Page 3 of 9 FirstFirst 12345 ... LastLast
Results 51 to 75 of 225
  1. #51
    RoadBikeReview Member
    Reputation:
    Join Date
    Oct 2013
    Posts
    932
    If the OP is groggy on exactly what happened, it could have been a flat on the front tire, that led to a rolled tire and sudden crash. It's happened to me, I went down while turning on a tire with a slow leak and almost no pressure left. The front end went out like I was on ice.

  2. #52
    RoadBikeReview Member
    Reputation: velodog's Avatar
    Join Date
    Sep 2007
    Posts
    7,139
    Quote Originally Posted by mik_git View Post
    looking at the upper part of the failure, the front of the fork looks like it's snapped, jagged, but clean, whereas the trailing edge of the fork looks like it been the end of the failure with stuff going everywhere and delamination up towards the crown. Like when it failed it failed backwards, folding under, like it hit something (and that something could be anything small or large) rather than just collapsing...
    also the front tyre looks like it has a big mark on it, but hard to tell from the pic.

    Are you seeing the mark at about 9 or 9:30 on that tire?
    Too old to ride plastic

  3. #53
    RoadBikeReview Member
    Reputation:
    Join Date
    Jul 2012
    Posts
    964
    Quote Originally Posted by velodog View Post
    Are you seeing the mark at about 9 or 9:30 on that tire?
    yeah, right at the leading edge where it's lying...

    also another ... something, maybe a cut...or nothing at all, at the top between the break in the fork and the bar, next to a white mark on the paver... could be nothing (both of them) or could be something telling
    All the gear and no idea

  4. #54
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by cxwrench View Post
    ^This^.

    You don't normally see both fork legs breaking in the same exact place/way w/o some kind of help. There's an industry term..."JRA", just riding along. It has been associated w/ issues like this forever. "I was just riding along and both fork legs exploded". Very rare for something like this to happen.
    If there is a design flaw, I don't see why the flaw wouldn't be symmetrical and cause the fork to fail symmetrically. I imagine one leg would start to fail first, but the other would fail as soon as all the load got shifted to it.

    No, I'm not saying that the fork is definitely at fault, but if if the "weak spot" is 5" down each fork leg, than that's where the fork will break, 1-2. Doesn't seem that much different than frame failures where the DT breaks followed immediately by the TT.


    This appears to be a stress point on carbon forks. This one is also supposed to be a real JRA.



    Similar:


    Not symmetrical, but similar failure point:



    It seems like most of the single sided failures are with disc brakes.
    Get a better saddle: www.kontactbike.com

  5. #55
    RoadBikeReview Member
    Reputation: 11spd's Avatar
    Join Date
    Sep 2015
    Posts
    1,796
    Quote Originally Posted by Kontact View Post
    If there is a design flaw, I don't see why the flaw wouldn't be symmetrical and cause the fork to fail symmetrically. I imagine one leg would start to fail first, but the other would fail as soon as all the load got shifted to it.

    No, I'm not saying that the fork is definitely at fault, but if if the "weak spot" is 5" down each fork leg, than that's where the fork will break, 1-2. Doesn't seem that much different than frame failures where the DT breaks followed immediately by the TT.


    This appears to be a stress point on carbon forks. This one is also supposed to be a real JRA.



    Similar:


    Not symmetrical, but similar failure point:



    It seems like most of the single sided failures are with disc brakes.
    In bold above, since you don't see it, I will explain why symmetric breaks if JRA, with even symmetric loading don't have to occur at all. Reason is...layup maybe precipitously weaker on one fork leg than the other...causing a single fork leg to fail, then the other. The load path on the second fork leg would be substantially different than the first leg because the first leg would have the support of the second.

    Also, there is no such thing as equivalent fork leg strength. One fork leg is always stronger than the other due to manufacturing i.e. layup/molding variation within the fork even though this could be less than 1%.

    Your TT, DT failure comment would be applicable if TT and DT had equivalent strength as with fork legs. They don't. Of course if one frame member fails either the TT or DT the other is likely to fail based upon rider load. A frame is truss and if a member is compromised, stresses goes way above what a remaining member can withstand. If not the case than any given frame would be overdesigned and weigh a lot more subtracting performance.
    Last edited by 11spd; 02-06-2018 at 05:15 AM.

