Dings and cracks in carbon rims- Mtbr.com
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  1. #1
    rth009
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    Dings and cracks in carbon rims

    I hit a rock at speed the other day with the rear tire on my 29+ hard tail resulting in a burp and a good shot to the rim, which in turn resulted in the ding/crack in the pics below. It aired back up fine with my frame pump and I've ridden it on 2-3 rides over last 10 days with no issues.

    Should I be concerned if I keep an eye on it and it does not get worse? Is there anything I can do to repair it or keep it from getting worse?

    If this is not okay to ride than you can count me out for further carbon rims as this rim strike was no worse than I've done many times with quality aluminum rims. The rims at issue are 50mm rims running a 29x 3" tires.


    Dings and cracks in carbon rims-image.jpgDings and cracks in carbon rims-image.jpgDings and cracks in carbon rims-image.jpg
    Attached Thumbnails Attached Thumbnails Dings and cracks in carbon rims-image.jpg  


  2. #2
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    Personally, I'd glue it with some thin CA and then keep an eye on it.

  3. #3
    rth009
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    By CA, you must mean superglue?

  4. #4
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    Quote Originally Posted by Lone Rager View Post
    Personally, I'd glue it with some thin CA and then keep an eye on it.
    ^^this
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  5. #5
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    What does it look like on the inside?

    There appear to be stress marks below the crack, and the crack looks like it will get significantly worse, if not fail completely, if it takes another hit in the same place.

    I had a really similar crack in my Light Bicycle rim a month ago. It held air for a little while, but would lose 50% of it's pressure overnight. The rim was in pretty rough shape all around, so I just replaced it. I didn't want it to fail completely out on the trail.

  6. #6
    rth009
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    I haven't taken the tire off to look inside yet, but I will when I do the superglue repair. It actually looks worse in the pictures than it does in real life.

    I also note that this particular rim is actually a warranty replacement that was replaced for a different reason, but when I took off the prior rim I noticed several cracks I hadn't noticed before.

    My thought is, rim strikes happen, especially when you ride hard tails aggressively and if carbon rims can't take moderate strikes without coming apart, what good are they? Admittedly, these are not Enve rims. Can a name brand carbon rim take a solid rim shot without cracking?

    Thanks for the responses.

  7. #7
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    Nevermind. I missed the "plus" part.

    There's so many factors at play. But to answer the "what good are they" question, I have light bikes rims that have taken dozens of hard hits. They're going on 3 years old. I'm not interested in building wheels with alloy rims any more. As long as there are reasonably priced options, I'm not switching back. Carbon rims are just so much easier to work with.

  8. #8
    rth009
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    These are 50 mm rims with Vitoria bomboloni 29 x 3" tires.

  9. #9
    mtbpete
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    If the tire burped air that seems like a pretty big hit. What brand of rim is this? Did your other aluminum rims burp when you hit them with the same force?

  10. #10
    rth009
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    Actually, I cannot confirm a burp as a result of this hit, but I know I lost some pressure and had to air it back up with my frame pump, which I did easily and it has held air no problem since then. there was no sealant stain near this crack/ding that I could see.

    It is a nextie jungle fox (29" x 50mm width) , second generation.

    I've hit just as hard with aluminum rims and sometimes it Would snake bite the tire, which might or might not seal with sealant, but the rim was fine.
    Last edited by rth009; 05-15-2016 at 10:48 AM. Reason: got rim name wrong

  11. #11
    mtbpete
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    Last year a customer of mine ordered a Nextie Snow dragon rim that cracked very easily. It couldn't even hold spoke tension. They replaced it with a Wild dragon that seemed much better. I doesn't look like they make the wild dragon in 50mm?

    What brand of aluminum rims did you have? Most of the lightweight and medium weight aluminum rims will bend if they hit an object hard enough to cut a tire.

  12. #12
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    IMO, that's DONE! No way I'd trust that to rail down some chunky downhill run later on. Perhaps it's time to consider air pressure when riding in such conditions that bring on such significant hits. That was definitely a significant hit to do that damage.
    Last edited by Oh My Sack!; 05-13-2016 at 08:21 PM.

  13. #13
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    I agree. No way would I ride that anywhere except back to the car.

