Sep 11, 2003 10:06 AM
|What is the purpose of using a setback seatpost (other than the obvious fact that is puts your riding position further back)?
It seems to me that if you had a properly fitted frame, that you wouldn't need a setback to get properly positioned in relation to the pedals. So, is to correct a situation where stock frame geometries don't fit certain body types, and thus the need for the setback?
However, I can't imagine that the sole purpose of setback posts are to rectify improperly fitting frames. Can a custom builder then build a frame for these folks that wouldn't require a setback? (seems like I've seen plenty of custom frames with setback posts though)
Also, that are the drawbacks of running a setback. Seems like if your running a setback, your center of gravity would be behind where it was intended to be for that frame, thus affecting the handling of the bike.
I'm confused. Will someone please set me straight?
Sep 11, 2003 10:19 AM
|The issue with the setback is that the actual seattube angle has an effect on how the bike rides. Steeper seattube angles generally result in harsher rides, and tighter handling bikes. A "crit" bike (or a TT bike) is likely to have a steep seattube. More relaxed seattubes give a more plush ride, and are very common on touring bikes.
So the framebuilder would use the seattube angle to create a frame that rode the way you wanted it to (as opposed to the one that fit you perfectly, without adjustment), and rely on the seatpost setback and saddle rail position to move you into the right position.
|re: Setback seatposts...........why?||03Vortex|
Sep 11, 2003 10:24 AM
|Any stock frame may need some fine tuning to get it dialed in right based on what an individual wants. A setback post will allow you to push the saddle back whether you need to based on body dimensions AND/OR you desire to in order to gain more climbing leverage. The post also allows you then to center your saddle on the rails. Also, any fore/aft adjustment to saddle also impacts reach and needed stem length.
I have s stock frame and use a Easton setback post. I suppose a custom frame should enable you not to need a setback post unless you wanted to slide it back for the climbing reasons noted above.
|re: Setback seatposts...........why?||gtx|
Sep 11, 2003 10:33 AM
|most bike frames are designed to be used with a seatpost with some setback--ie your "standard" Campy post, a standard which has been around since at least the 60s or 70s. Richard Sachs says "When I see a rider on one of my bikes and the saddle is positioned in the center of the rails, I know I've done my job correctly."--and I know he is referring to Campy setback posts. One possible exception seems to be IF, since they use slightly more relaxed seat tube angles than many builders, and tend to picture their bikes built up with Thomson no-setback posts. Maybe this is because of their non-standard 26.8 seatpost diameter? Maybe someone can answer how the setback post became the standard--aesthetics, early clamp designs?|
|agree many of todays "non-setback" posts still have setback (nm)||Frith|
Sep 11, 2003 12:40 PM
|It's a way of adjusting the seat tube angle without.....||MR_GRUMPY|
Sep 11, 2003 10:53 AM
|getting a custom frame. Another thing, is that peoples bodies change after riding a few years. You may find that you are doing mostly road races and need to be farther back. A setback seatpost will prevent you from having to but a new custom frame.|
|Why would you want set back for a road race?||Kristin|
Sep 11, 2003 11:01 AM
|Isn't set back considered "relaxed" geometry? I would think someone racing would not want a slacker STA.|
|Why would you want set back for a road race?||sievers11|
Sep 11, 2003 11:10 AM
|Puts you knee farther back over the center of your horozontal front peadle axel. This is a more powerful position when climbing, it will also allow you to comfortably ride in a more powerfull position on the "tops" with will also open up your chest and allow you to get in more O2. Because you are not climing so much in a Crit (if there are hill they are usually sprints) the forward sprinter position is better, but road racing is usually decided on the hills|
|STA should always be slacker on a RR frame compaired||MR_GRUMPY|
Sep 11, 2003 11:18 AM
|to a Crit frame. Crit frames are often like Track frames. 74,75 or even 76 deg STA. Because road races are much longer, you need to be more comfortable. 73 or even 72 deg is common.|
Sep 11, 2003 11:00 AM
|DeBernardi Aelle stock frame: $326
Set back seat post: $74
Total cost: $400
Custom Gunnar frame: $1200
Set back seat post: $0
Total cost: $1200
|thats a loaded answer||sievers11|
Sep 11, 2003 11:14 AM
|You still have to get a seat post for the Gunnar.
