What Caused My Blown Tyre?

[Graelwyn]

Been cycling for about 8 months now, and ride a carrera crossfire. Yesterday, I dropped into Halfords (from where I got the bike) to have my tyres topped up and picked up an adaptor so my old pump would work and headed for the main road, which had been newly done the evening before, I believe, with tarmac but was open to traffic as usual. Suddenly my bike felt like it had hit a massive bump, there was a loud bang and I flew over the handlebars and the bike landed on top of me.

The two men who came to help said it was the tarmac and it must have been hot still, while my boyfriend says they over inflated the tyres at the shop. Either way, I am somewhat nervous now and want to avoid this happening again, if possible as I tend to cycle along busy roads some of the time, including the one yesterday. I had never had this happen before, not even had a puncture in the less than 3 months I have had the bike, so am looking for advice on what most likely caused this and how to avoid falling off if it happens again on a road.

Thanks.

 

[dhk2]

It's likely that the tires were inflated to max pressure or beyond, and then the hot tarmac caused the temp/pressure to rise to the point the tire bead blew off the rim. I used to hear the same bang routinely back in the 90's at the start of crit races, when everyone thought they would be faster on over-inflated tires.

To prevent in future, don't inflate your tires to the max rating on the sidewall. Depending on your weight and the size of your tires, you'll likely find running 10-30 psi under that max rating is best. As you painfully found out, the front tire is critical to your safety. Since it carries less weight than the rear, suggest you may want to run it about 10 psi lower than what's best on the rear. Some tires shown a pressure range on the sidewall (eg, 6-8 bar or 87-116 psi) rather than just a max rating; wish they all did that.

Get your own pump for home and experiment it with the right pressures. At the correct pressure, the bike will grip the road better, ride and handle better, you'll have fewer punctures and flats, and lose virtually nothing in speed. Sorry about the bad luck you had.

 

[maydog]

Tires have to be highly overinflated to blow off the rim. I am larger than the average rider and typically have my rear tire inflated beyond its rated limit.

Its hard to say what caused the blowout without seeing the tire and tube - do have pictures. Likely the bead did come off, but it could have been mounted improperly or the bead itself was defective.

 

[dhk2]

Originally Posted by maydog .

Tires have to be highly overinflated to blow off the rim. I am larger than the average rider and typically have my rear tire inflated beyond its rated limit.

Its hard to say what caused the blowout without seeing the tire and tube - do have pictures. Likely the bead did come off, but it could have been mounted improperly or the bead itself was defective.

my theory is that when a tire goes bang from overinflation, it's because the bead pulls off the rim slightly in one place, enough to allow the tube to fail and go bang. Hey, I could be all wrong here...it's just a theory Suppose the tube could just fail from overinflation without the tire stretching or coming undone, but that's hard for me to visualize.

I left my bike lying out in the sun on a lunch break a long time ago and experienced a failure; it's also back when I ran max-or-over the rated tire pressure. Honestly don't recall what the tube looked like then; just that I changed it out in the middle of a field on a sunny, hot day.

Agree about the possibility of the tire not being mounted properly, or the bead not being the best. I've had some tires that just didn't seat well on the rim, requiring several attempts to get them mounted evenly. And of course clincher rims have pressure limits, since at some inflation point, the rim sidewalls will yield enough to release the bead. When I checked a Mavic rim a while back, the spec limit was 140 psi. Heavy wear on the braking surface would lower that limit I believe.

 

[Graelwyn]

Hi and thanks for the responses. The tyre was definitely hard as concrete when the store worker had inflated it, but when I returned after my accident they claimed they only put in the ammount of pressure the tyre is meant to take. I doubt my own weight was a factor as I am 126 Ibs. What I did notice is that the tyres themselves are very large in comparison to the rims.

 

[alienator]

my theory is that when a tire goes bang from overinflation, it's because the bead pulls off the rim slightly in one place, enough to allow the tube to fail and go bang.  Hey, I could be all wrong here...it's just a theory    Suppose the tube could just fail from overinflation without the tire stretching or coming undone, but that's hard for me to visualize. 
 
I left my bike lying out in the sun on a lunch break a long time ago and experienced a failure; it's also back when I ran max-or-over the rated tire pressure.  Honestly don't recall what the tube looked like then; just that I changed it out in the middle of a field on a sunny, hot day.    
 
Agree about the possibility of the tire not being mounted properly, or the bead not being the best.  I've had some tires that just didn't seat well on the rim, requiring several attempts to get them mounted evenly.  And of course clincher rims have pressure limits, since at some inflation point, the rim sidewalls will yield enough to release the bead.  When I checked a Mavic rim a while back, the spec limit was 140 psi.  Heavy wear on the braking surface would lower that limit I believe. 
 

You have to remember that change in pressure varies linearly with change in temperature, BUT the calculations are done in Kelvin or Rankin, depending on which Gas Constant you use. Either way changes in Fahrenheit are small changes in Kelvin. For instance a change from 80°F to 160°F is a 200% change in °F but is only a 14.8% change in K (299.8K to 344.3K), which would only cause a 14.8% change in pressure which would likely not exceed the blowout pressure. I think it's more likely it was combination of over inflation and either bad tire seating or pinched tube. It's also possible the rim could be defective.

