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  1. #26
    Sup
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    I knew the new xt brakes were strong but WOW

    Sj
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  2. #27
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    Ask the manufacturer...

    Quote Originally Posted by bugshield View Post
    Any info on identifying heat treated and untreated forks? I am, so far, unsuccessful in my search.

    I sure would like to identify the problem and be able to identify that the replacement does not have the problem.

    Thanks.
    ...would be the best way. If you had access to a hardness testing machine you could sample the fork top to bottom and figure it out that way. Like with any of the gadgets on this page: Hardness Testers Portable Digital Bench Rockwell

    As far as what a manufacturer considers "heat treating" is wide open to interpretation; "heat treatment" can be used to make a part softer/harder (weaker/stronger) depending on the goal for the individual part. (A part that's too hard will fail by snapping whereas bending is a better way to have most things fail---stronger is not necessarily always better)

    Aluminum forks very likely have undergone post-fabrication heat treating, steel forks are a maybe. From what I can find with a quick google search is that some BMX forks receive heat treatment after welding; other MTB forks may be built with parts that have had heat treating prior to assembly---which the Mfgs interpret as the fork being "heat treated".

    The problem with this marketing ploy is that the heat treatment the fork blades have received (to relieve stress from the hydro-forming operation) is nullified when the blades are assembled---definitely in areas that are being welded; maybe in areas that have been brazed. The area that your fork folded is right between two such areas; the brake mount being welded and the bottle mount being brazed. The perfect storm for a stress riser---even with proper heat treatment that's where failure would be expected.

    How bicycle forks are tested is pretty interesting and revealing; here's a paper (fairly recent; 2010) from a couple of engineering students at WPI:

    http://www.google.com/url?sa=t&rct=j...49y9h2Mx5jsPfw

    Well worth glancing through the 101 pages; especially the ASTM fork testing protocol posted in the appendix. Keep in mind that this test is mostly concerned with the fatigue life of bike forks; not so much the ultimate strength. What is most interesting is that this test was formulated before disk brakes were much in use; the loads created by their use are not considered at all. Perhaps these loads "fell through the cracks" at Surly also?
    The views and opinions expressed here are those of the author and do not represent any policy of the CA Dept. of Parks & Rec.

  3. #28
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    Quote Originally Posted by pliebenberg View Post
    ...would be the best way. If you had access to a hardness testing machine you could sample the fork top to bottom and figure it out that way. Like with any of the gadgets on this page: Hardness Testers Portable Digital Bench Rockwell

    As far as what a manufacturer considers "heat treating" is wide open to interpretation; "heat treatment" can be used to make a part softer/harder (weaker/stronger) depending on the goal for the individual part. (A part that's too hard will fail by snapping whereas bending is a better way to have most things fail---stronger is not necessarily always better)

    Aluminum forks very likely have undergone post-fabrication heat treating, steel forks are a maybe. From what I can find with a quick google search is that some BMX forks receive heat treatment after welding; other MTB forks may be built with parts that have had heat treating prior to assembly---which the Mfgs interpret as the fork being "heat treated".

    The problem with this marketing ploy is that the heat treatment the fork blades have received (to relieve stress from the hydro-forming operation) is nullified when the blades are assembled---definitely in areas that are being welded; maybe in areas that have been brazed. The area that your fork folded is right between two such areas; the brake mount being welded and the bottle mount being brazed. The perfect storm for a stress riser---even with proper heat treatment that's where failure would be expected.

    How bicycle forks are tested is pretty interesting and revealing; here's a paper (fairly recent; 2010) from a couple of engineering students at WPI:

    http://www.google.com/url?sa=t&rct=j...49y9h2Mx5jsPfw

    Well worth glancing through the 101 pages; especially the ASTM fork testing protocol posted in the appendix. Keep in mind that this test is mostly concerned with the fatigue life of bike forks; not so much the ultimate strength. What is most interesting is that this test was formulated before disk brakes were much in use; the loads created by their use are not considered at all. Perhaps these loads "fell through the cracks" at Surly also?
    Very interesting. Thank you for posting.

    Having Googled a bit for things like "surly" and "heat treated fork" it is not immediately clear to me that Surly claims this or any fork is heat treated. Most of the results reference the chainstays of the 1x1. I wonder if the heat treating angle has only been dropped by the advertising folk or if the fact that it is not mentioned means that it was not done.

    Looking at the 2012 catalog available as a PDF, Surly makes several claims about heat treating for other parts so I'd guess the absence of a heat treating claim is at least possibly meaningful.

