# The advantages of zero set back...



## Elfstone (Jun 27, 2006)

Hey people, I'm having a road bike custom made and I mentioned I wanted to use a Thomson Elite seat post. At the time I didn't know that the Thomson came with a zero setback and I didn't know that Thomson made a Elite Setback seat post too.

Well, the person building my frame designed the frame around a zero setback seat post. What are the advantages or disadvantages of having traditional style road bike with zero setback. The builder is going to start cutting the tubes in two weeks.

From what I've been able to gather so far, is that setback works better for road bike and zero setback works better for track and time trial bikes.

I'd really be most grateful for some feedback on the pros and cons of zero setback and setback seat post on a traditional style road bike frame, thanks.

Peace


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## rx-79g (Sep 14, 2010)

"Normal" frame geometry assumes a certain amount of setback. Zero setback posts would be useful to those with unusual leg proportions. Their popularity right now has more to do with how they look and how little they weigh than anything grounded in the reality of fit. I think the first seatposts of this variety were for MTBs.

I would have your frame design changed to a standard set back seatpost, if it were me. The weirder your custom frame geometry is, the harder it is going to be to sell it if you don't care for it.


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## ICEAXE (Mar 13, 2003)

What kind of seat angle do you prefer? How much handle bar drop do you use? Generally speaking the lower you get on the front of the bike, the steeper the seat angle has to be.


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## DaveT (Feb 12, 2004)

You need to talk to your builder about this. There is no advantage or disadvantage to either style seatpost, they merely allow you to set your saddle where it should be. A bike shouldn't be designed around a seatpost, it should be designed around you! If your builder is experienced, he will know far more than any of us here. If he's good, listen to him.


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## laffeaux (Dec 12, 2001)

For me, and my body proportions, a non-setback post means that I need to have a seat tube angle of 72 degrees or less. A set-back post allows me to ride frames with 73 or 74 degree seat tube angle.

Your builder may change the seat tube angle on your frame based on what post you chose to go with.


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## stevesbike (Jun 3, 2002)

tail wagging dog when a builder chooses angles based on seatpost preference... choose geometry then figure out what seatpost to use


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## Hank Stamper (Sep 9, 2009)

No advantage or disadvantage when talking about a custom frame built around a seat post.

With stock frames you might be able to split hairs and talk about body weight distribution and how that impacts handling but even that's generally not going to be a difference that actually matters.


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## PJ352 (Dec 5, 2007)

My first thought is that I'm surprised a builder would design a frame around a zero setback seat post, unless he's making some assumptions. Either way, it doesn't instill confidence. 

I'd contact him and explain what your intended use(s) are. Unless there are reasons to go with a no setback post (anatomy/ specific use), I wouldn't do it.


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## Len J (Jan 28, 2004)

For the same body proportions...... and the same Fit on a bike

A non-setback seatpost will require a slacker seat tube angle compared to a setback seatpost to get the clamp in the same place on the seat. This can affect the chainstay length required for clearance and ultimatly the handling of the bike.

As someone on another board has said.....everything is interrelated.

IME

Len


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## Frith (Oct 3, 2002)

*Since nobody has mentioned the obvious yet.*

It's to do with fit. Not to do with the type of riding you're doing.

There is a particular saddle fore/aft position relative to the bottom bracket that will give you the most efficiency and comfort. 
This saddle position can be achieved and is affected by a few things
1. Where on saddle rails you clamp the seatpost.
2. Seatpost setback. (besides the two extremes offered by thompson there are lots of seat posts out there with setback ranging between the two)
3. Seat tube angle

Generally ideal saddle fore/aft is obtained by some combination of the above factors. You don't, for instance, use a set back seat post and then slam the saddle all the way forward on the rails nor do you design a custom frame with steep angles and then stick a set back post on there to compensate just as you wouldn't design a frame with slack angles and set a zero set back post on there to compensate.

For myself I would choose the zero setback post but that's more due to knowing my proportions and knowing that I generally need to be a bit further forward on bikes with fairly standard angles.

Your builder may be building around the zero set back post because with your proportions this option allows him to build with more regular seat tube angles. Or you builder just doesn't know that thompson offers the seatpost in a set back. You really need to speak to him to iron that out.