  14. #14
    rth009
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    Quote Originally Posted by changingleaf View Post

    What brand of aluminum rims did you have? Most of the lightweight and medium weight aluminum rims will bend if they hit an object hard enough to cut a tire.
    I have bashed a first generation Stan's Flow 29 numerous times harder than this with no issues

  15. #15
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    O.P. I rode a LB early production 29 rear rim with a crack all the way through and larger than that for about a year and a half. Put a little super glue on it after about a 8months for the heck of it. It finally delaminated to a point where the rear tire would no longer hold air, nothing catastrophic, no death, dismemberment or splosions. Mind you, I would have taken less chances if it were the front wheel. After I cut the hub out and rebuilt the wheels, I decided to do some stress testing on the bare rim with the crack in it. Holy shit these things are way way way stronger than any aluminum rim I have ever tested. Even with a 4" long delamination all the way through the sidewall of the rim. I'm talking all my strength to do minimal damage kinda stuff. Smacked it against the garage floor about 10 times as hard as I could. Stood the rim on edge, wrapped the crack with a rag and sat on it and bounced up and down on it. Nothing!

    On another set of wheels, with Nextie carbon rims, I flatted out the rear tire and slowly rode home about 2 miles downhill on the trail and another 1 mile on the road with the flat tire only protecting the rim lip. That wheel is still in perfect condition. This was definitely improper use of the product on my part.

    YMMV. If you're concerned, replace it. It's not worth getting hurt because of the probably minimal chance of failure or the lack of confidence in your gear.
    Last edited by oaklandish; 05-14-2016 at 09:14 PM. Reason: misspelled splosions

  16. #16
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    Don't use super glue!

    Use epoxy resin, the two part stuff you mix up. Be careful do it slowly and make sure you get the amount to mix so that makes a strong bond.

    Get some electrical tape, a piece of wood the right size to make a press against the rim so you can get the rim back to the same place where it was before the crack occurred and use a g-clamp.

    put a small amount of resin into the affected area and cover with electrical tape' then cover with the wood press and clamp and leave it over night.

    Basically the exact same thing happened to me last week going down hill about 40mph in the UK, got to the bottom and heard a loud ping sound and all the tyre pressure deflated completely from the front wheel. Then I rolled about 20-30 metres to controlled stop but damaged the rim. I think this was a combination of factors, pressure too low on front tyre and possibly rim not wide enough (24mm OD) with a 2.25 tyre.

    A friend of mine runs carbon rims too and he said the tyre has a tendency to roll off the rim more than alloy because it's so stiff.

    the repair advice above was given to me last Monday after my ding by a carbon fibre cycle repair specialist in the UK. he gets all sorts of wheels in all the time and was currently repairing a set of ENVE down hill carbon rims.
    Attached Thumbnails Attached Thumbnails Dings and cracks in carbon rims-image.jpg  

    Dings and cracks in carbon rims-image.jpg  

    Dings and cracks in carbon rims-image.jpg  


  17. #17
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    Just wanted to add that I put a new tyre on the wheel and it was losing air, couldn't get it to seal up. So I run it with a tube and hammered the bike around a local trail and the wheel is no different after a good hammering, so I'm going to do the same repair mentioned above soon and then rim should be as good as new.

    This seems to be a big disadvantage of using carbon fibre even if you spend mega money on the top brands, the same thing will happen. It's the inherent nature of composite material, I too have run crest alloy rims for years and never suffered this problem. Seems to me alloy rims last longer than carbon, but carbon build a much stiffer and lighter wheel since its stronger but when it takes any kind of impact then it seems to break.

  18. #18
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    My experience has been the opposite, carbon has been more durable for me. They've taken hits that would have bent alloy rims beyond repair for me. Everything breaks eventually, I'm very happy with the durability of my Light Bicycle rims.

    Maybe your just not running enough pressure?

  19. #19
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    I went to the damage zone this morning to inspect the area where my rim went, there was a half brick just on the bottom of the slope, looked like it had been sharpened and deliberately left there by some malicious person. Also inspected my tyre and there is a 15mm rip through one of the knobs, which has gone right through the tyre.

    I have no dougbt that this has caused the damage and I'm actaully impressed how well the wheel has survived such an heavy impact into a large sharp object.

  20. #20
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    Quote Originally Posted by Flucod View Post
    First of all, if you have have rim strikes, your pressure is wrong. In 30 years of riding I have had one rim strike. You have had numerous with every wheel you have owned by the sounds of it. Second, carbon is not the choice for you, it is stronger and stiffer in its application, but there is not any carbon wheel made that will hold up to a rim strike. You scare me, lol.
    As stated above, a very sharp brick ripped the tyre and struck the rim. Only realised exactly what happened this morning by inspecting all the factors. I did think initially that the pressure was wrong but now I wouldn't be surprised if it had gone the same way with more pressure given the circumstances.

