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  1. #1
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    setback seatpost?

    What are the pros and cons of a setback seatpost versus straight seatpost? Context is aggressive trail riding.

  2. #2
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    Quote Originally Posted by weekendthrasher View Post
    What are the pros and cons of a setback seatpost versus straight seatpost? Context is aggressive trail riding.
    Setback seatpost should be used for fine tuning reach or fit in some case you are in between size. If the context is aggressive riding then an adjustable seatpost would be a much better choice

  3. #3
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    It really doesn't matter a whole lot as long as the fit is right. You can use post setback to fine tune bike fit - if your bike is a bit too long for you to get right behind the seat on steep descents then a post with an inline clamp can help. If your bike feels a bit too short, a setback post can move you back a bit.
    Less isn't MOAR

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    People often overlook the position of their knees relative to the pedals. You generate the most power when the ball of your knee is directly above the ball of your foot/center of pedal. Change the fore/aft position of your saddle changes leg position as well as reach.
    ...but of course personal preference and comfort is always a priority

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    Also depends what kind of bike it's going on and the seatpost material. I am running a titanium layback on a hardtail and provides a lot of cushion, especially since my seat tube is built really slack too

  6. #6
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    Shenny's answer is the most accurate so far. In order to pedal efficiently you need to have your saddle at the proper height and adjusted fore/aft so that your knee is properly located over the pedal. You can do searches on bike fit to find out exactly where your saddle needs to be placed - search for KOPS (knee over pedal spindle) for a good starting point on fit.

    Since the saddle needs to be correctly located related to he pedals, different seat post offsets are needed to properly locate the saddle. Your femur length and seat tube angle of the frame will determine if a straight or set-back post is needed (or you may be able to use either). Generally, people with longer femurs will need a set-back post. Also if your frame has a steep seat tube angle (73 or 74 degrees) a setback seat post may be needed (unless you have shorter than average femurs)

    Different seat posts have different amounts of set-back. Depending on your frame, saddle height, and femur length you may need to look for a post with a specific off-set.
    Last edited by laffeaux; 11-25-2011 at 02:52 PM.
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    Quote Originally Posted by shenny88 View Post
    You generate the most power when the ball of your knee is directly above the ball of your foot/center of pedal.
    Nonsense.

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    I'm 5'6" and am torn between getting a size 16 or 17 frame. Is it safe to assume that if I'll get the 16, I'll get a set back seat post and if I get a 17, I'll get a zero set back seat post? I'm asking this cause I'm going to order a frame with the seat post. Our LBS here doesn't have the seat post size that fits the frame's seat tube.

  9. #9
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    Quote Originally Posted by Chonggo View Post
    I'm 5'6" and am torn between getting a size 16 or 17 frame. Is it safe to assume that if I'll get the 16, I'll get a set back seat post and if I get a 17, I'll get a zero set back seat post? I'm asking this cause I'm going to order a frame with the seat post. Our LBS here doesn't have the seat post size that fits the frame's seat tube.
    The frame size does not effect the saddle position. If the seat tube angle is the same, once the seat post is extended to the proper length the saddle will be in the same place. If the seat tube angle is different, then the type of post may differ.

    A smaller frame (with the same STA) will require a longer stem, and possible more spacers under the stem to raise the handlebar.

    Moving the saddle rearward does not make a smaller bike fit you. It puts you in a different pedaling position.
    Each bicycle owned exponentially increases the probability that none is working correctly.

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    Quote Originally Posted by Chonggo View Post
    I'm 5'6" and am torn between getting a size 16 or 17 frame. Is it safe to assume that if I'll get the 16, I'll get a set back seat post and if I get a 17, I'll get a zero set back seat post? I'm asking this cause I'm going to order a frame with the seat post. Our LBS here doesn't have the seat post size that fits the frame's seat tube.
    Is it the same brand? HT or FS, it seems odd that a company would make one at 16" and 17" You won't know about the fit til you test ride it, look for a comfortable cockpit, you should be able to move around.

    Reach and TT play bigger role than having dead-center-perfect over the pedals. If I'm on my XC HT then I'd like to be over the pedal more but on my trail bike I'm fine with being a bit behind the BB. On my trail bikes if I'm right over my BB it'd be too far forward.

  11. #11
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    Quote Originally Posted by laffeaux View Post
    The frame size does not effect the saddle position. If the seat tube angle is the same, once the seat post is extended to the proper length the saddle will be in the same place. If the seat tube angle is different, then the type of post may differ.

    A smaller frame (with the same STA) will require a longer stem, and possible more spacers under the stem to raise the handlebar.
    Agreed. Effective seat tube angle will determine the setback needed.