You need to get it out of your head that the setback has anything to do with functional use of the bike... It is purely about fit.


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## PlatyPius (Feb 1, 2009)

Me, I have to use a zero-offset on a normal road bike. My femur length is very short. With a set-back/offset seatpost, I ride on the nose of the saddle.


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## ZoSoSwiM (Mar 7, 2008)

I picked up a zero offset because I needed my saddle moved forward slightly and I didn't want to max out the forward slide of my saddle rails. Other than that I like how it looks.


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## c_kyle (May 28, 2010)

So, if a zero-set-back post will position the saddle where I need it to be, is there any reason to still use a set-back post?


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## appleSSeed (Nov 17, 2005)

^no

of course not


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## PJ352 (Dec 5, 2007)

Frith said:


> *It's to do with fit. Not to do with the type of riding you're doing*.
> ... It is purely about fit.


No argument with the fit issues you covered, but disagree that_ type _of riding doesn't enter into this. When correctly set up, a tri/ TT rider is positioned differently than a road rider, necessitating changes to fit/ weight distribution. 

Either way, fit requirements (of the rider) need to be met, but they're met in differing ways.


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## PJ352 (Dec 5, 2007)

c_kyle said:


> So, if a zero-set-back post will position the saddle where I need it to be, is there any reason to still use a set-back post?


No, but it _may_ be an indicaton that the bikes geo isn't ideal for you.


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## krisdrum (Oct 29, 2007)

Frith said:


> 2. Seatpost setback. (besides the two extremes offered by thompson there are lots of seat posts out there with setback ranging between the two)


The Thomson stuff is hardly "extreme", the setback post I think has 16mm of setback. Most of the Ritchey and Easton lines have 20-25mm. As setback posts go, the Thomson is hardly on the extreme side.


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## simonaway427 (Jul 12, 2010)

There are a number of theories as to advantages/disadvantage. One that many forget to mention is aero position.

The further back your saddle is, the lower your saddle height must be in order to maintain optimal leg extension. Moving your saddle forward allows you to run a higher saddle height, which in turn, allows you to run a larger saddle/bar drop - allowing you to get lower in your aero position (assuming you have the flexibility to do so).

This is one of the reasons why TT bikes have the steeper STA, they can run higher saddle heights and optimize their aero position.


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## CougarTrek (May 5, 2008)

There are advantages and disadvantages to various positionings on a bike.

Seatpost setback (or lack thereof) is simply a way to achieve those various positionings (especially on stock bikes where you don't have the luxury of requesting a certain seat tube angle and various other geometry considerations).

If the bike has been properly designed to match your geometry and riding style with a zero-setback Thompson in mind there should be zero issues.

I have a custom Cross bike that is designed this way that I could probably never ride 100% in the right position if I put a setback post on it, but I have no intentions of ever doing so.


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## krisdrum (Oct 29, 2007)

simonaway427 said:


> There are a number of theories as to advantages/disadvantage. One that many forget to mention is aero position.
> 
> The further back your saddle is, the lower your saddle height must be in order to maintain optimal leg extension. Moving your saddle forward allows you to run a higher saddle height, which in turn, allows you to run a larger saddle/bar drop - allowing you to get lower in your aero position (assuming you have the flexibility to do so).
> 
> This is one of the reasons why TT bikes have the steeper STA, they can run higher saddle heights and optimize their aero position.


Huh? Sorry, may be dense today, but I am trying to visualize this and just am not getting it. How does setback have anything to do with saddle height? The way I am envisioning it (and am totally open to correction), is we are basically rotating around the BB. Seat tube angle in conjunction with setback determines where we sit in relationship to the BB. But optimal saddle height is optimal saddle height as is determined by your physiology. As you rotate around the BB, the distance between BB and saddle top remain the same, they are just oriented at a different angle. Seat tube angle and saddle setback don't change your leg length, do they?

I agree that steeper seat tube angles "appear" to have a higher saddle position, but I am not convinced that a slacker seat tube angle would necessitate lowering your saddle height to get the same knee bend at the bottom of the pedal stroke.