  21. #21
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    Quote Originally Posted by Flucod View Post
    ... In 30 years of riding I have had one rim strike...
    Your pressure is too high.

  22. #22
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    Quote Originally Posted by Lone Rager View Post
    Your pressure is too high.
    I was going to say the same thing, for me it's kind of a balancing act and if I used high enough pressure to prevent ever having a rim strike it would rather suck for the rest of the ride.

  23. #23
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    Good advice about the resin. I'll try that next time.

    Pressure is key. If you ride "heavy", even if you are light you might need a little more PSI to protect the rim. I ride with about 22-24PSI on my rear and my riding weight must be around 185 lbs, but I ride "light", using my legs as much as possible to absorb the chatter. On a parallel tangent I was trying flat pedals for about a month and a half and noticed that it is much harder to ride "light" on the rear wheel because you have to keep your heels down to keep the weight on the pedals. I since switched back for various reasons but I definitely felt that rim strikes were going to be a lot more common for me riding flats.

  24. #24
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    Oaklandish, yeah I'm a very similar rider to you. I'm about 180lbs so a little lighter :-) and I run about 22-28psi in the rear dependant on environment, less pressure for trail use and more for general long sections of off road. Front pressure about 18-23psi and the bike is 19.14lb in weight using egg beaters. I have only had my 29er for a few months and finding I may need a bit more pressure than the 27.5 bike due to bigger wheels, I'm still experimenting a lot with this bike actaully, gearing and tyre pressures and changing stem sizes.

    After my carbon rim ding, I was really thinking about getting new wheels built with alloy rims but now after the complete evaluation, I think I'm going to stick with carbon rims.

    Rth009, I don't think your damage is that bad anyhow. I think you can do the repair to that rim and it will be good to go and probably last for years.

    The carbon fibre repair specialists I spoke too said there is loads of good carbon repair know how on YouTube if you really fancy having a go yourself. Good luck :-D

  25. #25
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    With each picture the damage looks worse than the one before. I wouldn't chance riding on that rim except JRA pace back to the car.

  26. #26
    rth009
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    I took the tire off and took pics

    Dings and cracks in carbon rims-image.jpg

    Dings and cracks in carbon rims-image.jpg

    Dings and cracks in carbon rims-image.jpg


    I've ridden it a time or two since my original post. It looks the same as far as I can tell.


    As far as a repair, I haven't used epoxy much. Will I be able to get epoxy in this tiny crack or should I use the following loctite thin super glue It's not "CA" but it says it's thin.

    Dings and cracks in carbon rims-image.jpg

  27. #27
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    I wouldn't use superglue, may be ok but chemicals could react with the original epoxy resin it was made with, I don't know enough about it to be honest but if a specialist says to use expoxy then it's probably best to use epoxy resin and makes sense considering that's what bonded the carbon fibre together from the manufacturer when it was originally made.

    That wheel looks absolutely fine, I think my damaged rim has taken a bigger hit than that and I have ridden the bike about 12 times since and ridden it hard with a tube in and it hasn't showed any worse signs. Damage still looks the same.

    I will be using expoxy resin to repair my wheel but I haven't had the time to get around to it yet and I also wanted to see how strong the wheel still is before doing it. Impressively strong.

    the expoxy resin should be cheap enough, comes in 2 tubes. I was told not to use the polyester type as its not as strong. Then you just mix the recommended amount together and use it quickly as it sets fast. Best to do it early in the morning or later in the evening so it doesn't go off too quickly.

    i would use a g-clamp too with a piece of wood to pull the rim in a bit so it should set straight. Put the resin in first and then carefully use the clamp and leave it over night.

  28. #28
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    That Loctite is CA. Thin is good as it will wick into the crack. CA will not adversely react with epoxy. Epoxy is tougher and could be a better repair if gotten into the crack. Starting with thin long cure resin will help, and the application of heat with a hair drier will make it much thinner. Warm the rim before application, apply some resin, then warm further with a hair drier. Don't get it too warm. Practice first. I use 635 with medium hardener from US Composites.