    PS. I am not an engineer though I occasionally like to talk like one and try to apply reason to the questions I encounter.

  4. #29
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    Quote Originally Posted by bugshield View Post
    I think that goes without saying.

    The question is, Do I trust the replacement?
    I would assume the replacement will be "normal" and should be fine. You would be smart to test it out by gradually increasing the stress you put on it.

    I own a number of Surly bikes and they have all be bomber.
    Safe riding,

    Vik
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  5. #30
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    Quote Originally Posted by vikb View Post
    I would assume the replacement will be "normal" and should be fine. You would be smart to test it out by gradually increasing the stress you put on it.

    I own a number of Surly bikes and they have all be bomber.
    Ha ha. Thanks. My LBS said something similar when I was debating Surly/Salsa/9:Zero:7.

    I am enjoying your blog BTW.

  6. #31
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    I'm 240lbs, using Hayes Nine Carbons with 8" rotors on my Enabler fork with no problems like this, thankfully. However, there is a moderate amount of front flex (noticed on pavement). My real issueis that the brakes howl with light to moderate pressure and cause a reasonance throughtout the front end. More annoying than anything, and I'd like to find a solution.
    Wowsa...

    Side note to trailmaker: My Enabler fork did the exact same thing when I switched from BB7 to SLX...Howling and resonance with moderate pressure. Close inspection showed the mounting bosses were a tiny bit skewed--brake wouldn't 'square up' with the rotor, so pads were contacting at an angle. I dressed the bosses on the fork with a file until they appeared visually parallel with the rotor, just a few strokes really. Reattached adapter and now howl is gone. In retrospect the bb7's were unusually noisy as well. Willing to bet that's what's up with yours...

  7. #32
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    Quote Originally Posted by montana_ben View Post
    Wowsa...

    Side note to trailmaker: My Enabler fork did the exact same thing when I switched from BB7 to SLX...Howling and resonance with moderate pressure. Close inspection showed the mounting bosses were a tiny bit skewed--brake wouldn't 'square up' with the rotor, so pads were contacting at an angle. I dressed the bosses on the fork with a file until they appeared visually parallel with the rotor, just a few strokes really. Reattached adapter and now howl is gone. In retrospect the bb7's were unusually noisy as well. Willing to bet that's what's up with yours...
    is it possible a brake post face tool would cure this?? say from a LBS?

  8. #33
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    is it possible a brake post face tool would cure this?? say from a LBS?
    Definitely--I guess I should have said, your i.s. mount tab needs to be faced, take it to your LBS. Just lazy and grabbed a file... Correct tool: Park Tool Co. ParkTool Blog Disc Brake Mount Facing (IS type) with DT-1

    Sorry to wander off-thread, bent fork is much more exciting.

  9. #34
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    Quote Originally Posted by montana_ben View Post
    Definitely--I guess I should have said, your i.s. mount tab needs to be faced, take it to your LBS. Just lazy and grabbed a file... Correct tool: Park Tool Co. ParkTool Blog Disc Brake Mount Facing (IS type) with DT-1

    Sorry to wander off-thread, bent fork is much more exciting.
    we on the same page so no worries and yes 'bent fork' deserves attention.

  10. #35
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    PSA; don't do "stoppies" on rigid disc brake forks...

    Quote Originally Posted by bugshield View Post
    Very interesting. Thank you for posting.

    Having Googled a bit for things like "surly" and "heat treated fork" it is not immediately clear to me that Surly claims this or any fork is heat treated. Most of the results reference the chainstays of the 1x1. I wonder if the heat treating angle has only been dropped by the advertising folk or if the fact that it is not mentioned means that it was not done.

    Looking at the 2012 catalog available as a PDF, Surly makes several claims about heat treating for other parts so I'd guess the absence of a heat treating claim is at least possibly meaningful.

    PS. I am not an engineer though I occasionally like to talk like one and try to apply reason to the questions I encounter.
    I'm not a mechanical engineer either but I've rubbed elbows with many over the years(before retirement I was involved with the fabrication of all sorts of metal thingys requiring an engineering stamp)---I'm a sucker for eloquent engineering and study it as a hobby.

    So I did some quick calculations on the Pugsly fork and my results are a little scary---if my assumptions are correct you'd expect the fork to fail under hard braking. (ASS_U_ME; makes an "ass" out of "you" and "me"!)