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## simonaway427 (Jul 12, 2010)

krisdrum said:


> Huh? Sorry, may be dense today, but I am trying to visualize this and just am not getting it. How does setback have anything to do with saddle height? The way I am envisioning it (and am totally open to correction), is we are basically rotating around the BB. Seat tube angle in conjunction with setback determines where we sit in relationship to the BB. But optimal saddle height is optimal saddle height as is determined by your physiology. As you rotate around the BB, the distance between BB and saddle top remain the same, they are just oriented at a different angle. Seat tube angle and saddle setback don't change your leg length, do they?
> 
> I agree that steeper seat tube angles "appear" to have a higher saddle position, but I am not convinced that a slacker seat tube angle would necessitate lowering your saddle height to get the same knee bend at the bottom of the pedal stroke.


We aren't talking about seat tube angles here, we are talking about setback and saddle position. With the STA fixed, you are NOT rotating around the bottom braket when the setback is changed. When you slide your seat rearward, you are increasing the distance between the saddle and the BB - and vice versa when you slide the seat forward. Try it - just make sure you mark your seat rails first


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## PJ352 (Dec 5, 2007)

simonaway427 said:


> There are a number of theories as to advantages/disadvantage. One that many forget to mention is aero position.
> 
> The further back your saddle is, the lower your saddle height must be in order to maintain optimal leg extension. Moving your saddle forward allows you to run a higher saddle height, which in turn, *allows you to run a larger saddle/bar drop *- allowing you to get lower in your aero position (assuming you have the flexibility to do so).
> 
> This is one of the reasons why TT bikes have the steeper STA, they can run higher saddle heights and optimize their aero position.


IMO, this is a stretch. While it's true that moving a saddle rearward will require a slight adjustment (downward) in saddle height, the amount in real world terms will hardly make the rider more aero. As an example, for a 1cm fore/ aft adjustment, a rider _may_ have to readjust their saddle height about 2-3mm's, making any saddle to bar drop change the same. 

FWIW, TT bikes use a top tube that is usually a couple of centimeters shorter to allow the use of an adequate stem length when riding on aerobars. The fact that STA is steeper is secondary.


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## c_kyle (May 28, 2010)

PJ352 said:


> No, but it _may_ be an indicaton that the bikes geo isn't ideal for you.


I am pretty proportionate, but am short, 5'5". The 49cm Tarmac feels good with a setback seatpost. When I ran a straight edge parallel to the seattube, it was almost in the middle of the saddle rails. So, I figured a zero set back post would work, and it's lighter. With a zero set back post, the clamp is forward of center on the saddle rails.

I'm not sure if a short inseam or short femur length would make a difference or not.


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## appleSSeed (Nov 17, 2005)

It's just a seatpost afterall.


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## c_kyle (May 28, 2010)

appleSSeed said:


> It's just a seatpost afterall.


It is not "just" a seatpost, afterall.


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## PJ352 (Dec 5, 2007)

c_kyle said:


> I am pretty proportionate, but am short, 5'5". *The 49cm Tarmac feels good with a setback seatpost. When I ran a straight edge parallel to the seattube, it was almost in the middle of the saddle rails.* So, I figured a zero set back post would work, and it's lighter. With a zero set back post, the clamp is forward of center on the saddle rails.


Then assuming your setback/ KOPS has already been set to your physical requirements, there's no need for a zero setback post.


c_kyle said:
 

> I'm not sure if a short inseam or short femur length would make a difference or not.


Assuming bike geo is correct for the rider, short inseam, no. Short femur, possibly. But you said you're proportionate and your saddle position bears this out, so IMO you should stay with your current post.


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## rx-79g (Sep 14, 2010)

simonaway427 said:


> There are a number of theories as to advantages/disadvantage. One that many forget to mention is aero position.
> 
> The further back your saddle is, the lower your saddle height must be in order to maintain optimal leg extension. Moving your saddle forward allows you to run a higher saddle height, which in turn, allows you to run a larger saddle/bar drop - allowing you to get lower in your aero position (assuming you have the flexibility to do so).
> 
> This is one of the reasons why TT bikes have the steeper STA, they can run higher saddle heights and optimize their aero position.


Posts like this reflect a certain relativism about saddle position that misses the point.

Having the correct saddle height AND setback for you saddle is for you HEALTH. Height makes sure you don't damage your knees, and setback helps keep you sitting on your sit bones, rather than you prostate and other soft tissues.