    Edit: I should mention that goal of using the hair drier is only to get it thin out and flow, not to get it to cure too quickly. The heat is applied to the epoxy only for maybe 5-10 seconds.
    Last edited by Lone Rager; 05-23-2016 at 04:29 AM.

  29. #29
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    Good job!

    Nice tips Lone Rager

  30. #30
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    The best thing with carbon rims is that they never become warped or get flat spots. The cracks that you get from time to time can be easily repaired with epoxy resin and a little carbon or fiberglass. This kind of repair takes about 1 hour and will be just as strong as before.
    A aluminum rim had ended up in the trash after my last treatment!
    Attached Thumbnails Attached Thumbnails Dings and cracks in carbon rims-20160515_201134.jpg  


  31. #31
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    Anyone care to comment on this one? My back wheel slid into a rock after landing a small drop into a chunky section. I wasn't going that fast, but the force on the wheel was reasonably large since it trapped the wheel momentarily and shaved off a lot of my momentum. A small flake came off when I was inspecting the damage. I assume that this is the cosmetic layer? I emailed these pictures and description of the event to a couple of local composites companies and both seemed confident in their ability to repair it (cost $75-$100). I'm wondering if I need a professional repair or if I can cover it in epoxy myself and call it good.
    Attached Thumbnails Attached Thumbnails Dings and cracks in carbon rims-file-jun-01-12-02-07-pm.jpg  

    Dings and cracks in carbon rims-file-jun-01-12-00-58-pm.jpg  


  32. #32
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    That looks more than cosmetic to me. Hard to tell for sure in a picture though.

  33. #33
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    Drybear, I'm interested in your fix. I have a few questions:
    - Do you have a before picture? I'm curious to see what kind of damage you are fixing.
    - How many layers of carbon did you use?
    - Can you provide an specifics on the carbon and resin you used and where you purchased them?
    - How many fixes like this have you done? Did you learn anything important that I should consider before attempting it myself?

  34. #34
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    Dings and cracks in carbon rims-20160508_192919.jpgDings and cracks in carbon rims-20160508_192946.jpg
    Quote Originally Posted by Jim-CO View Post
    Drybear, I'm interested in your fix. I have a few questions:
    - Do you have a before picture? I'm curious to see what kind of damage you are fixing.
    - How many layers of carbon did you use?
    - Can you provide an specifics on the carbon and resin you used and where you purchased them?
    - How many fixes like this have you done? Did you learn anything important that I should consider before attempting it myself?
    Hi, here are a few before Pictures.
    I used three layers of carbon fibre but it was a bit to much.
    I recommend you to sand down the surface properly so that the new carbon layers dont build up too much and try to find as thin (light) carbon fiber as possible. You can find epoxy resin in most surf shops, they often have dingfix kits that includes all you need. All epoxy has very good adhesion so for this kind of small repair, they will all be good enough.
    Good luck!

  35. #35
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    To everyone attempting repairs yourself, please use protection, i.e. nitrile gloves, safety glasses and a respirator, especially when sanding. You really don't want resin on your skin and carbon fiber gets itchy too.
    n+1

  36. #36
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    Dinged my wheel...do you think I need it replaced or can I do the epoxy/resin thing.

    Dings and cracks in carbon rims-2b8da495-b58e-4697-a282-b4e970e823b1.jpg

  37. #37
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    I just had my first crack in a carbon rim after about 6 years of no issues. Totally my fault. My wheel had dried sealant and my pressure dropped really low. Luckily the damage didn't extend into the rim bed. I cut off loose fragments, sanded, pushed epoxy into the wound (this alone made it rock solid again), added a small patch of carbon weave and more messy epoxy, sanded again, and covered with some clear coat. It looks awful up close, but I know how to do it better next time and you can't even see it now that I got the wheel dirty again. Overall, I'm glad I didn't rush to buy a new rim. This one has a long life left and is still perfectly straight.
    Dings and cracks in carbon rims-img_20200615_141959.jpg
    Dings and cracks in carbon rims-img_20200617_181458.jpg
    Dings and cracks in carbon rims-img_20200618_125049.jpg
    Dings and cracks in carbon rims-img_20200625_081955.jpg
    Dings and cracks in carbon rims-img_20200625_083546.jpg

  38. #38
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    I wouldn’t do better myself. I like the S2k in the background.

  39. #39
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    Quote Originally Posted by Le frog View Post
    I wouldn’t do better myself. I like the S2k in the background.
    We like her too. Her name is Lola. We got her in 2013

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