (applies to double wall rims).

randomgear

Likely the tube was caught between the tire and the rim - partially inflate the tube before installing it, not using levers for installation and going around the wheel after the tire is installed pressing the tire in and confirming the tube isn't pinched between the tire bead and rim will help to prevent this. If you have a small sidewall cut in the tire a very similar thing can happen - check the tire in the area where the tube exploded for any small cuts.

PS, was that the gunshot like sound I heard at 9:10 this evening?

sreten

Hi,

75 psi is way too much for 38mm tyres nevermind 100psi for an average rider.
I don't know where the very silly numbers on some fatter tyres come from.

rgds, sreten.

For an average rider 60 to 65 psi rear and 50 to 55 psi front is ballpark for 38mm.

FBinNY 

Maybe we should wait and find out what happened before making pronouncements. If the tire is rated to 100psi, it's rated that high, and can hold the pressure. Whether or not that much pressure is desirable or not has nothing to do with it blowing out.

sreten

Hi,

I'm sorry, 100 psi in a 38mm tire is just silly unless your elephant.
I'm not pronouncing it as the cause, but I wouldn't be surprised.

The tyre would have to weigh a lot to hold 100psi reliably, the
~ recommended pressure for an average rider on 25mm tyres.

rgds, sreten.

https://www.schwalbe.co.uk/_webedit/u...cal%20Info.pdf

There is something very odd about a 38mm tyre marked 75 psi min to 100 psi max.

chrisabn

If we live close enough, it probably was. I thought someone was going to call the cops. (Sorry about the noise)

The pump started to feel really hard after 70-80. That was probably a good cue to stop.

The whole tube is still inside and the tire looks good around the edges. I don't even have my tools right now, so I'll just take it to the shop tomorrow and see what happened in there.

Thank you all for your kind insights - I'll post some replies tomorrow when I come out of the shop.

techsensei

Just because other tires have a lower rating is irrelevant. Just because a higher pressure may be unnecessary is irrelevant as well, because 75-100 psi has been approved by the manufacturer of the tire. Regardless, the tire should be able to hold much more pressure. That the tube exploded probably had very little to do with the high pressure; it is just as likely to have exploded at 65 psi.

randomgear

In Roslindale near Healy Playground?

BTW, Rozzie Bikes and the Boston Cyclist Union are having a free bike repair clinic at the Roslindale Farmer's Market in Adams Park this Saturday from 9:00am - 1:30pm. Ferris Wheels Bikes and Adi's Bike World should also be attending. You are welcome to stop on by, even if you are not from Rozzie.

sreten

Hi,

Its not irrelevant. Some tyres just have silly numbers on them
and only the gullible assume those numbers are always correct.

It doesn't change the fact 100psi max is a silly number for a 38mm
tyre, but 75psi as a minimum is an even sillier number for 38mm.

rgds, sreten.

FBinNY 

I don't know what you're smoking, but it's pretty powerful stuff. So tire companies that spend serious folding money on tooling to product a tire, don't know what their tire can take?

Regardless of whether you think it makes sense, I assure you that these companies know what pressures their products can take, and mark them with a rating well below that, leaving a healthy margin for manufacturing tolerances and user errors.

Shimagnolo

Putting 100psi in a 38mm tire would have me worrying more about the rim cracking, than the tire failing.

jmess

I had this happen to me twice with the same tire. You might want to clean the grove/j-hook where the clincher hooks to the rim. In my case I had been using talcum powder on my tubes. I think over a couple years some residue built up on the rim sidewall grove/j-hook which caused the clincher not to seat properly.

Bill Kapaun

Inspect the valve stem.
I had one that started with a "bubble" on it. Had it let go while the bike was inside a friends van cruising down the freeway.
Woke us both up!

cxwrench

If a tube explodes w/ a bang, it's operator error 99.999% of the time. Either the tire is cut and the installer didn't check, or the tube was pinched between the tire and the rim and the installer didn't check. If anyone can think of another reason I'm all ears.

FBinNY 

100psi in a 38mm tire puts roughly the same stress on a rim flanges as 150psi in 25mm tire. This is well within the rim's strength when new, but can become borderline when the rim is worn down to the indicator dots.

