Curved seat tubes wanted- Mtbr.com
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  1. #1
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    Curved seat tubes wanted

    I really like the look of the curved seat tube on hardtails and gravel frames. Iím starting to see this more and more and especially on metal frames Iím sure it helps create a more supple feel.
    I bought an Esker Hayduke but the small size has very little curve. Now Iím looking for a gravel frame and intend to build up as a fat tire rig with 650b wheels.
    Any suggestions?
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  2. #2
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    A Curved Tube is no more supple than a straight one. A seat tube is situated as part of a triangle towards the head tube and propped up by 2 triangles to the rear. No place for movement here. It's done for either space reasons (rear wheel clearance) or is pleasing to the eye.

    Eric
    If I don't make an attempt, how will I know if it will work?

  3. #3
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    I looks nice and extra tire/wheel clearance is always nicer than be limited to narrow tires.
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  4. #4
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    Quote Originally Posted by Eric Malcolm View Post
    A Curved Tube is no more supple than a straight one. A seat tube is situated as part of a triangle towards the head tube and propped up by 2 triangles to the rear. No place for movement here. It's done for either space reasons (rear wheel clearance) or is pleasing to the eye.

    Eric
    Iím not sure how noticeable it will be?, but a triangle with a curved or bent side is definitely more prone to flex than a straight side. A curved tube will deform far more easily in both compression and tension than a straight one. This ability for the curved tube to change in length will just allow the other 2 straight sides to bend slightly, or the opposite angle to act as a hinge.

  5. #5
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    Quote Originally Posted by Cord View Post
    Iím not sure how noticeable it will be?, but a triangle with a curved or bent side is definitely more prone to flex than a straight side. A curved tube will deform far more easily in both compression and tension than a straight one. This ability for the curved tube to change in length will just allow the other 2 straight sides to bend slightly, or the opposite angle to act as a hinge.
    I think the force needed to deform a curved seat stay is far greater than any cyclist could possibly generate, especially as any deformation in regards to a change in ride characteristics, in this case suppleness. This from a rider with curved seat stays.

  6. #6
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    Quote Originally Posted by calstar View Post
    I think the force needed to deform a curved seat stay is far greater than any cyclist could possibly generate, especially as any deformation in regards to a change in ride characteristics, in this case suppleness. This from a rider with curved seat stays.
    I was thinking seat tubes more than swat stays, but itís all the same mechanism. The shock loading from an 70 or 80 kg rider landing a jump on a hardtail, or smashing through a pot hole on a gravel bike must impart a huge amount of energy. This force could be multiplied if seated on a long seatpost. Just thinking out loud more than stating any scientific data.

  7. #7
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    Quote Originally Posted by Cord View Post
    I was thinking seat tubes more than swat stays, but itís all the same mechanism. The shock loading from an 70 or 80 kg rider landing a jump on a hardtail, or smashing through a pot hole on a gravel bike must impart a huge amount of energy. This force could be multiplied if seated on a long seatpost. Just thinking out loud more than stating any scientific data.
    Sorry, I read "seat stay" into your post rather than seat tube, but I think it's the same story with deformation. I'm also thinking pretty much all the the force would be absorbed by the tires until they're compressed to the point of rim contact to ground. Yeah, I'm "thinking out loud" as well, no reference to empirical data.

  8. #8
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    Iím glad you read seat stay, who knows what a swat stay is!!

    Talking mountain bikes, thereís a fair amount of damping built into a tyre. In the time it takes to deform the casing and plies to the rim, a large portion of that energy will have already been transferred on up the chain via spokes and hub etc.

    Iíve ridden carbon hardtails that are noticeably harsher to ride than steel. Iíd love to know measurements of how much deflection is actually occurring. Both from an engineering stand point to see what a frame goes through, but also to understand what you can actually ďfeelĒ in real world terms.

    Iím talking/thinking vertical deflection here, lateral deflection is a whole other kettle of fish.

  9. #9
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    Quote Originally Posted by hardmtnbiker View Post
    I really like the look of the curved seat tube on hardtails and gravel frames. Iím starting to see this more and more and especially on metal frames Iím sure it helps create a more supple feel.
    I bought an Esker Hayduke but the small size has very little curve. Now Iím looking for a gravel frame and intend to build up as a fat tire rig with 650b wheels.
    Any suggestions?
    I ride XL frames and i'm a bit pudgy. The upside is i know all about seat tube flex. There is functionally nothing to be gained by a curve here. Using a small diameter tube is a theoretical benefit, and i can definitely feel the deflection offered by a maxed-out thin wall 400mm 27.2 post. I doubt you will, though.

    I prefer to use a straight seat tube with a forward offset at the bb, rather than a bent seat tube: it has nothing to do with comfort and more to do with aesthetics and cost. With custom- aligning the bend with the tire is a hassle.

    practical opinion- ignore this for a desired feature. If you're riding small frame 650b seek out non-oversize tubes and ideally a 27.2 seat tube. 25.4/28.6 front triangle ftw. Everything is stupidly overbuilt for you, no matter what you weigh. There are tubing deflection calculators online that are worth spending 45 minutes playing with. I'm a hobbyist with no engineering background, (i'm not comfortable offering authoritative advice) but i know you'll come to some very reasonable/radical conclusions.


    sorry for not answering your question.
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  10. #10
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    Iíll agree with others that a curved seat *tube* has little effect on frame compliance. However, the increased deflection of the seat *post* may be significant as the seatpost will have a more horizontal angle. Not just feel, but you can see a 27.2mm post flex with even a moderate sized rider.

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