    Quote Originally Posted by laffeaux View Post
    Moving the saddle rearward does not make a smaller bike fit you. It puts you in a different pedaling position.
    If you rotate your body backwards (about the pedals) while keeping all your body angles the same, you will be further back without altering your pedaling mechanics. The results will be a rearward saddle that's a little bit lower and tilted a little nose up. It will also needs a shorter TT or shorter stem. Done properly, you can fit a smaller bike without messing with pedaling mechanics.

  12. #12
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    Can't agree Craig, either about the body rotation or the knee over pedal, though that is just a starting point.

    There seems to be an optimal leg extension (roughly a slightly bent knee with a level foot) for power and comfort. That is fixed for each rider regardless of bike. It effects seat height. Relative patella over spindle (again roughly) presents force in a manner managble by the knee and lower leg. This defines the seat fore and aft position. Unless your leg chages size, that is a fixed postion, too. Those two fixed values determine seat position.

    With considerations for fitness, athleticism, riding style, and bike type, general seat position doesn't change very much. A body and leg rotation backward removes some of the contribution of gravity in the pedal stroke, resulting in power loss. Body and leg rotating forward causes pushing backwards. Both changes take you away from good balance over the bottom bracket and result in a loss of power. As such it does effect pedalling mechanics.

    I would be interested to hear your mechanical explaination of your point of view.
    Last edited by Berkeley Mike; 11-25-2011 at 09:16 PM.
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    Quote Originally Posted by Berkeley Mike View Post
    Relative patella over spindle (again roughly) presents force in a manner managble by the knee and lower leg. This defines the seat fore and aft position. Unless your leg chages size, that is a fixed postion, too. Those two fixed values determine seat position.
    No, they don't. A recumbent rider can generate just as much power as an upright rider and he does not come close to "knee over pedal". Accepting that there is an optimal set of leg angles for power production, as you suggest, there are still an infinite number of positions that allow for that, only one of which is "knee over pedal".

    Quote Originally Posted by Berkeley Mike View Post
    With considerations for fitness, athleticism, riding style, and bike type, general seat position doesn't change very much. A body and leg rotation backward removes some of the contribution of gravity in the pedal stroke, resulting in power loss.
    Like to see proof of that.

    Quote Originally Posted by Berkeley Mike View Post
    Body and leg rotating forward causes pushing backwards. Both changes take you away from good balance over the bottom bracket and result in a loss of power.
    Like to see proof of that.

    Quote Originally Posted by Berkeley Mike View Post
    I would be interested to hear your mechanical explaination of your point of view.
    Explanation of what?

    See this paper, in particular figure 2, to see what I'm talking about then read the results to see that you are wrong to say that power or mechanics are effected by rotation. This study focused on recumbent riding positions compared to upright, an extreme difference, yet power was uneffected. Furthermore, an adult can effectively move backward on a saddle 20-30mm with only a degree or two of rotation, underscoring the absurdity of any "gravity" effects.

    Jeff Jones practices a relative pronounced rearward rotation in his approach to fit, yet riders of his bikes, crazy though they may be , would not describe their power output as compromised (nor should they). Knee over pedal is a common and effective approach to fit, but there is nothing magic about it and it is not the only way that works. There is nothing wrong with it, either, if that's what a rider likes. I agree with mimi, different styles of bikes and riding can legitimately effect where the knee is relative to the pedal. It's totally appropriate.

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    Quote Originally Posted by craigsj View Post
    No, they don't. A recumbent rider can generate just as much power as an upright rider and he does not come close to "knee over pedal". Accepting that there is an optimal set of leg angles for power production, as you suggest, there are still an infinite number of positions that allow for that, only one of which is "knee over pedal".

    See this paper, in particular figure 2, to see what I'm talking about then read the results to see that you are wrong to say that power or mechanics are effected by rotation. This study focused on recumbent riding positions compared to upright, an extreme difference, yet power was uneffected. Furthermore, an adult can effectively move backward on a saddle 20-30mm with only a degree or two of rotation, underscoring the absurdity of any "gravity" effects.

    Jeff Jones practices a relative pronounced rearward rotation in his approach to fit, yet riders of his bikes, crazy though they may be , would not describe their power output as compromised (nor should they). Knee over pedal is a common and effective approach to fit, but there is nothing magic about it and it is not the only way that works. There is nothing wrong with it, either, if that's what a rider likes. I agree with mimi, different styles of bikes and riding can legitimately effect where the knee is relative to the pedal. It's totally appropriate.
    I agree, also about crazy Jeff Jones too I'm planing to get the spaceframe after a test ride it's wicked fun, steel not ti but who cares.


    Not too long ago I got to test ride "the ride" quite typical of a cruiser geometry very relax and comfortable but this one do not have to sacrifice the power delivery as I can extend my leg. I was quite impress, not so much fun going up the steep hill but I just grind my way up without any problems.

