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View Full Version : pinch flat vs tire coming off the rim?


etu
10-04-2014, 03:15 PM
early this week, i had a near miss coming down a hill at decent clip. just as i straightened out after the final curve, there was a big "bang" in the back with lots of wobbling and a sensation that i was definitely riding on the rims.
never had a pinch flat before, but as there were no bumps (smooth asphalt) and tires were at reasonable pressure (55psi for 42mm width), am i correct to assume that the tire just wasn't seated properly and blew off? tires were mounted months ago, so a little surprising if that is the case. when i did change the tube and remounted the tire, it went on almost too easily by hand. bad combo?

gomango
10-04-2014, 03:19 PM
early this week, i had a near miss coming down a hill at decent clip. just as i straightened out after the final curve, there was a big "bang" in the back with lots of wobbling and a sensation that i was definitely riding on the rims.
never had a pinch flat before, but as there were no bumps (smooth asphalt) and tires were at reasonable pressure (55psi for 42mm width), am i correct to assume that the tire just wasn't seated properly and blew off? tires were mounted months ago, so a little surprising if that is the case. when i did change the tube and remounted the tire, it went on almost too easily by hand. bad combo?

What tire/rim combo?

p nut
10-04-2014, 03:31 PM
Did you check the bead on the tire? I had a Continental with a bad bead with the exact same scenario.

I have tires that I can easily mount by hand, but have not had issues with, especially if I'm using a tube.

etu
10-04-2014, 04:12 PM
pacenti cl 25 and gran bois hetres (650bx42) - had the combo for over year with many happy miles both off road and on the road.

i will plan on examining the bead very carefully.

seanile
10-04-2014, 05:17 PM
how old is the rim? the braketrack could be worn and weak/flexible from braking.

palincss
10-04-2014, 09:52 PM
early this week, i had a near miss coming down a hill at decent clip. just as i straightened out after the final curve, there was a big "bang" in the back with lots of wobbling and a sensation that i was definitely riding on the rims.
never had a pinch flat before, but as there were no bumps (smooth asphalt) and tires were at reasonable pressure (55psi for 42mm width), am i correct to assume that the tire just wasn't seated properly and blew off? tires were mounted months ago, so a little surprising if that is the case. when i did change the tube and remounted the tire, it went on almost too easily by hand. bad combo?

If by "pinch flat" you mean the snakebite double-cut flat tire you get when you bottom the tire out against the rim when hitting a pothole or the transition edge from milled to unmilled pavement, they never give you a big BANG.

Some people erroneously call the blow-off you get when you've improperly installed the tire and have caught the tube under the tire bead a "pinch flat." That kind of flat definitely gives you a huge BANG.

etu
10-05-2014, 01:00 AM
If by "pinch flat" you mean the snakebite double-cut flat tire you get when you bottom the tire out against the rim when hitting a pothole or the transition edge from milled to unmilled pavement, they never give you a big BANG.

Some people erroneously call the blow-off you get when you've improperly installed the tire and have caught the tube under the tire bead a "pinch flat." That kind of flat definitely gives you a huge BANG.

What is odd is that the since I've last mounted the tires I've put at least several hundred miles on them. I don't recall ever completely deflating the tires either.
Wouldn't an incorrect installation have manifested itself a lot earlier?
Tire bead is fine, rim was disc specific and fine but now damaged at the valve stem hole, and the rim tape was correctly in place.
Would feel a lot better if I had a good explanation for this incident.

fogrider
10-05-2014, 03:25 AM
What is odd is that the since I've last mounted the tires I've put at least several hundred miles on them. I don't recall ever completely deflating the tires either.
Wouldn't an incorrect installation have manifested itself a lot earlier?
Tire bead is fine, rim was disc specific and fine but now damaged at the valve stem hole, and the rim tape was correctly in place.
Would feel a lot better if I had a good explanation for this incident.

if you only had about 55 psi in the tire, a tube caught in the mounting bead might not be very visible but if you bottomed out on it, the added pressure or deformation of the tire could allow the tube to blow out the side. after setting the innertube and pumping some air, you should always check both sides of the tire by squeezing the tire to see that the tube is not visible. I would say about 1 out of 10 times, you will see part of the inner tube pinched by the tire.

Steve in SLO
10-05-2014, 11:33 AM
Where was the big hole in the tube?
You might get some answers by placing the tube as it was mounted either next to the tire or in it and examining the area of the tire and rim around where the tear is. The valve stem hole sounds a little sketchy, as well.

rab
10-05-2014, 07:16 PM
Yes, very curious to know what the failure point on the tube looked like? Signs of wear, maybe as suggested pinched slightly in the bead and finally gave?

I have had one or two big bangs that I never could figure out...