Triathletes make a rather radical compromise "sitting" on the nose of their saddles. They are doing it for aerodynamics, and for easier transition to running, but they are sitting on their junk.

KOPS and other more modern methods are there to get your pelvis in a good orientation to use the saddle as it was designed to be sat on. You use whatever seat post gives you good setback. Too much set back is rarely a problem, but too little (which zero setback posts often cause) is a problem.

The OP should have his bike built for a normal setback post, because that is the standard for road bikes. Everyone else should start with a setback post because that is more likely to provide correct fit - *especially for short riders who are already contending with artificially steep seat tube angles*. Zero set back posts on drop bar style bikes should only be used when they are essential for proper fit - which is relatively rare, in my experience.


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## appleSSeed (Nov 17, 2005)

Why so serious?


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## rx-79g (Sep 14, 2010)

appleSSeed said:


> Why so serious?


Erectile dysfunction is serious stuff.


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## appleSSeed (Nov 17, 2005)

rx-79g said:


> Erectile dysfunction is serious stuff.


So true! Lol


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## Elfstone (Jun 27, 2006)

Wow, I can't believe how many folks chimed in to this thread, thanks for all the replies. I've read each and every post and boy did I go into panic mode. So I email Rex Cycles and got a phone call today from Steve Rex and he put my fears to rest. 

The seat-tube is at 73.5 degree and most road bikes for my geometry are at 74 degree. Steve explained that with this angle for my geometry I can still go with a setback seat-post if I feel I need to. I do have a diagram or drawing of the bike build if you folks would like to take a look at it? I can post later when I get a chance to scan it.

Peace


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## jermso (May 13, 2009)

and this all relative to crank length?


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## rx-79g (Sep 14, 2010)

jermso said:


> and this all relative to crank length?


Not really. There are several different methods to setting saddle location when changing crank length, and one is leaving the saddle alone.

As cranks move in tiny 2.5mm increments, it really isn't an enormous problem, either way.


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## olr1 (Apr 2, 2005)

What this does call into question is the need for a custom frame.....

You're getting a bike built to fit you perfectly that has the option to _change_ the fit?

Ummm, ok....

The range of adjustability in modern off the peg bikes is suitable for most people; get custom because you want to, because you like it, but don't fool yourself that the fit will be better than a well set up off the peg bike.


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## mcwenzel (Jun 9, 2006)

FWIW, I was professionally fit on two bikes recently, a 2005 Orbea Onix and a new 2011Roubaix, two bikes with differing geometry. 

I need a zero setback seatpost on both to achieve the optimum position. Until I replace the posts, which I have not yet done, I am riding with the seat as far forward as it will go on the rails.

In addition, moving the seat forward from my prior position resulted in an increase in saddle height and saddle to bar drop. 

I am an avid recreational cyclist but was fit by someone who also fits pros.


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## stevesbike (Jun 3, 2002)

olr1 said:


> What this does call into question is the need for a custom frame.....
> 
> You're getting a bike built to fit you perfectly that has the option to _change_ the fit?
> 
> ...


+1 - custom frames are like custom license plates. There's a reason they're called vanity plates...


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## looigi (Nov 24, 2010)

I think it's been said a number of time by a number of posters already, but what matters is where the saddle is with respect to the cranks for your specific fit. What happens between the frame geometry and seatpost to get the saddle in the right spot doesn't matter, as long as it winds up in the right spot. Currently I have 3 road bikes, one with a traditional post with setback and two with zero setback seatposts. All three have are set up to same relative position between the saddle and cranks. 

If you're getting a custom bike fit to you and the designer its arranging things to use a zero setback post, it'll be fine, assuming he's not out to lunch.


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## SlowMover (Jun 6, 2010)

krisdrum said:


> Huh? Sorry, may be dense today, but I am trying to visualize this and just am not getting it. How does setback have anything to do with saddle height? The way I am envisioning it (and am totally open to correction), is we are basically rotating around the BB. Seat tube angle in conjunction with setback determines where we sit in relationship to the BB. But optimal saddle height is optimal saddle height as is determined by your physiology. As you rotate around the BB, the distance between BB and saddle top remain the same, they are just oriented at a different angle. Seat tube angle and saddle setback don't change your leg length, do they?
> 
> I agree that steeper seat tube angles "appear" to have a higher saddle position, but I am not convinced that a slacker seat tube angle would necessitate lowering your saddle height to get the same knee bend at the bottom of the pedal stroke.