  6. #56
    RoadBikeReview Member
    Reputation: velodog's Avatar
    Join Date
    Sep 2007
    Posts
    7,139
    Quote Originally Posted by mik_git View Post
    yeah, right at the leading edge where it's lying...

    also another ... something, maybe a cut...or nothing at all, at the top between the break in the fork and the bar, next to a white mark on the paver... could be nothing (both of them) or could be something telling
    I see that one also. The one I asked about looks like an impact tear, like factory feel mentioned, caused by running into a curb or sum such.

    And what 11spd said makes sense, about a failure happening in one leg, followed by the 2nd and not being symmetrical due to how the load is carried by the one fork blade.
    Too old to ride plastic

  7. #57
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by velodog View Post
    I see that one also. The one I asked about looks like an impact tear, like factory feel mentioned, caused by running into a curb or sum such.

    And what 11spd said makes sense, about a failure happening in one leg, followed by the 2nd and not being symmetrical due to how the load is carried by the one fork blade.
    The failures aren't truly symmetrical, and I wasn't suggesting that the two legs break simultaneously. I'm saying that neither fork leg is strong enough to support the load, and that both fork legs have the same weakest area. If one side fails at that weak area (due to a flaw on that side, for instance), the load goes to the other leg which is going to also fail at that same weakest point.


    So imagine a fork that has been designed to be most flexible at a point about 5" below the crown. The fork is designed to flex, and this mid span is where the layup was designed to allow more of it than at the crown or near the dropout. Then imagine that the right leg has a fold in the layup the creates a vertical void that runs from the crown to the dropout, weakening the entire length of the leg. Being equally flawed across the whole span, the failure point is going to default to that spot 5" down. One day that spot fails.

    The left leg is structurally sound, but wasn't designed to support that heavy an asymmetric load. So it bends toward the failure point, and like the right leg its weakest, most flexible spot is also 5" below the crown. So a moment after the right leg snaps the left follows at about the same area.

    Why wouldn't the left leg tend to break where the right was most likely to fail? Is there a reason the left would instead break somewhere along its span that is stronger?

    And if the right has a systemic flaw - like a lack of lamination that runs its full span, is it likely to break anywhere but its designed weakest point?
    Get a better saddle: www.kontactbike.com

  8. #58
    RoadBikeReview Member
    Reputation:
    Join Date
    Apr 2013
    Posts
    3,442
    Quote Originally Posted by cxwrench View Post
    So you're talking about a potential warranty issue/recall...on a 20 year old bike? Really?
    bikes don't have expiration dates. i think this is a legit concern. unless specialized is taking the position that bikes need annual safety inspections like airplanes its potentially troubling.

  9. #59
    RoadBikeReview Member
    Reputation: 11spd's Avatar
    Join Date
    Sep 2015
    Posts
    1,796
    Quote Originally Posted by Kontact View Post
    The failures aren't truly symmetrical, and I wasn't suggesting that the two legs break simultaneously. I'm saying that neither fork leg is strong enough to support the load, and that both fork legs have the same weakest area. If one side fails at that weak area (due to a flaw on that side, for instance), the load goes to the other leg which is going to also fail at that same weakest point.


    So imagine a fork that has been designed to be most flexible at a point about 5" below the crown. The fork is designed to flex, and this mid span is where the layup was designed to allow more of it than at the crown or near the dropout. Then imagine that the right leg has a fold in the layup the creates a vertical void that runs from the crown to the dropout, weakening the entire length of the leg. Being equally flawed across the whole span, the failure point is going to default to that spot 5" down. One day that spot fails.

    The left leg is structurally sound, but wasn't designed to support that heavy an asymmetric load. So it bends toward the failure point, and like the right leg its weakest, most flexible spot is also 5" below the crown. So a moment after the right leg snaps the left follows at about the same area.

    Why wouldn't the left leg tend to break where the right was most likely to fail? Is there a reason the left would instead break somewhere along its span that is stronger?