If you look around you can find varying geometrys to allow for a centered post. Stock isn't seat angle isn't always 73, it can vary from 72-74.
|Yes.......That's the answer.||MR_GRUMPY|
Sep 11, 2003 11:24 AM
|Sometimes you just have to "fudge" the frame, a little, to make it fit.
That is the reason I bought a "stock" Gunnar frame for $600 (It's now $650)
Sep 11, 2003 4:14 PM
From one bean-counter to another :
That answer is so accountanty!!
Accurate but geez, how bean counterish!!
Of course I just spent my kids college fund on another Bike I don't REALLY need.
|Shorter Chain Stays and Fabrication||sievers11|
Sep 11, 2003 11:06 AM
|Short chain stay = stiff acceleration
Short chain stay = vertical seat tube
Short chain stay = set back post or else bend the seat tube around the wheel.
It should also be noted about the practicality of fabricating a seat post, your "Classic Campy" design is also a very simple solution. Set it back and then you can have room to put the single 6 mm bolt in place. Notice most of the centered (non-set back) posts have multiple and rather complicated clamping mechanisms.
|Both Campy, and DuraAce seatposts are medium setback||MR_GRUMPY|
Sep 11, 2003 11:31 AM
|seatposts that most people can use. If you have extra short or long legs, you may need something different. If you have a set-back seatpost, like the Easton, you can still use the bike for Crits. You just have to be "on the rivet" most of the time.|
Sep 11, 2003 11:35 AM
|Road bike seatposts have been traditionally built with the front of the seat rail clamp located approximately along the center of the post for more than 20 years. This design allows seat tube angles as steep as 74-75 degrees. Steeper STA permits the chainstays (and wheelbase) to be shorter, whithout the tire touching the seat tube. That's about all there is to it.
Setback seatposts are the standard, not something used to correct a fit problem. There are no drawbacks to using a setback seatpost. There is also no "intended" center of gravity for a stock frame. Unless you have a custom frame built with special length chainstays, you really have no control over weight balance, unless you are willing to compromise your KOP position for the sake of weight balance. Most riders adjust the saddle and stem for comfort and pedaling efficiency and the weight balance is what it is.
If you use a straight up seatpost, like a Thomson, you would need to reduce the STA by 1.5-2.0 degrees to achieve the same rider position, since the front of the seat tube clamp is 2cm ahead of the seatpost centerline. That's why it's rare for a straight-up seatpost to work on a stock frame. Most are designed around a traditional "setback" seatpost.
A frame can be built to fit exactly the same with either design. There would be no difference in weight balance and an imperceptable difference in ride.
|re: Setback seatposts...........why?||russw19|
Sep 11, 2003 11:45 AM
|Many older seatposts had the setback built into them. The clamp design sat quite far behind the center axis of the actual post. Newer designs are all about weight, so there is not as much set back from the center axis of the post because of newer and lighter clamping designs. If you look at a couple posts that offer setback styles and regular styles you can actually see that "non-setback" posts are really pretty far forward posts. Look at the Moots and Thompson posts in particular. They both clamp pretty much directly over the post's center axis. They both offer laid back designs as well and those posts move the clamp back about 30mm behind the center axis of the post. This position is more in line with where traditional posts of the 70's and 80's clamped seats. Since the weight revolution started, many posts started to move the clamping mechanism closer to the center of the post as they tried to make lighter posts. Perfect examples of this would be the Syncros posts of the 90's as well as Ringle posts of the same era. Whereas if you look at a mid 80's Campy Record post, you can see how far back that post sat. Another factor is that in order to make seats lighter, many companies have adopted a short rail system that doesn't give as much room for adjusting the saddle fore and aft on a post.
|More confusion.....setback vs. layback||TWD|
Sep 11, 2003 12:05 PM
Now you've all got me even more confuses. I've heard the term "setback" and "layback" seatpost used interchangeably. Are they the same thing?
