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  1. #1
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    Q: Slack all-mountain hardtail failures?

    Ok, this has been kinda 'covered' in an assortment of other threads, but I want the final word
    What is your experience with frame failures on 29er frames resulting from long-travel forks?

    I'm designing a bike for a friend and he wants an all-mountain rig, something similar to the Kona Honzo.
    So a 68 HTA, X-fusion Trace 29er fork (110/140mm), and between 16" - 16.5" chainstays. I wasn't planning on using a gusset like on the Honzo. I was just planning to overbuild the frame with stuff like a 38mm Supertherm (1/7/1) downtube, PMW head tube, seat tube sleeve, 9/6/9 TT, etc.

    I know some builders won't make a 29er for any suspension fork over 100mm because the axle to crown is too long...and there would be too much of a lever to wrench on the downtube and cause downtube failure.

    My question is...in your experience, is that based on experience/reality/testing or is it precautionary because it just seems sketchy?

    The guy I'm building it for is an 'active' rider, not heavy, but rails and jumps everything in sight. He is the perfect product tester....heh.

    thoughts and recommendations...?

  2. #2
    pvd
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    There's no issue. As long as the down tube is strong enought and the head tube long enough the bike will be strong enough.

    The real question is, why? Long travel 29ers are garbage. If you are looking for something with a 150mm fork, 26 or 650 are far better options. A long 29er gets so long and combersome that the front wheel snags trees. Also, it is extremely difficult to get the handlebars anywhere near the right riding position even with a crazy short head tube.

  3. #3
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    Quote Originally Posted by pvd View Post
    The real question is, why? Long travel 29ers are garbage. If you are looking for something with a 150mm fork, 26 or 650 are far better options. A long 29er gets so long and combersome that the front wheel snags trees. Also, it is extremely difficult to get the handlebars anywhere near the right riding position even with a crazy short head tube.
    Thanks PVD, appreciate the feedback.
    As far as why do it? It's just what he's asking for and I either need to tell him 'NO' and build him what I think he wants and hope he likes it, or just build what he is asking for and have him see for himself that it may suck.

    He's actually not thinking of a 150 fork but a 110 X-fusion Trace (which BTW, if anybody can tell me the offset that'd be awesome...not on their website). I'd build it to the 110 ATC so it wouldn't be that high in the front. But i see the issue - longer travel forks = longer ATC but need a longer HT to support that torque (along with a beefier DT) so the bars will be higher than wanted even with a zero stack headset on top, etc.

  4. #4
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    Hey;

    I'd say if you have to resort to shorter than a 5" HT, zero-stack, no spacers, a 6-10* stem flipped upside down, and a flat bar, it would indicate another platform is called for. On the other hand, if you are like me and my RIP9 with a 145mm HT, 40mm of spacers, 50mm riser bar on a Thompson 10* stem, and your bars are still over an inch below the seat, you won't have a problem with the front being too high. That is NEVER a problem for me. Quite the reverse. I've used a 7" HT on both of my Fatbikes, which just gets the bars/seat level, and am seriously considering using an 8 in the future. I doubt many people are using an Enabler fork uncut!

    I'd say if the guy isn't 6' or more, and likes to pop and squirt off everything in sight, you might do him a favor by suggesting 650B. Unless he is willing to gamble.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  5. #5
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    Thanks John!

    He's over 6'2" so I'll be using a 130 headtube or thereabouts. He has super long legs to boot so I don't think bar height will be an issue. I'm more worried about getting the bike to feel like he wants it. I don't think with a front center of 740mm that is possible to get that whippy feel, but he wants a top tube and stem of a certain length...

  6. #6
    pvd
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    A well designed and set-up mountain bike will allow the front end to do a full 180 degree spin in the event of a crash. This is especially important for racers. This is important as it prevents the top tube from being destroyed in a mild crash. A properly set up race bike will also have cables and hoses set up that allows for 180 degrees of spin as well. This is so that in the event of a crash the bike can be remounted instantly and riden as the cables havent been compromised. Without this, the rider will have to waste time without a functioning bike. Common mistake among noob mechanics.

    Essentially, head tubes (or HT/TT joints lower) typically have to be shorter than you think. Commonly though, mtb riders have their handlebars far too high. Best to do a decent fit to get numbers right.

  7. #7
    Nemophilist
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    Hey Whit;

    Jus talking out my backside here, cause I don't know much... except what I know.

    A 740FC sounds excessively long for someone that height, unless he DOES have freaky long arms/legs. When I built my Humvee Fatty, I looked closely at the XL Salsa Mukluk, and also factored in my wonderfully roomy XL RIP9 specs, which are surprisingly close to each other in some ways. I'm 6'5" with a 36.5 inseam and a 35.5 sleeve. The Humvee ended up with a 742mm FC. On the trails in summer, it feels fabulous. Lots of room to move around and easy to stay behind the bars for rough techy terrain. Interestingly, in the snow it feels REALLY long, and I was thinking about popping on a shorter stem than the 100mm it has on it to see if that would "shorten" it.