    I won't go too far into the detail of my assumptions other than to say I used 25 mm diameter 1.0 mm wall 4130 normalized tube at the failure point. Plus the rider is a sack of bricks weighing 230 lbs. Plus instant brake application = failure every time. (215 lbs for the rider plus 15 lbs for some of the bike's mass)

    That the rider is a blob of protoplasm and that brakes don't grab instantly is why folks can get away with "stoppies" and such. Rim brakes are much easier on the fork; it appears to me that with disc brakes at the instant of brake application nearly all the stress goes through the left fork blade.

    Maybe all this will draw out a "real" engineer (lurking???); it'd be great to see a FEA done on a disc brake fork leg.
    The views and opinions expressed here are those of the author and do not represent any policy of the CA Dept. of Parks & Rec.

  11. #36
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    Quote Originally Posted by pliebenberg View Post
    I'm not a mechanical engineer either but I've rubbed elbows with many over the years(before retirement I was involved with the fabrication of all sorts of metal thingys requiring an engineering stamp)---I'm a sucker for eloquent engineering and study it as a hobby.

    So I did some quick calculations on the Pugsly fork and my results are a little scary---if my assumptions are correct you'd expect the fork to fail under hard braking. (ASS_U_ME; makes an "ass" out of "you" and "me"!)

    I won't go too far into the detail of my assumptions other than to say I used 25 mm diameter 1.0 mm wall 4130 normalized tube at the failure point. Plus the rider is a sack of bricks weighing 230 lbs. Plus instant brake application = failure every time. (215 lbs for the rider plus 15 lbs for some of the bike's mass)

    That the rider is a blob of protoplasm and that brakes don't grab instantly is why folks can get away with "stoppies" and such. Rim brakes are much easier on the fork; it appears to me that with disc brakes at the instant of brake application nearly all the stress goes through the left fork blade.

    Maybe all this will draw out a "real" engineer (lurking???); it'd be great to see a FEA done on a disc brake fork leg.
    VERY interesting!

    I was wondering along those lines. I figure the ability to load a fork would have roughly to do with: the weight of the bike/rider combination, the ability of the tire to keep traction, the ability of the rider to keep the back end down, the rotational mass of the tire/wheel, and the ability of the brakes to stop all that.

    Obviously these big Husker Dus have some awesome traction and so do these M785 brakes. I'm a big guy and know to throw my weight back on a hard stop...

    This happened on packed sand, by the way. Here is a picture of the tire track. You can see where the front tire was scrubbing for about 16" inches then broke left (right in the picture) when the left fork leg buckled. http://sheepcamp.com/~ben/pics/BentFork/IMG_0615.jpg

  12. #37
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    Quote Originally Posted by pliebenberg View Post
    I won't go too far into the detail of my assumptions other than to say I used 25 mm diameter 1.0 mm wall 4130 normalized tube at the failure point. Plus the rider is a sack of bricks weighing 230 lbs. Plus instant brake application = failure every time. (215 lbs for the rider plus 15 lbs for some of the bike's mass)
    Presumably there is no such thing as instant 100% brake application. Looking at my tire tracks you can see that I was at least 16-inches into my stop before the fork buckled and a substantial part of the energy would have already been dumped in that distance.

  13. #38
    R.I.P. Pugsley.
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    I must say that the last few hours i have been looking at the fork on my Karate Monkey quite a few times.
    And i must say it looks a bit flimsy.
    I'm starting to wonder how it will hold up to my 265 pounds once it's finished....

  14. #39
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    I don't think heat treatment would have been the problem. Cr-Mo steel is sometimes heat treated after welding to make it less brittle, but this is only necessary with thick material, not thin bicycle tubing. It looks like those forks are just not strong enough for disk brakes. Maybe the material was mild steel instead of chrome molybdenum alloy steel.

  15. #40
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    I wouldn't spend too much time analyzing what happened to one fork. Surly forks seem to be pretty robust and you don't hear of failures like this often - in fact I've never seen anything like this with a Surly fork. So it's quite possible there was something unusual going on with this particular fork.

    A more common complaint with Surly forks are that they are too stiff and overbuilt.
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  16. #41
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    It's a defective fork plain and simple. The OP should have taken this up with Surly long before posting it here.

  17. #42
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    Quote Originally Posted by Bearbait View Post
    It's a defective fork plain and simple. The OP should have taken this up with Surly long before posting it here.
    We should be told of this type of failure. If just one person checks their fork and is saved from a faceplant it's worthwhile.

    Meanwhile pliebenberg's post above raises a few questions...
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  18. #43
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    Quote Originally Posted by Bearbait View Post
    It's a defective fork plain and simple. The OP should have taken this up with Surly long before posting it here.
    2nd'd!!!