The type of post I'm trying to figure out are the ones that have a visible bend in the post itself, not just a clamp that centers farther back.
In the case of the Thomson posts, is their "bent" post version basically a way to move the clamp position further back without adding extra material weight to the clamp itself?
|The thompson "layback" post offer very little setback,||MR_GRUMPY|
Sep 11, 2003 12:13 PM
|but they are better than the standard Thompson.|
|Amount of setback...||Fez|
Sep 11, 2003 12:25 PM
|Seatposts with standard setback are such that the front of the clamp rail intersects the centerline of the post.
Take a straight edge along the centerline of the Thomson post BELOW the bend and see if the front of the clamp rail intersects that line.
|Observation: Absolutely NO Rhyme or Reason...||Fez|
Sep 11, 2003 12:17 PM
|Lots of great responses above from the likes of TJ, Mr. Grumpy, C-40, Russ, etc.
HOWEVER, the manufacturers and retailers seem to be far less enlightened. They seem to put far less thought, from a fit perspective. A few examples:
1) Colorado Cyclist used to offer traditional seatposts (Shimano, Campy, Am Classic) in their kits, then later on started offering Thomson straight posts. I hope they are offering the setback version as well.
2) Lemond offers a traditional post on some bikes, and a Thomson straight post other bikes. They are the same geometry frame, but different spec'd model. Same thing with Trek, Cannondale, Specialized and Litespeed.
There appears to be absolutely no rhyme or reason as to the seatpost they offer. It seems to be more of a "business" decision than a "fit" decision.
In an industry where fit DOES matter, there is a lot of inconsistency in how manufacturers and retailers specify seatposts.
|It's because Thompson posts look cool||MR_GRUMPY|
Sep 11, 2003 6:12 PM
|The Easton post looks kinda' weird, so they spec a Thompson instead. That is the reason that Easton came out with their carbon post. People will buy carbon, even if it is carbon covered dog s**t.|
|Saddle rail length||Steve Bailey|
Sep 11, 2003 1:22 PM
|In addition to the existing posts mentioning how manufacturers "assume" a typical neutral setback, note also that not every saddle has rails of identical length. And I can say that I'm alway's amazed at how different a very minor change of fore/aft position of the saddle feels in terms of reach. Thus it's useful to have posts with zero setback, or neutral, or even some with a lot - such as the Easton or CLB posts.
As per saddles, when I switched to Brooks B17's, the 2nd thing I became aware of (the first was how comfortable the saddle was) is that the rails are shorter then the typical titanium ass hatchet and that my reach to the h-bar's had shortened. Getting my body back where it belonged meant a post (Easton on one bike, CLB on another) with more then typical setback.
|I had the same result. Brooks has shorter rails. nm||Len J|
Sep 11, 2003 3:07 PM
Sep 12, 2003 5:39 AM
|Personally, I don't see how anyone achieves proper fit with a straight-up post like a Thompson. It all goes to show that we're all different. My bikes both have seatposts with a fair amount of setback, Campy Chorus and another one I can't remember the make of. I tried to put a Brooks Pro saddle on my bikes (which both have slack 72.5 seat tube angles) and still couldn't move the saddle far enough back for proper fit. The rails on Brooks saddles are very short and/or positioned differently than most saddles. If I tried to use a Brooks saddle with a Thomson post, I would be hanging over the handlebar and front wheel. Another reason for a setback style post, as others mentioned, is a frame with steep seat tube angles. My Gios frame has a 74 seat tube angle and the only way to position the saddle properly is with a setback post.|
|here's why (I'm surprised no one got it yet)||ET|
Sep 12, 2003 11:12 AM
|A post with setback allows one to ride a smaller (and of course lighter) frame (with slightly steeper seat tube angle than otherwise) by getting him back to the same effective position he would be on the larger frame. There is no real penalty, so it is a good idea. In addition, a post with setback should take out a tad more road shock than a straight one.
It does not seem to depend on seat tube angle; Lemond, for example, still includes setback posts with their very slack-angled frame sizes.