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Cat 6 rider
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Discussion Starter · #1 ·
There was a discussion not too long ago about whether it was even possible for a bike tire to have a blowout (or whether it should be called a blow-off). Regardless of the nomenclature I had one on Sunday, and can’t figure out why. Before the ride I inflated both tires to 120psi- they’re Specialized All Conditions Pros (23mm front, 25mm back) which have a recommended inflation of 115-125psi, so I was right in the middle. I went out the Iron Horse trail (paved) from Walnut Creek to San Ramon- a very gentle climb, 200 feet or so in 10 miles.

There was a miserable headwind, and with the slight grade it felt like I was standing still. I thought maybe I had a tire going down. I actually checked both tires by feel a couple of times on the way up- they were both fine. At 15 miles I turned back, but this was hardly a technical descent- a lot of stop signs, but nothing that made me think I might be overheating the rims. At 27 miles I was cruising along at just over 20MPH when I came to a red light, stopped, waited about a minute for it to turn green, started up, and BANG! The front tube blew. It was ripped ten inches along the inside where it sits against the rim tape. The rip was near, but not on, the tube’s seam. In the middle of the rip was a section about an inch long and an eighth inch wide where a piece of rubber was blown completely off the tube. I suspect this is where it started. I never did find it.

The rim tape was still in place, in good condition, and perfectly smooth where the rip was. The tube was the correct size for the tire. There were no impacts to speak of. The tube probably had about 750 miles on it.

Anybody have any ideas what might have caused it, or is it just one of those things? I think I’ve eliminated all the easy answers, but I sure don’t want that to happen at speed.

I’m going to try to attach some photos.
 

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Do you check for pinched tubes?

Assuming that there was no damage to the tire (no sidewall tears) you probably pinched the tube. Whenever you mount a tire, go around the tire looking between the bead and the rim to make sure you don't have some tube sticking out. If you do, you'll need to work the tube until it's fully under the tire. Tube must be checked prior to inflation.

I usually check the tube for pinches, then I inflate to 80 lbs, deflate, and then inflate all the way up to my desired pressure (110).

There are also other reasons - but they all pretty much have to do with how the tube was mounted inside the tire.
 

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usually this is caused by a tube being inserted wrong. using tire irons to put that tire on sometimes causes a twist in the tube. I had this issue acouple of times a year or two ago and figured this is what it was. sure enough never happened again.
 

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Think back . . .

I also think it was a tube pinched under the tire bead or folded back onto itself in one place. Usually, such a pinched tube blow-out occurs after a flat repair or tube change. I'm guessing you did have to make a repair sometime before the blow-out.
 

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Side wall # is max pressure not recomended pressure. you only need ~~100 rear & 90-95 Ft.

Look up this subject in the archives. You are riding on way too much pressure and that WILL increase your probability of a blow-out. Give your tires some flex & let them do their job.
 

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Cat 6 rider
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Discussion Starter · #6 ·
HAL9000 said:
Side wall # is max pressure not recomended pressure. you only need ~~100 rear & 90-95 Ft.

Look up this subject in the archives. You are riding on way too much pressure and that WILL increase your probability of a blow-out. Give your tires some flex & let them do their job.
Not that I always do everything tires say, but they are quite specific- recommended minimum pressure is 115, maximum is 125.
 

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Discussion Starter · #7 ·
wim said:
I also think it was a tube pinched under the tire bead or folded back onto itself in one place. Usually, such a pinched tube blow-out occurs after a flat repair or tube change. I'm guessing you did have to make a repair sometime before the blow-out.
Had to change a tube on a ride about a week before- 75 miles or so before (it was a patched tube that already had several hundred miles on it. When I had to patch it I didn't bother putting it back in. I just put it in the aero bag as a spare.) Come to think of it, had a bear of a time getting it to seat, so maybe that's it- never had so much trouble changing a tube. It twisted one way, then the other, then back the first way. I thought I had it sorted so I wasn't thinking along those lines. I'm sure it wasn't pinched under the rim, but maybe there was a kink in it somewhere. Thanks. :thumbsup:
 

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I've done pretty well with this 2-part regimen:

1. Before stuffing the tube back into the tire, I inflate it to where it just begins to round itself out. That's very little pressure—just a few pounds. Once that barely inflated tube rest evenly inside the tire, I let most of the air back out to make tire seating easier.

2. After I get the tire seated properly but think that there still might be a kink in the tube, I pump to about 20 psi. Then I disconnect the pump and let all the air back out (very difficult to do on a group ride with everyone looking at you :D ) Then I pump to full pressure. In my experience, letting the air back out of a slightly pumped-up kinked tube straightens it out it every time.

Talcum ("baby") powder on your tube and/or in your tire reduces rubber-to-rubber friction a lot, allowing kinks to straighten themselves out easily. I keep my spare tube in a heavily powdered ziploc bag.
 

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dont take it so strict

California L33 said:
Not that I always do everything tires say, but they are quite specific- recommended minimum pressure is 115, maximum is 125.
the sidewal 115 psi min pressure is meant for those who weigh ~180-200+ pounds. If you are under ~180# then ~100psi (give or take 5 psi) *maximum* that you need for fitness or commuter riding, assuming modern 700*23C folding road tyre such as what you have now.

I have done a test doing the same course on 100psi and 110psi in dry weather a couple of times and I noticed no difference in my performance but comfort at 110 psi was noticably reduced. I weighed 150# at that time. I don't go above ~100 psi now but I do not race either.
 

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Tire casing have any damage? I caught my front tire once unseating itself off the rim... tube almost blew out the side... upon further inspection turns out that the sidewall had one of those ominous bulges
 

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i've found that there are significant variances in "ideal" pressures, even between clincher tires of the same size. i used to use GP3000s, and i would run them at about 95fr/110rr just to make them feel as if they were "gripping" the road in hard corners. any harder, and they felt like they were slipping. now i'm using TriComps, and i run 120fr/120rr, and instead of thinking "come on! hang in there!" in hard corners, i'm now thinking "i don't deserve to be upright, but somehow i am. cool!"

experiment with different tires- they all "like" different pressures! oh, and stay away from Specialized tires....they're super-durable, but they don't handle great.
 

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Blew one today myself.........

In my case, I had transferred components from my Trek 1200 to a new Soma frame and did not change the brakes to full fledged 'Long Reach' brakes. The tire must have squished just enough to rub the brake pad as I braked and BOOOOM. Scared me to death. The reason I drew this conclusion is that there was a new scuff mark all the way around the tire just above the rim......with a two inch gash.

The point to all this is.........have your brake pads moved to the point that they contact the tire instead of the rim?
 

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After installation, put 20 psi in. Inspect the bead by pushing the tire over all the way around and on both sides, inspecting the bead, to make sure you don't see the tube. If you see the tube, you may be able to wiggle it back in, or redo the install.

Pump them up to 140 psi overnight and let them sit. If it is going to blow, it will blow now (better now than on a descent).

Reduce to your riding pressure afterwards.
 
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