    And if the right has a systemic flaw - like a lack of lamination that runs its full span, is it likely to break anywhere but its designed weakest point?
    A fair hypothesis but slightly flawed. Where you perceive to be the flex point and most likely failure point of a fork...first or second break may not be where the fork will break. A mfg defect can be an area where the weakest point exists and unrelated to typical bend point of a fork. Failure point could even be 2 inches above the axle for example if the fork has voids in this area. Doesn't have to be higher up the fork as shown even though this area maybe the most common failure zone because the fork is designed to flex/displace 'generally' in this zone. Weakest link and poor molding practice is the biggest unknown.
    Last edited by 11spd; 02-06-2018 at 11:21 AM.

  10. #60
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
    Join Date
    Nov 2004
    Posts
    13,386
    Quote Originally Posted by Trek_5200 View Post
    bikes don't have expiration dates. i think this is a legit concern. unless specialized is taking the position that bikes need annual safety inspections like airplanes its potentially troubling.
    No kidding. But...as I've posted numerous times
    1) If a bike has a defect in materials and/or workmanship it's gonna shop a lot sooner than 10 years.
    2) It's exceptionally rare to have a fork fail like this as a result of defects in materials/workmanship. Not unheard of, but very rare.

    Your car theoretically needs to be inspected by the dealer/mechanic at set intervals, why wouldn't your bicycle? We already know that bike owners aren't going to waste time inspecting their own bikes.
    I work for some bike racers
    I've got some bikes, some guns,
    and a bunch of skateboards

  11. #61
    RoadBikeReview Member
    Reputation:
    Join Date
    Oct 2013
    Posts
    932
    When talking failure analysis, you really need to include the loads, and then the locations of greatest stress based on typical and then non-typical loads.

    Under normal riding, the typical load is vertical to support the bike. A non-typical load would be running into an object like a brick wall, where the major load is in the horizontal plane, and greatest stress would be the cantilever point at the top of the fork crown. Failure would occur in that case at the weakest point closest to the highest stress point. Right about where this failure occurred.

    And usually total failure comes from either one huge high stress event, or fatigue, where you get a small crack that then grows slowly with repeated reversing stress cycles. When the slow growing crack gets to a critical crack size, you get sudden failure. Hard to say which happened here, but usually you would see an external crack on close inspection.
    Fully agree forks don't suddenly break under normal riding.

  12. #62
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by 11spd View Post
    A fair hypothesis but slightly flawed. Where you perceive to be the flex point and most likely failure point of a fork...first or second break may not be where the fork will break. A mfg defect can be an area where the weakest point exists and unrelated to typical bend point of a fork. Failure point could even be 2 inches above the axle for example if the fork has voids in this area. Doesn't have to be higher up the fork as shown even though this area maybe the most common failure zone because the fork is designed to flex/displace 'generally' in this zone. Weakest link and poor molding practice is the biggest unknown.
    Nor did I say it couldn't be. I was just pointing out that certain types of molding flaws are going to make the weak point failure more likely, and the subsequent failure of the good leg will be in the same spot.

    This is an argument against the improbability of a symmetrical failures, NOT an argument that all failures must be symmetrical. So I don't understand your criticism - don't you agree that symmetrical failures do happen without garage door impacts?
    Get a better saddle: www.kontactbike.com

  13. #63
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by Z'mer View Post
    And usually total failure comes from either one huge high stress event, or fatigue, where you get a small crack that then grows slowly with repeated reversing stress cycles. When the slow growing crack gets to a critical crack size, you get sudden failure. Hard to say which happened here, but usually you would see an external crack on close inspection.
    Fully agree forks don't suddenly break under normal riding.
    You seem to be saying that forks do and do not suddenly fail. Which one is it?
    Get a better saddle: www.kontactbike.com

  14. #64
    RoadBikeReview Member
    Reputation: velodog's Avatar
    Join Date
    Sep 2007
    Posts
    7,139
    Quote Originally Posted by Kontact View Post
    You seem to be saying that forks do and do not suddenly fail. Which one is it?
    Actually I think he said that when a slow growing crack reaches a critical size , as in fatigue, it will let go suddenly, but under normal riding a healthy fork doesn't just suddenly break.
    Too old to ride plastic

  15. #65
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by velodog View Post
    Actually I think he said that when a slow growing crack reaches a critical size , as in fatigue, it will let go suddenly, but under normal riding a healthy fork doesn't just suddenly break.
    Under normal riding a healthy fork doesn't break suddenly or slowly. They don't break at all.

