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Thread: Seat Post 101

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    Junior Member Anamnesis's Avatar
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    Seat Post 101

    Can someone school me on set back vs straight seat post? Its time to buy a new seat post but I don't know enough about these designs and I'd like to make a reasonably informed choice.

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    Must... ride... more... Phil_gretz's Avatar
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    Quote Originally Posted by Anamnesis View Post
    Its time to buy a new seat post...
    Can you be more specific as to the reason you're looking for a new seatpost? Type of bike, recent riding history with regard to fit, what you're trying to correct/adjust, saddle specifics, etc...

    With this type of information, you'll get some great feedback. Typically, the amount of setback varies with the geometry of the frame's seattube angle, the frame size in proportion to the rider's ideal dimensions, the configuration of the saddle rails, and the desired fit characteristics the rider seeks. These can combine to give you a range (between saddle rail adjustment and setback) that will work for a particular bike.

    So, what bike is it and how does it fit now?

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    Yes, as Gretz gets at, it's not a matter of just picking a seat post design, it's a matter of getting the seat post you need to meet your needs. In addition to his questions, you should let us know where your current post clamps the seat rails and what design the post is. A pic would help too; if you're maxing out available rail with a setback post now, you won't be able to use a straight post without changing seat position. If you're changing anything else about the bike that'll play in, too.

    In general, though, a seat post is not what I'd consider a 'mission critical' component. Yes, depending on how much extension you've got and how you ride, one may be able to select a post material for added comfort; I find long extension Ti and carbon fiber more comfy for long rides than aluminum, but short rides on short extension posts doesn't make a difference, and any difference in any case can be muted by saddle selection.
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

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    coprolite fietsbob's Avatar
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    a straight seat post is 7/8" at the top. the rest depends on the seat tube ID its going in on the bike frame.

    you buy a saddle clip to fit on top of them, to mount the saddle..

    Kalloy makes those in most-all diameters .. low cost..

    start adding an integrated saddle rail mount, and the range starts at Zero.. it sits directly on top.
    Thomson is one of that type, to have a setback from directly on top they bend the post shaft.

    others design the head so the clamp mech is behind the seatpost centerline.. including Kalloy.
    Last edited by fietsbob; 12-05-13 at 01:24 PM.

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    Senior Member Looigi's Avatar
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    The saddle should be positioned properly with respect the crank with respect to your physiology and how you ride (AKA "fit"). Choose a seatpost that will allow the saddle to be positioned where it needs to be within the adjustment range of the saddles rails.

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    Junior Member Anamnesis's Avatar
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    Quote Originally Posted by chaadster View Post
    Yes, as Gretz gets at, it's not a matter of just picking a seat post design, it's a matter of getting the seat post you need to meet your needs. In addition to his questions, you should let us know where your current post clamps the seat rails and what design the post is. A pic would help too; if you're maxing out available rail with a setback post now, you won't be able to use a straight post without changing seat position. If you're changing anything else about the bike that'll play in, too.

    In general, though, a seat post is not what I'd consider a 'mission critical' component. Yes, depending on how much extension you've got and how you ride, one may be able to select a post material for added comfort; I find long extension Ti and carbon fiber more comfy for long rides than aluminum, but short rides on short extension posts doesn't make a difference, and any difference in any case can be muted by saddle selection.
    Thanks! No, I'm not just picking a design, quite the reverse, I've been looking into seat posts for a new build and realized that I literally do not know what's behind the engineering/design concept of a set back post and I really like to learn about what interests me.

    I am currently riding a Selle Anatomica Titanico saddle on a Campagnolo single bolt fluted seat post. I'm planning to use the Titanico on the new bike. I've borrowed a Paul Tall and Handsome which I have not yet used, but it's design is what led me to find out about seat posts and what I'd want to keep in mind for riding.

    So, other than more seat post information in general I'd like to be able to adjust the tilt (?) which is to say I want the saddle nose to point down a bit. I'm riding an early 1980s steel road bike with a 1x9 drive. This is my daily commuter. I ride 50-100 miles each week. Most days I'm riding hard on rough streets and dirt alleys in typically short bursts (15-20 minutes) with longer rides on more agreeable surfaces a couple of days a week. I'm just reading about bike fit so I'm adjusting saddle height and fore and aft position frequently (see photo for current positioning) and I don't have it dialed in. I'm 5'11" and the frame is 55cm, 700c.

    I'm looking for durability and more adjustability. And a handsome design wouldn't be too shabby. anything else I can tell you?

    thank you all for your replies!
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    coprolite fietsbob's Avatar
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    Another definition of setback starts from the Plumb bob vertical line thru the BB axis..

    Part of frame design..


    I'm looking for durability and more adjustability. And a handsome design wouldn't be too shabby.
    Riv Bike imports Nitto's Straight seatpost in 27.2 w 22.2 top... premium quality.

