Heat Punctures

by Richthornton   July 11, 2014  

I'm having some real issues at the moment, and hope anybody can help to diagnose the problem. Apologies for what may turn out to be a lengthy background story!

So on 3 of my last 4 rides I have sustained a heat puncture. Never had one in years of riding and then 3 within a week. All have come on steep, tricky(ish) descents.
The first one was in the wet on a cool day, the second two on dry, warm days.
On each occasion the front rim has been incredibly hot, too hot to hold, so have had to wait a minute or two before beginning the repair - that hot!
After the first one, I noticed that the rim tape was a little skewed in places, some of the spoke holes were just showing. I figured that that was the problem. It was nylon-type rim tape, quite stiff, and out on the road I wasn't able to do anything with it so I put a new tube on and hoped for the best. It got me round a further 50 miles and then I guess I thought it would be fine.
Since then I started using the rear brake a lot more, to share the load, allow the front to cool a bit more, but I've locked up the rear at least once as a result and have lost lots of confidence on descents, I don't trust either brake anymore.
After the second one, when I got home I removed the rim tape, and not having any to replace it with, used 2 layers of electrical tape. I know this isn't exactly recommended but it's what I did. Electrical tape or not, it's the heat level of the rim that concerns me most.
Here's the facts:
Me : 15 stone ish, I take quite a lot of stopping on a steep descent, but I love climbing, and living in North Lancashire there's plenty of it, I have climbed and descended using the same equipment, or equivalent, for many years and this has never happened. Can anyone try to explain what might be causing it to happen all of a sudden?
Wheel: Pro-Lite Bracchiano
Tyre - Schwalbe Ultremo ZX,
Inner tubes - I have always bought the cheapest I can find
Brakes - Shimano 105, and I think the pads are 105 too.
All of this gear is in good condition but none of it is new, and I have descended plenty of hills using this stuff before.
Thoughts? experiences? where should I be looking to solve this?
Thanks in advance.

9 user comments

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Wow ! I have only heard of heat blow outs on long alpine descents before usually caused by feathering the brakes all the way down a long descent. Is this a factor that might be coming in to play ?
The other one is patched tyres (after a puncture) are known to be more vulnerable.
What brake pads are you using ? Are they not too worn out ?

posted by arfa [484 posts]
11th July 2014 - 22:46

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These are not long alpine descents, the longest of the 3 was about 3 miles, and today's was barely half a mile. Heavy use of the brakes due to twisty nature of the descents, but nothing I'd never done before and (particularly after the first incident) with a conscious effort to use the front brake as little as possible to avoid such an occurrence.
I would never patch a tyre except in an emergency, but if you mean patched tubes, I rarely patch these either, just buy cheap and replace for convenience.
The brake pads appear in good nick with plenty of wear left and no foreign bodies embedded.
My gut feeling is something up with the rim, or maybe the tyre is not providing enough grip, hence more breaking required to slow down?

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posted by Richthornton [99 posts]
11th July 2014 - 23:03

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How do the puncture holes look when you take the tubes out? Is it a small pin prick hole, a gash, does the tube look to have melted, are the puncture holes always in the same place? Did the punctures always occur whilst travelling downhill?

posted by Leeroy_Silk [45 posts]
12th July 2014 - 8:56

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I got two of these last summer whilst riding in the Vosges Mountains last summer. However the longest descent I did was about 8 miles and my Garmin read 40 degrees for air temp (it was stupidly hot last summer!). When I looked my rim tape had basically melted and pulled into the spoke holes. This had then sucked the inner tube in and given little pinch flats. I changed the rim tape and that was it sorted.

posted by Dutch25 [20 posts]
12th July 2014 - 10:04

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Leeroy_Silk wrote:
How do the puncture holes look when you take the tubes out? Is it a small pin prick hole, a gash, does the tube look to have melted, are the puncture holes always in the same place? Did the punctures always occur whilst travelling downhill?

The holes are a single small gash and the tube doesn't show any signs of melting. They have only occurred when travelling downhill (when breaking heavily).
I'm now considering, given what Dutch25 has said, that the spoke holes have been exposed, (they certainly were on the first 2 flats, and as I was using electrical tape when the third occurred....) and the tube sucked in, but I'm still concerned about the heat of the rim, maybe it's normal and not contributing to weakness in the tube at all, it's just that I've never felt the temp of a rim after a sustained period of breaking before.

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posted by Richthornton [99 posts]
12th July 2014 - 13:27

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I would be surprised if your problem stems from excess heat, I think it much more likely you have a fault in your wheel. The rim tape seems to be the prime suspect and I would junk the insulating tape and replace it with proper, fabric rim tape. I prefer it to the plastic type as it doesn't stiffen with age or deform into a twisted mess.

Wheel rims, and especially discs, do get extremely hot under prolonged braking. There's nothing new here and race mechanics commonly burn their fingers working on hot metal.

Best of luck.

Mike

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posted by mike the bike [128 posts]
12th July 2014 - 16:43

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Dutch25 wrote:
When I looked my rim tape had basically melted and pulled into the spoke holes. This had then sucked the inner tube in and given little pinch flats. I changed the rim tape and that was it sorted.

^^^ This.

Use Vellox tape (don't use plastic) and make sure those holes have good coverage or as soon as the tube heats up it will expand itself into those spoke pockets and tear.

"because a goal without a plan is just a wish"

posted by bikeyourbest [23 posts]
12th July 2014 - 17:45

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mike the bike wrote:
I would be surprised if your problem stems from excess heat, I think it much more likely you have a fault in your wheel. The rim tape seems to be the prime suspect and I would junk the insulating tape and replace it with proper, fabric rim tape. I prefer it to the plastic type as it doesn't stiffen with age or deform into a twisted mess.

Wheel rims, and especially discs, do get extremely hot under prolonged braking. There's nothing new here and race mechanics commonly burn their fingers working on hot metal.

Best of luck.

This is what I wanted to hear, thanks Mike.
Thanks everyone for your contributions, i'll get some decent rim tape ordered now. Smile

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posted by Richthornton [99 posts]
13th July 2014 - 9:25

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Possibly some more efficient break pads might help. The differences between something like a Swisstop set of pads and 105's are pretty sizeable..

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posted by DanTe [51 posts]
13th July 2014 - 22:40

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