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Suppose I wear a bicycle helmet, and I fall hard and my helmet cracks. Do I buy a new helmet or can I try repair the old one with some glue?

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Obviously per the responses below the helmet should be replaced immediately. However in an emergency situation (like on a tour and you are 100 miles from the nearest bike shop) some helmet is better than none, it should be replaced ASAP, but some glue can hold the tide for the (very) short term. –  crasic May 19 '11 at 22:18
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Very glad you asked. Please replace your helmet. We like you. If you glue it together... don't let its cosmetic appearance lull you into a false sense of security. –  DC_CARR May 20 '11 at 0:20
    
If you're particularly hard on your helmet it might be worth looking into a skateboard-style/bmx helmet. They're more durable than a foam bike helmet and mine took many hits before breaking. To my experience they're heavier and get hotter than foam helmets. –  krs1 Oct 18 '11 at 15:33
    
Possible duplicate: bicycles.stackexchange.com/questions/592/… –  amcnabb Jul 6 '12 at 17:12
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4 Answers 4

up vote 24 down vote accepted

They're designed to take the impact of the fall, once they've done the job they can't be used again and you must buy another. It's not safe to attempt to repair a helmet with glue.

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Absolutely correct. Bike helmets are good for one crash. Even if it doesn't have any visible damage to the helmet, if it takes a hit, you need to replace it. –  Apreche May 19 '11 at 12:46
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As I understand it, the energy of the fall is absorbed by permanently compressing the foam, so once that happens any subsequent fall will transmit that energy to your head. ow. –  James Bradbury Dec 16 '12 at 9:20
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Summary:

  • Did you crash it? Replace immediately.
  • Did you drop it hard enough to crack the foam? Replace.
  • Is it from the 1970's? Replace.
  • Is the outside just foam or cloth instead of plastic? Replace.
  • Does it lack a CPSC, ASTM or Snell sticker inside? Replace.
  • Can you not adjust it to fit correctly? Replace!!

    (source: Bicycle Helmet Safety Institute)

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Is the outside just foam or cloth instead of plastic? I tore the plastic veneer off my hardfoam helmet after going through some heavy brush on my MB - why does losing the decorative plastic necessitate replacing the helmet? –  crasic May 19 '11 at 22:17
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"If you have one of the 1980's all-foam helmets with perhaps a cloth cover, we would recommend replacing that one. Lab tests showed some years ago that bare foam doesn't skid well on pavement, and could jerk your neck in a crash. The cloth doesn't help much. In addition, some of them had no internal reinforcing, and they tend to break up in a crash. That's not serious if you just fall, but if you are hit by a car the helmet can fly apart in the initial contact and leave you bare-headed for the crack on the pavement." (same source) –  deizel May 20 '11 at 15:28
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Helmet manufacturers recommend replacing helmets after the crash, even if there are no visible cracks, just to be sure. If you see a crack, the helmet cannot do its purpose anymore. You might want to replace the helmet if it is getting old (a few years or so) even if there has been no crash.

Remember, most of us are making money with our brain, so we need to protect it.

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+1 brain -> money –  James Schek Jun 27 '11 at 3:29
    
Except for the helmet manufacturers, who are making money by selling us helmets, even if we have one. –  Mladen Jablanović Dec 16 '12 at 9:30
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@MladenJablanović -- There are a few manufacturers who will replace a helmet for free after it's been visibly damaged in a crash. –  Daniel R Hicks Dec 16 '12 at 13:24
    
Nice to know that. However, benefit of cycling helmets is generally dubious topic, and I would not rely on everything that helmet manufacturers claim. Also, saying that "if there is a crack, it cannot do its purpose anymore" is plain wrong. It can still save your life, although not with the same probability. But neither the completely new and sane helmet itself is a guarantee for that. –  Mladen Jablanović Dec 16 '12 at 19:22
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You should NEVER repair any bike helmet under any circumstances! The helmet manufacturers even recommend replacing a helmet after several years of use. ( Imagine that! ) I don't replace my helmet that often, but do inspect it for structural damage, which occurrs mostly with the styrofoam liner that begins deterorating after some days in the sun and sweat/oils from the skin. I guess we all have to ask ourselves...how much is my head worth if there's an accident? I doubt anyone thinks their head isn't at least worth the $50 to $100 price tag of a helmet every 5 or so years.

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Hmm, I've had mine 12 years without accident. I guess I should consider replacing it anyway. –  James Bradbury Dec 16 '12 at 9:29
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