    For the fork to break there has to be something wrong with it. If there is something wrong with it that might be a huge void that doesn't show on the surface or a crack that does show on the surface. No one can say that only forks that have had surface cracks for X amount of time break.

    All broken forks have cracked surfaces.
    Get a better saddle: www.kontactbike.com

  16. #66
    RoadBikeReview Member
    Reputation: velodog's Avatar
    Join Date
    Sep 2007
    Posts
    7,139
    Quote Originally Posted by Kontact View Post
    Under normal riding a healthy fork doesn't break suddenly or slowly. They don't break at all.

    For the fork to break there has to be something wrong with it. If there is something wrong with it that might be a huge void that doesn't show on the surface or a crack that does show on the surface. No one can say that only forks that have had surface cracks for X amount of time break.

    All broken forks have cracked surfaces.
    Or, for a fork to break it has to run into something.
    Too old to ride plastic

  17. #67
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by velodog View Post
    Or, for a fork to break it has to run into something.
    If you run into something, doesn't that create the flaw that we've been talking about?

    Or do you mean the wheel hits something and the fork bends too far? Then it will fail despite not having a flaw, but that isn't "normal riding".



    Saying that forks do or do not "fail suddenly" is an observer issue, not a nugget of truth. If a fork is made with a critical flaw, we could say it has been failing since it was made. If you don't know about the flaw and it suddenly causes a catastrophic failure, that's going to appear to be sudden, regardless of how long a hidden failing existed.
    Get a better saddle: www.kontactbike.com

  18. #68
    RoadBikeReview Member
    Reputation: 11spd's Avatar
    Join Date
    Sep 2015
    Posts
    1,796
    Quote Originally Posted by cxwrench View Post
    No kidding. But...as I've posted numerous times
    1) If a bike has a defect in materials and/or workmanship it's gonna shop a lot sooner than 10 years.
    2) It's exceptionally rare to have a fork fail like this as a result of defects in materials/workmanship. Not unheard of, but very rare.

    Your car theoretically needs to be inspected by the dealer/mechanic at set intervals, why wouldn't your bicycle? We already know that bike owners aren't going to waste time inspecting their own bikes.
    And a further nuance. Inspection in many instances won't reveal an accident in waiting. An X-ray is more fool proof...what Specialized does for their recalls. They don't discard all returned forks...only a subset that reveal weakness. This isn't detectable by the naked eye.

  19. #69
    RoadBikeReview Member
    Reputation: velodog's Avatar
    Join Date
    Sep 2007
    Posts
    7,139
    Quote Originally Posted by Kontact View Post
    If you run into something, doesn't that create the flaw that we've been talking about?

    Or do you mean the wheel hits something and the fork bends too far? Then it will fail despite not having a flaw, but that isn't "normal riding".
    That's right, and that's why I find it hard to believe that this didn't happen "JRA".

    At 9/9:30 on the front tire in the picture of the complete bike, broken fork and front wheel I see what looks like a tear in the tire that could easily have happened in an impact with a curb or pot hole or sumsuch.

    The OP was found in a heap and taken to the hospital with facial damage. The shock of an accident will often times erase all memory of the incident which could explain the cyclist not remembering hitting anything.

    I once went from riding in a drizzle to having my clothes cut off in an emergency ward, and still don't recall being ass ended by an automobile that was traveling at an estimated 70mph, yet my partner says that I never lost conscientiousness.
    Too old to ride plastic

  20. #70
    RoadBikeReview Member
    Reputation: 11spd's Avatar
    Join Date
    Sep 2015
    Posts
    1,796
    Quote Originally Posted by Kontact View Post
    Nor did I say it couldn't be. I was just pointing out that certain types of molding flaws are going to make the weak point failure more likely, and the subsequent failure of the good leg will be in the same spot.

    This is an argument against the improbability of a symmetrical failures, NOT an argument that all failures must be symmetrical. So I don't understand your criticism - don't you agree that symmetrical failures do happen without garage door impacts?
    No idea what you are talking about either...not a bit of it including your oblique reference to 'without garage door impacts'. Bizarre.