BTW- my commuter has 2" tires and I routinely inflate to 60psi in the rear, letting them bleed back to 50 over the week. This is comparable rim stress to a 38mm at 80psi, or a 25mm at 120. My rims are well worn, and probably at or near the wear limit (old rims without an indicator), so sometime within the next few months, I'll post what the remaining wall thickness was when they cracked.

joejack951

You'd be horrified then to learn that Specialized rates even their 700x47mm Infinity tires up to 100psi: https://www.specialized.com/us/en/ftb...tires/infinity

FrenchFit 

Big tires+cheaper rims+high pressure = happens all the time, the bead slips past the rim hook, tube explodes. Gets worse when the tire heats up or loosens up, so they tend to blow after a short ride. Just run them at lower pressure, even dropping into the 80s will probably be fine, though that' s more pressure than you should need with those tires.

fietsbob

reminded of a story about a 'slimed' tube blowing the tire off the rim ,


worst part was


finding the Cat, and getting it in the bathtub to wash the bright green goo off .

since the cat was nearby, 'supervising the job' , while the tire was being pumped up.

FBinNY 

Does the cat still supervise your tire pumping operation, or has he figured out that he doesn't want to be there while you inflate?

BTW- if he's still watching, do they sell safety gasses for cats?

fietsbob

Not my cat, just re telling the story.

so whether there was a learning based behavior change of the cat,
might be a topic for a student of psychology studies.

I expect PETA would not approve , of the testing procedure, if formally set-up, rather than accidental


as a child.. the family had a combination, all in one washer-dryer

the black cat liked the warmth after the drying cycle and would jump in,

but one time ,
the next load of laundry was loaded on top of the Sleeping Cat ..

the wash cycle had some loud noises of complaint. from the accidental occupant..

there, the washing off of the detergent from the cat, was also a second act of entertainment .

sreten

Hi,

Your quite right. Specialized seem to specialise in very silly numbers on their tyres.
75psi min to 100 psi max are stupid numbers for a 47mm tyre. No way is 75 psi
the safe minimum, you can go way beyond half that and still be safe.
(perhaps a typo, the 42mm or the 47mm).

100psi in a 47mm tyre is ludicrous, and IMO downright dangerous.

The 28mm is the most incomphrehensible :

"

The Infinity is a long-wearing, incredibly durable tire that's ideally suited for commuting, trekking, and street use. The deep recessed tread provides excellent traction through water and debris, while the rounded profile ensures stable, predictable handling in corners.

• Casing: 30 TPI
• Bead: wire
• Compound: 70a
• Flat Protection: Flak Jacket
• 26" x 1.75; psi 50-100; approximate weight 850g
• 700 x 28; psi 115-125; approximate weight 620g
• 700 x 32; psi 75-100; approximate weight 670g
• 700 x 35; psi 75-100; approximate weight 700g
• 700 x 38; psi 75-100; approximate weight 740g
• 700 x 42; psi 50-100; approximate weight 770g
• 700 x 47; psi 75-100; approximate weight 810g

"

115 psi to 125 psi for a 28mm tyre ? Everybody weighs very nearly the same ?
You can't go past 9% front and rear pressure difference ? utterly inane ....

Remember these are not road tyres, they are city tyres, 28mm typically about 75 psi.

Schwalbe put sensible pressures on their tyres, sensible minimum, sensible maximum.
You can see from the construction they describe how the various tyres vary somewhat.

I've no idea where Speciaized get their numbers from, but the recommended minimums
are way off anything to do with safety issues, and are silly high for all their tyres.
They seem to be pandering to the big psi numbers = quality utterly total myth.

rgds, sreten.

chrisabn

No, I'm a couple of blocks from Fenway Park. But I'll be sure to check the Roslindale event out. Thanks for the suggestion.

This became a pretty interesting topic. - I finally got back from school and the bike back from the shop. There was a 3 inch long rip on the tube - it literally just burst. The mechanic told me to set it at 80 psi - He saw a number mark somewhere in the tire - It gets me wondering exactly where, because I still have not seen that mark (inside?). To add to the confusion, Specialized lists the same 75-100 psi recommendations in their owner's manual. I'll be sure to contact Specialized, because a lot of people seem pretty surprised that a tire of this dimensions is meant to handle 100 psi (and the mechanic was as well).

davidad

The pressure on the sidewall of tires is 1/2 the pressure that will blow the tire off of the rim. The user most likely had a part of the tube under the tire bead allowing the tube to come out of the tire and pop.

sreten

Hi,

It is except when it isn't. I'd pay to watch somebody pump up a 47mm tyre with 100psi
on the sidewall to 200 psi and accept all bets at even odds that it will get to 200psi

rgds, sreten.