    Brompton Penta Clip is the best saddle clip Ever made , IMO.

    stepless through 360 degrees rotation, holds fast, 1 bolt. 90% aluminum.
    Last edited by fietsbob; 12-06-13 at 12:34 PM.

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    Anamnesis,

    Looking at your pic, I think you can see that a zero setback post would work for you, because if you imagine the clamp head directly atop the post, there'd be plenty of flat rail section to clamp to.

    As for the design and engineering question, I really don't think either design confers anything precious, and that they're merely different ways to get the saddle where it needs to be.

    In the old days, before the clamp was attached to the post, offset was the rule just because there needed to be room for the clamping bracket to be tightened onto the post. In the really old days, not only was offset common, but it was 'setforward,' with the seat cantilevered quite forward of the post.

    Really, when you look at vintage bikes, there was such a wide variety of designs and executions, that various and funky seatposts. I don'th think the modern setback design really popped up until the 60s, but I'm not sure. Similarly, the modern zero setback didn't really become popular until the '90s, I don't think.

    Nowadays, there's still plenty of choice, as you can find zero offset clamps on bent posts that achieve setback that way, all the way up through front offset clamps and forward bent posts favored by the triathlon an time trial disciplines. Again, none are about benefits of design beyond where it positions the saddle.

    VeloNews, not long ago, did a comparison test of seatpost vibration damping and other performance metrics. As I recall, it was not really possible to draw any conclusion as to whether setback or zero offset posts, as a virtue of those design elements alone, offered anything of distinction. The test did not address what I think are some of the most impotant variables in seatpost performance, namely extension and seat postion.

    The feature that's probably more important to you is fine tilt adjustment, or microadjustment. In my experience, two bolt (fore/aft) zero setback posts are easiest in this regard, because loosening one bolt and tightening the other allows infinte, easy, microadjustment. Thomson Elite post is an example of this type. However, there are tons of clamp designs that may work just as well, e.g. Kent Eriksen's Sweetpost, or Ritchey's SuperLogic 1 bolt.

    Typical 1 bolt setback head designs can be fussy since loosening to adjust tilt slops out the whole clamp and require two hands and some judiciously applied force to get moving, and a keen eye towards adjustment as tightening pulls down and can give more tilt than planned. I think your Paul design addresses that problem.

    As a final note, I dont think you've enough extension to discern post material difference, so you're free to choose on style!

    I hope thst helps!
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

  9. #9
    coprolite fietsbob's Avatar
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    Race Face Sumo, & the Thomson, &

    a USE (UK) spring/elastomer suspension* seat post are Zero setback.

    * [It's a rider weight adjustable, good one]


    FWIW, with a leather saddle like that or Brooks the Traditional 2-Bolt Campag posts were Fine..

    the <C> dog leg wrench had a 10mm hex on one end, for those Bolts,
    and an open end that fit the Brooks tension Nut, on the other.. for a Reason.
    Last edited by fietsbob; 12-06-13 at 04:14 PM.

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    Back in the olden days, seatposts came in one shape only. If you wanted to alter the fore/aft position of your saddle beyond the rails you needed a custom geometry frame with a different seat-tube angle.
    These days, you can get seatposts with a variety of laybacks from inline to way back and even some forward ones. Few people need resort to custom geometry frames to set their saddle with respect to pedal position.

    The starting point for pedal->saddle relation is Knee Over Pedal Spindle or KOPS. From this standard relation, you can adjust back and forward to suit your own body shape, power flexibility and position. More here.
    I prefer to note this relation by using [x,y] coordinates (cartesian) rather than include seat-tube angles (polar coordinates). I use the BB as [0,0]. By using cartesian coordinates, you can replicate most positions on most production frames of the correct size.

    How much layback do you need? Do you know your current riding position? Do you have a bike setup the way you like it at the moment?

    Inline posts are generally easier to adjust for level than trad single bolt clamps. Once you yank apart the two ridged surfaces, you loose the original position.
    Some posts have single forged construction, others are glued from several bits. Carbon posts can be made in one or glued from components.
    Ultralight posts seem to suffer more (or more public) failures than mid-range ones with thicker, but lower grade materials.
    Last edited by MichaelW; 12-06-13 at 12:13 PM.

  11. #11
    Senior Member JerrySTL's Avatar
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    If you have a set back seatpost now and the bike seems to fit you properly, look under the saddle. Is is slide forward on the rails a lot? In that case you might want to consider a straight post as that could put the clamp more towards the middle of the saddle. If it's already near the middle, go with something like what you already have.

    If you already have a straight seatpost and the saddle is slid way back, then maybe a set back seatpost might work better for you. Again, if it's already near the middle, don't mess with success.

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