 

[dhk2]

Originally Posted by Graelwyn .

Hi and thanks for the responses. The tyre was definitely hard as concrete when the store worker had inflated it, but when I returned after my accident they claimed they only put in the ammount of pressure the tyre is meant to take. I doubt my own weight was a factor as I am 126 Ibs. What I did notice is that the tyres themselves are very large in comparison to the rims.

Halford's webpage shows the Crossfire 1 and 2 models have 700x45c Kenda "multiuse" tires. I'm not familar with hybrid or MTB tires, but my guess is the max pressure rating on the sidewall doesn't exceed 85 psi. At your weight, would think 60 psi front and rear would be plenty. For a softer ride and better grip, 50 psi should do fine as well.

If you ride only on pavement and want easier pedaling or more speed, the ticket would be thinner tires with less blocky tread, or no tread (slicks). Depending on your wheel rim width, you might go down to a 700 x 32 tire.

 

[kdelong]

My guess would be the pinched tube. I have had a couple over the years. It has happened more often with a newly installed tire than when I just inflated a tire that has been on the bike for awhile. But I get the tire nicely inflated and installed back on the bike. I put the bike in the garage ready for a ride the next day. Anywhere from a couple of minutes to several hours later, there is a big bang from the garage like a fire cracker went off. When I go down to check, there is the tire flatted and sometimes blown right off the rim. This has happened with skinny road tires and MTB tires, neither one is immune to it.

 

[alienator]

My guess would be the pinched tube. I have had a couple over the years. It has happened more often with a newly installed tire than when I just inflated a tire that has been on the bike for awhile. But I get the tire nicely inflated and installed back on the bike. I put the bike in the garage ready for a ride the next day. Anywhere from a couple of minutes to several hours later, there is a big bang from the garage like a fire cracker went off. When I go down to check, there is the tire flatted and sometimes blown right off the rim. This has happened with skinny road tires and MTB tires, neither one is immune to it.

Ah the benefit of tubeless and tubular tires: no pinch flats.

 

[kdelong]

Originally Posted by alienator .


Ah the benefit of tubeless and tubular tires: no pinch flats.

The down side of a tubular is accidentally puncturing the tube while sewing up the casing. They should make them with zippers.

 

[swampy1970]

My guess would be the pinched tube. I have had a couple over the years. It has happened more often with a newly installed tire than when I just inflated a tire that has been on the bike for awhile. But I get the tire nicely inflated and installed back on the bike. I put the bike in the garage ready for a ride the next day. Anywhere from a couple of minutes to several hours later, there is a big bang from the garage like a fire cracker went off. When I go down to check, there is the tire flatted and sometimes blown right off the rim. This has happened with skinny road tires and MTB tires, neither one is immune to it.

In almost two decades of cycling I've never had that happen. Sounds "interesting." A friend had something similar happen and he remembered he just changed to rim tape and it was a bit too wide thus prevented the tire from seating properly.

 

[alienator]

The down side of a tubular is accidentally puncturing the tube while sewing up the casing. They should make them with zippers.
 

You have to schedule tubular repair time for those times when your chi is really bright. Tubular repair can be kind of a zen thing, but the zen bits can completely evaporate in a very short time. Tubular repair is also great exercise for thumbs.

 

[alienator]

In almost two decades of cycling I've never had that happen. Sounds "interesting." A friend had something similar happen and he remembered he just changed to rim tape and it was a bit too wide thus prevented the tire from seating properly.

I think there are far fewer bad tire seating issues these days, what with better tire and rim manufacturing with tighter tolerances. If someone wants to insure they don't have an issue with bad tire seating or tires otherwise blowing out, they only need to use Michelin tires with Campy rims. They might, if relatively unskilled, tear a number of tubes during installation and possibly throw things through either a TV or a picture window, but that Michelin won't come off the Campy rim. I think more often than not "blow outs" are the result of either poor tire installation technique, impatience, or both. On the Michelin front, I've put 1000 miles plus a bit more on some PR3's, and I have to say I'm damned impressed with the way they've been holding up in Tucson "tire challenging" environment. They've very few cuts and have had no punctures, despite all the broken glass I've been surprised by and the goat heads lying in wait.

 

[CAMPYBOB]

... and headed for the main road, which had been newly done the evening before, I believe, with tarmac but was open to traffic as usual.

Ashpalt is typically transported and applied at about 300-350° F.

Unless you hit freshly applied/rolled (not overnight cured/cooled) pavement on a sunny 100° F day and rode for miles on it...I doubt that was your issue.

More likely the blowout was caused by over-inflation or a defective/damaged by impact/sidewall cut tire (or you just popped the bead due to over-pressure?).



Tubular repair is also great exercise for thumbs.

The ability to swear in three languages is also a requisite skill.