  15. #15
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    Quote Originally Posted by craigsj View Post
    No, they don't. A recumbent rider can generate just as much power as an upright rider and he does not come close to "knee over pedal". Accepting that there is an optimal set of leg angles for power production, as you suggest, there are still an infinite number of positions that allow for that, only one of which is "knee over pedal".
    A recumbent rider also has a backrest to push against.

  16. #16
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    Quote Originally Posted by craigsj View Post
    No, they don't. A recumbent rider can generate just as much power as an upright rider and he does not come close to "knee over pedal". Accepting that there is an optimal set of leg angles for power production, as you suggest, there are still an infinite number of positions that allow for that, only one of which is "knee over pedal".


    Like to see proof of that.


    Like to see proof of that.


    Explanation of what?

    See this paper, in particular figure 2, to see what I'm talking about then read the results to see that you are wrong to say that power or mechanics are effected by rotation. This study focused on recumbent riding positions compared to upright, an extreme difference, yet power was uneffected. Furthermore, an adult can effectively move backward on a saddle 20-30mm with only a degree or two of rotation, underscoring the absurdity of any "gravity" effects.

    Jeff Jones practices a relative pronounced rearward rotation in his approach to fit, yet riders of his bikes, crazy though they may be , would not describe their power output as compromised (nor should they). Knee over pedal is a common and effective approach to fit, but there is nothing magic about it and it is not the only way that works. There is nothing wrong with it, either, if that's what a rider likes. I agree with mimi, different styles of bikes and riding can legitimately effect where the knee is relative to the pedal. It's totally appropriate.
    I'm not sure about "experts." Further, recumbants have a different leverage and don't use knees the way traditional riders do; it is much closer to walking. I'm not sure I can agree that they produce as much power as someone aided by their body weight above the pedals. In fairnesss, my limited experience with recumbant riders is a sample perhaps not as advanced as yours; we just sorta blow by them with little thought.

    People have lots of ideas about different kinds of fit. I've trained riders and racers for 13 years and fit them all for optimal power and handling. I have also been fortunate to have the support of some pretty skilled people in the business and my fits are seldom off by very much. Several of my fits were followed by computer aided fits (we got a very generous price for the team) and the difference wasn't worth mentioning. I don't have problems with stress induced injuries and my riders stay healthy. So "experts?"

    All that said I am working with XC racers and the position we use for riding 4 days a week and racing may not be for just anyone. It is hard to argue with something which works so demonstrably well for so many riders over so many years.

    Set back seatposts? Never seen one with this group or the 10 other teams I have worked with. I don't know what else to tell you.
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  17. #17
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    Quote Originally Posted by mimi1885 View Post
    I agree, also about crazy Jeff Jones too I'm planing to get the spaceframe after a test ride it's wicked fun, steel not ti but who cares.


    Not too long ago I got to test ride "the ride" quite typical of a cruiser geometry very relax and comfortable but this one do not have to sacrifice the power delivery as I can extend my leg. I was quite impress, not so much fun going up the steep hill but I just grind my way up without any problems.
    I have to see a picture of someone riding one of these. I'll bet you the setback seat post is an accomodation to this specially designed frame and that the rider will have their patella close to over the spindle. One of my custom Bike and Wheel builders creates bikes like that and that is how they all end up.

    As I look at the initial post by the OP they are not specific about what kind of bike they ride, whther they are looking for a handling edge, or correcting a badly fit bike. "Agressive trail riding" tells very little and makes the question hard to address. This is all too general. Lack of complete info concerning a question is common here and responses often end up being at loggerheads.
    Last edited by Berkeley Mike; 11-26-2011 at 10:08 AM.
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  18. #18
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    Quote Originally Posted by craigsj View Post
    Agreed. Effective seat tube angle will determine the setback needed.
    So will a 72.5 degree seat angle require a set back seat post?

  19. #19
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    Please don't respond with any hostility but, is anyone who has responded thus far to this thread a certified Retul fitter??? I think this is the person I would want to add to this were it my query. I mean, years of experience and learning from being around the industry is great but, someone who actually performs this work as a source of livelihood and does so based on education in the area would be a valuable add to the thread.
    My two cents!!

    And, if you must flame my post...STFU!!!!!!
    If you don't like the way I ride, stay on the road!!!

  20. #20
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    Quote Originally Posted by Chonggo View Post
    So will a 72.5 degree seat angle require a set back seat post?
    It depends on the length of your femur. For me, I would be fine with a either a straight or set-back post with a 72.5 degree STA. With a post with moderate setback (i.e. Thomson) the saddle would be more centered on it's rails for my body dimensions.

    Compare your current bike setup (assuming you are correctly fit to the bike) to any new frames.
    Each bicycle owned exponentially increases the probability that none is working correctly.

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    Sorry, I meant size 15 or 17. It's a hard tail and has a 72.5 degree STA.

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