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  1. #1
    Afric Pepperbird
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    Replace tire if knob shears right off?

    I usually know when to replace my tires. Just yesterday, I noticed one of the knobs was completely shorn off of my rear tire (the brand and style shall remain nameless for now). This tire is just starting its second season of use.

    I know knobs shearing off is not that uncommon, but this is the first time it's happened to me. The knob disappeared, and there is a small, square patch where casing seems visible. I am concerned about that spot, since I run tubeless.

    Is this a huge concern while running tubeless? Or shall I just bite the bullet and get a new rear tire?

    Thanks

  2. #2
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    If your casing is exposed on the tire's tread, it's done. If the tire holds air, carry a tube and a boot, and ride on, but think about replacing it. If it's just the knob missing, and there is some rubber protecting the carcass, ride on.

  3. #3
    Afric Pepperbird
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    Thanks, I've decided to replace them.

    Bontrager XR4 Team, here I come!! I've heard nothing but great things about them (the latest models, at least, from 2012 onwards).

  4. #4
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    Quote Originally Posted by dirt farmer View Post
    I usually know when to replace my tires. Just yesterday, I noticed one of the knobs was completely shorn off of my rear tire (the brand and style shall remain nameless for now). This tire is just starting its second season of use.

    I know knobs shearing off is not that uncommon, but this is the first time it's happened to me. The knob disappeared, and there is a small, square patch where casing seems visible. I am concerned about that spot, since I run tubeless.

    Is this a huge concern while running tubeless? Or shall I just bite the bullet and get a new rear tire?

    Thanks
    Don't just replace it. Get the manufacturer to replace it. Not an acceptable mode of failure, imo.
    Tire Design & Development Engineer. The opinions expressed in this forum are solely my own.

  5. #5
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    Bryan, I respect your opinion a lot, but sometimes if you chose the wrong tyre, for he wrong terrain, this can happen. Case in point, chose a super tacky/soft compound tyre and take it on sharp coralstone rocks and you know it won't last, knobs will get ripped off and its not the tyres fault, it wasn't designed to handle that sort of terrain and abuse. So far I've had good luck with most all the tyres I've used to have this happen down on our coralstone, but then again I don't run super soft/sticky tyres and most have either small, short knobs or taller, bigger ones.
    Quote Originally Posted by bholwell View Post
    Don't just replace it. Get the manufacturer to replace it. Not an acceptable mode of failure, imo.
    One day your life will flash before your eyes, will it be worth watching??
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  6. #6
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    Quote Originally Posted by LyNx View Post
    Bryan, I respect your opinion a lot, but sometimes if you chose the wrong tyre, for he wrong terrain, this can happen. Case in point, chose a super tacky/soft compound tyre and take it on sharp coralstone rocks and you know it won't last, knobs will get ripped off and its not the tyres fault, it wasn't designed to handle that sort of terrain and abuse. So far I've had good luck with most all the tyres I've used to have this happen down on our coralstone, but then again I don't run super soft/sticky tyres and most have either small, short knobs or taller, bigger ones.
    No, knobs separating completely from the casing is not an acceptable form of failure, no matter the conditions. Choosing the wrong tire for the application can lead to accelerated tread wear, even some chunking (cut / chip), but it should not lead to knobs tearing off. I have seen this type of failure many times, and 99% of the time the undertread is way too thin, leading to poorly supported knobs. Another cause can be a poor compound mix, leading to reduced tread-to-casing adhesion. Replace tire if knob shears right off?-knob-tear.jpg
    Tire Design & Development Engineer. The opinions expressed in this forum are solely my own.

  7. #7
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    Sorry B, wasn't talking that sort of shearing off, meant shearing off so there's still rubber underneath hiding the casing, as in too soft a compound easily shredded by the rocks.

    Quote Originally Posted by bholwell View Post
    No, knobs separating completely from the casing is not an acceptable form of failure, no matter the conditions. Choosing the wrong tire for the application can lead to accelerated tread wear, even some chunking (cut / chip), but it should not lead to knobs tearing off. I have seen this type of failure many times, and 99% of the time the undertread is way too thin, leading to poorly supported knobs. Another cause can be a poor compound mix, leading to reduced tread-to-casing adhesion. Click image for larger version. 

Name:	Knob tear.jpg 
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ID:	793184
    One day your life will flash before your eyes, will it be worth watching??
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  8. #8
    Afric Pepperbird
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    Quote Originally Posted by bholwell View Post
    No, knobs separating completely from the casing is not an acceptable form of failure, no matter the conditions. Choosing the wrong tire for the application can lead to accelerated tread wear, even some chunking (cut / chip), but it should not lead to knobs tearing off. I have seen this type of failure many times, and 99% of the time the undertread is way too thin, leading to poorly supported knobs. Another cause can be a poor compound mix, leading to reduced tread-to-casing adhesion. Click image for larger version. 

Name:	Knob tear.jpg 
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ID:	793184
    Wow, your tire looks just like the one I mentioned - even down to the name that is visible

    Again, no worry though as I just bought those Bontrager's mentioned above. They get rave reviews for the conditions here in Bend, Or.

  9. #9
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    I think you'll like those XR4s if I have read right about your trails. Guys down here rides them and he says they have superb grip, although he got the 2.4"s first and they were huge, switched to the 2.2" and is now a happy camper with the trade off of rolling resistance vs grip for the amount of road we have to do to get to and between the trails.
    Quote Originally Posted by dirt farmer View Post
    Wow, your tire looks just like the one I mentioned - even down to the name that is visible

    Again, no worry though as I just bought those Bontrager's mentioned above. They get rave reviews for the conditions here in Bend, Or.
    Last edited by LyNx; 04-24-2013 at 04:20 AM. Reason: spelling
    One day your life will flash before your eyes, will it be worth watching??
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