    I'd LOVE to be able to lower my bars down for some climbing help. Problem is, my old bones just wont stand it no mo! Meh... I'm just a trail plonker anyhow.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
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  8. #8
    RCP Fabrication
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    Front center is a meaningless comparison with head angles getting as slack as people are wanting them these days. All mountain bikes are not XC race bikes.

  9. #9
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    OT: How so?

    Are you arguing that the positioning of the front wheel doesn't matter or something? Or that longer is always better when you're building a bike with a slack head tube angle?

    If you just mean that comparing a DH bike to an XC bike based on front center isn't useful, I agree. But the starting point of any design should be weight balance and if you're completely ignoring front center, that's not good. Long and slack *might* be what you're after, but slack and short can be good too, depending on what you're going for. If you just set the TT length and HT angle and leave FC to end up wherever it ends up you are not doing your job as a designer, IMO.

    Back on topic: That DT will handle a 150mm 29er fork just fine. You don't need the Paragon head tube for strength, the TT stuff will work fine there too if you don't care about the rings/shape.

    -Walt

    Quote Originally Posted by RCP FAB View Post
    Front center is a meaningless comparison with head angles getting as slack as people are wanting them these days. All mountain bikes are not XC race bikes.
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  10. #10
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    Quote Originally Posted by Walt View Post
    If you just mean that comparing a DH bike to an XC bike based on front center isn't useful, I agree.
    That's what I was referring to.

  11. #11
    pvd
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    Trailbikes and enduro bikes will have much longer front centers compared to XC bikes. It's a lot more important to get your FC right than having some imaginary top tube length.

  12. #12
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    Quote Originally Posted by pvd View Post
    Trailbikes and enduro bikes will have much longer front centers compared to XC bikes. It's a lot more important to get your FC right than having some imaginary top tube length.
    This is what I'm after. How long is too long for these types of bikes?
    It's a problem with people that focus on the bikes they have ridden and the top tube lengths they know. They have a XC bike with 71 deg hta and a 24.67" top tube and then want an enduro bike that they're going to use as their new XC bike and they want a 68 deg hta and that same top tube length, and the front center goes through the roof! Especially with a 51mm offset fork. They try to account for the change in handling by using of a really short stem and that obviously doesn't do jack to the long FC.

  13. #13
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    Quote Originally Posted by Walt View Post

    That DT will handle a 150mm 29er fork just fine.

    -Walt
    Thinking about this. So nobody on this list has seen or themselves cracked a 29er frame at the downtube because of a long travel fork?

    If that's the case I'm going to sub a 35mm Supertherm or even a 9/6/9 DT and ditch the 38 Supertherm. That thing feels like a baseball bat (a heavy one).

  14. #14
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    FWIW (not much), I'd probably use the 9/6/9 38mm tube TT has HOX2D01.

    Another way to think of the problem: if a 29er fork over 100mm is "too long," then you couldn't have a 200mm 26" fork.

  15. #15
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    Well...

    I've seen plenty of DT's folded in crashes (ie shorted that double, hit an invisible ditch, ran into a tree/big rock/parked car/garage) but IMO in all of those cases the fork length was irrelevant. I'm sure you can use a tube that is too weak if you try hard, but I think you'd have trouble with frame stiffness and ride feel long before you'd fold the DT just riding off a drop or something.

    The Supertherm is nice for dent resistance, for sure. It does feel like a softball bat in your hands! For the extra 100g, sometimes that's nice to have.

    -Walt

    Quote Originally Posted by Meriwether View Post
    Thinking about this. So nobody on this list has seen or themselves cracked a 29er frame at the downtube because of a long travel fork?

    If that's the case I'm going to sub a 35mm Supertherm or even a 9/6/9 DT and ditch the 38 Supertherm. That thing feels like a baseball bat (a heavy one).
    Waltworks Custom Bicycles
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  16. #16
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    Thanks

    I will go with the 35mm Supertherm just to be safe. I've used the 38mm 9/6/9 before and it saves some weight and it'd probably be fine with that too but better to be safe on this dude's bike IMO since he'll test it.

    The point of the 200mm fork on a 26er is a good one. For front suspension seems like you can get away with more. I understand why some may not want to put a long *rigid* fork on a frame (built for a 120+ suspension fork)...but if the frame is built for either (like we're talking about) what's the limit for this type of conversion? Seems like it's settled in at (or nobody will dare go over) 468 ATC. A longer rigid fork can offer more 'suspension' but could end up compromising the frame's integrity - too long a lever arm. I see this happening with people turning a bike into a singlespeed and just slapping on a rigid fork, and the geometry totally changes to be steeper & lower and it rides crappier.

    Mostly just pontificating here but just wondering what y'all think. The new Surly Krampus has an ATC of 483 likely to account for the big Knard tires. So maybe they're safe in doing that because they're using beefier (straight gauge?) tubing but that goes against the 468 "limit." They must have done some testing to see how the frames fared before releasing this bike...?

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