  19. #44
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    Quote Originally Posted by Bearbait View Post
    It's a defective fork plain and simple. The OP should have taken this up with Surly long before posting it here.
    perhaps thats already been done in some form or fashion. There's absolutely nothing wrong with bringing it here if done in a respectful way which is exactly what bugshield has done, no trash talk, no name calling just sharing an issue, a very important issue for us ALL.

  20. #45
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    ^^^ Yep, it was done with best intentions. He wasnt coming on with guns blazing pointing blame. Its good to share so others can inspect their forks - who's heading to the local playing fields to brake/break test their Surly forks ???

    Here's the way not to act

    Should be cut and dry warranty, it was better for you to find the weakness rather than the better half.
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  21. #46
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    It's All Good. Fellers;

    Yes, sorry for the little thread segue back there, but I have been slightly worried that continued resonance through the fork blades might cause a failure like in the OP. My weight plus the big rotor plus the fact that I ride this thing like a regular trail bike (hard!) gives me some pause. Nothing, yet........

    If this thread causes everyone to go out and look at their fork, and now do so on a regular basis, then that is a good thing for us all. It's even good for the manufacturer.
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  22. #47
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    Good point, I guess I should have clarified that better. If there is a widespread issue I'm sure fork owners will hear about it in a more formal manner as it is obviously a serious safety concern! You're right, awareness is good... I've been riding surly forks for almost 10 years and know they design their parts well and overkill. Major ouchie with that carbon fork. wow.

  23. #48
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    Might it be possible that not having the rotors and shoes bedded in produced more friction than they otherwise would during their normal service life? I tend to agree that this particular fork was defective, but with due respect to the OP, I'd suggest that the bedding-in period may not be the best time to do stoppies.

    In any case, I hope it's not the design, because I've just installed two of these; one on my 907 and the other on my daughter's Necro. Neither of us is real hard on the equipment, but I was doing a bit of enthusiastic singletrack riding on mine yesterday.

  24. #49
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    Smartphone accelerometers

    So I spent some time the last couple of days doing (or trying to do) "stoppies" on my Pugsly and recording them on my iPhone using various "g force" apps. None of the apps I tried worked perfectly but showed that with the right software the iPhone could be a great little accelerometer/datalogger. When I did my previous calculations on the stresses the fork sees under hard braking I came up with the numbers that about the most I'd trust the Pug's fork to would be around 1/2 g deceleration; and also 1/2 g should yield a stoppie.

    The first trials yesterday were a bit of a non-event; it had rained the night before and no matter how hard I tried it the front tire (Nates F/R) would slide before the rear end lifted---both on pavement and on my gravel driveway. (I was able to easily get some stoppies on a couple of my 29ers though) As things dried out the Nate got enough grip and I was able get into the stoppie zone. Here are some of the marks left on the gravel:

    The length of the "skid" (from the partially locked front wheel) correlates well with the braking effort to get a stoppie from the 10 mph target speed I was using.

    Here's a screen grab from "CMS Lap Timer"; a $0.99 app:

    The graph shows 2 "near stoppies"; I didn't hold the entry speed steady for very long so part of the deceleration is occurring from the positive part of the curve---the -.15 g is probably at least twice that. Also the 5.9 MPH speed is from the GPS and is an average over ??? distance (this app is optimized for car racing)

    Here's using "gForce"; a free iPhone app:

    This shows 5 events; the 2.3 g is an actual stoppie but is showing the shock of the rear end slamming down---not the braking effort. The other numbers (0.4 ~ 0.8 g) are more of what I would expect but probably a bit on the high side.

    FWIW my brakes are Avid Juicy Sevens' and a 180mm rotor on the front; not a particularly powerful brake IMHO. I don't remember what the pads are but they're probably organics. The iPhone was "jury-rigged" mounted to the rear rack (why that 2.3 g slam-down reading)
    The views and opinions expressed here are those of the author and do not represent any policy of the CA Dept. of Parks & Rec.

  25. #50
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    Quote Originally Posted by pliebenberg View Post
    So I spent some time the last couple of days doing (or trying to do) "stoppies" on my Pugsly and recording them on my iPhone using various "g force" apps.
    VERY cool.

    I take it that your fork survived all this in style. What fork do you have?

    I wouldn't know where to start the calculations on how much load this fork got when it bounced off the second half of a double but I would guess SUBSTANTIALLY more than the one I folded. Pugsley dirt jump disaster!

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