  21. #71
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by 11spd View Post
    No idea what you are talking about either...not a bit of it including your oblique reference to 'without garage door impacts'. Bizarre.
    I'm sorry you are unable to follow the thread.
    Get a better saddle: www.kontactbike.com

  22. #72
    Happily absent RBR Member
    Reputation: Kontact's Avatar
    Join Date
    Apr 2011
    Posts
    3,940
    Quote Originally Posted by velodog View Post
    That's right, and that's why I find it hard to believe that this didn't happen "JRA".

    At 9/9:30 on the front tire in the picture of the complete bike, broken fork and front wheel I see what looks like a tear in the tire that could easily have happened in an impact with a curb or pot hole or sumsuch.

    The OP was found in a heap and taken to the hospital with facial damage. The shock of an accident will often times erase all memory of the incident which could explain the cyclist not remembering hitting anything.

    I once went from riding in a drizzle to having my clothes cut off in an emergency ward, and still don't recall being ass ended by an automobile that was traveling at an estimated 70mph, yet my partner says that I never lost conscientiousness.
    We don't know what happened, and I don't know why that demonstrates that it failed because of a pothole or not.

    Regardless, if the OP hit something with his wheel, his fork still failed symmetrically without first being impacted while on a roof rack. My point has simply been that symmetrical failures are quite possible without a surface impact because both legs have the same weak points.


    This isn't a recall issue, because as CX pointed out, there aren't a bunch of these forks failing. But that doesn't mean this particular example didn't fail from a production flaw, or that it didn't fail from hitting a pothole.


    But that really has me wondering what sort of wheel impact could break a carbon fork. My experience is that the fork does a good job of stopping the bike and sending the rider flying over the handlebars, rather than the fork breaking because the rider is so implacably glued to the bike that his mass is enough to shear both legs. Is that even possible?
    Get a better saddle: www.kontactbike.com

  23. #73
    RoadBikeReview Member
    Reputation:
    Join Date
    Oct 2013
    Posts
    932
    found this article which has lots of good info
    https://cyclingtips.com/2015/08/what...-carbon-frame/

    The point I made about fatigue above applies mainly to metals like steel or alu. Carbon fiber is slightly different, but apparently still susceptible to failure after repeated stress reversal cycles, especially after damage where the resin matrix breaks down and then internal fibers are broken. Article says same thing can happen if defective from new.

  24. #74
    RoadBikeReview Member
    Reputation: 11spd's Avatar
    Join Date
    Sep 2015
    Posts
    1,796
    Quote Originally Posted by Kontact View Post
    I'm sorry you are unable to follow the thread.
    I follow the thread perfectly. You may notice...not....that pretty everybody struggles with your obtuse ramblings.

  25. #75
    RoadBikeReview Member
    Reputation: 11spd's Avatar
    Join Date
    Sep 2015
    Posts
    1,796
    Quote Originally Posted by Z'mer View Post
    found this article which has lots of good info
    https://cyclingtips.com/2015/08/what...-carbon-frame/

    The point I made about fatigue above applies mainly to metals like steel or alu. Carbon fiber is slightly different, but apparently still susceptible to failure after repeated stress reversal cycles, especially after damage where the resin matrix breaks down and then internal fibers are broken. Article says same thing can happen if defective from new.
    Exactly.

Page 3 of 9 FirstFirst 12345 ... LastLast

Similar Threads

  1. Replies: 9
    Last Post: 08-19-2012, 12:12 PM
  2. Replies: 3
    Last Post: 01-26-2008, 08:45 PM
  3. Any frame/fork difference between 2005 Specialized Roubaix Elite and Comp?
    By Mr Bentwrench in forum Bikes, Frames and Forks
    Replies: 0
    Last Post: 01-25-2008, 12:21 PM
  4. Scattante frame/fork defect?
    By bcyclist in forum Bikes, Frames and Forks
    Replies: 18
    Last Post: 06-17-2007, 01:17 PM
  5. Advice needed for new frame defect (long-ish)
    By KeithNYC in forum Bikes, Frames and Forks
    Replies: 5
    Last Post: 11-05-2005, 01:36 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT ROADBIKEREVIEW

VISIT US AT

roadbikereview.com and the ConsumerReview Network are business units of Invenda Corporation

(C) Copyright 1996-2018. All Rights Reserved.