IF one wants to preserve their optimal hip angle at BDC you MUST increase saddle height as you move the saddle forward. Here is a simple experiment for you to prove it. Mark your saddle at the top dead center above the rails and measure from the center of the bb. Now move the saddle all the way forward on whatever seat post you are using and do not change the seat post height. Now measure again from the center of the bb to that same top dead center spot and it's going to be less than what you measured from the initial position. It has to....simple geometry. Remember, you are dealing with a seat tube that is NOT vertical, it's at an angle....most likely 73-74 degrees.

My BDC hip angle on my road bike at 73*, middle of the rails on a Romin is 91 degrees>>>saddle height to center of rails is 794

My BDC hip angle on my P3 at 79*, middle of the rails on a Romin is 91.>>>>>>>saddle height to center of rails is 809.

All of those numbers are verified on a Retul with Zin of the coordinates.

Here is another misconception that fits in with this topic. If two identical bikes with two identical saddles have the nose of the saddle placed directly over the center of the bb, but one has a saddle height of 750 and the other of 800. Do they have the same effective STA given the center of the saddle as the prescribed rider position?

What do you think?


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## rx-79g (Sep 14, 2010)

SlowMover said:


> IF one wants to preserve their optimal hip angle at BDC you MUST increase saddle height as you move the saddle forward. Here is a simple experiment for you to prove it. Mark your saddle at the top dead center above the rails and measure from the center of the bb. Now move the saddle all the way forward on whatever seat post you are using and do not change the seat post height. Now measure again from the center of the bb to that same top dead center spot and it's going to be less than what you measured from the initial position. It has to....simple geometry. Remember, you are dealing with a seat tube that is NOT vertical, it's at an angle....most likely 73-74 degrees.
> 
> My BDC hip angle on my road bike at 73*, middle of the rails on a Romin is 91 degrees>>>saddle height to center of rails is 794
> 
> ...


That you just made something simple complicated.

The amount of saddle height variation you'll get by sliding the saddle fore and aft on the distance of its rails is going to be tiny. The rails only allow a few centimeters of travel. So if you start the process with the saddle on what you think is the right post and the rails centered, the saddle height can only change a millimeter or two. Which is well below the accuracy threshold of the rest of the saddle height calculation.


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## SlowMover (Jun 6, 2010)

Well I agree these topics can get complicated and it was more than was probably needed. 

I can tell you with mathematical certainty the variance on my Arione(my previous flat saddle) had 58mm of fore/aft travel from weld to weld on and FSA 32mm setback post clamp. That equaled 16mm of saddle height which is HUGE! That may not be much to you, but it's a ton for someone who is struggling to understand why they can't get comfortable after they jam the saddle full forward on the rails. I don't want to derail this guys thread any more than I have, sorry to the OP for getting off topic. My engineering gets the better of me sometimes and I go cuckoo.


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## rx-79g (Sep 14, 2010)

SlowMover said:


> Well I agree these topics can get complicated and it was more than was probably needed.
> 
> I can tell you with mathematical certainty the variance on my Arione(my previous flat saddle) had 58mm of fore/aft travel from weld to weld on and FSA 32mm setback post clamp. That equaled 16mm of saddle height which is HUGE! That may not be much to you, but it's a ton for someone who is struggling to understand why they can't get comfortable after they jam the saddle full forward on the rails. I don't want to derail this guys thread any more than I have, sorry to the OP for getting off topic. My engineering gets the better of me sometimes and I go cuckoo.


Is that including the fact that most saddle rails are sloped (from a level top), so the seat automatically slides up as you move it forward?


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## stevesbike (Jun 3, 2002)

a point not mentioned yet: saddles differ in their rail to front of saddle dimension, e.g., I can use a selle italia slr with zero setack but not a fsa or fizik saddle. They require a setback post for the same frame


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## SlowMover (Jun 6, 2010)

That is a very astute observation that shows you are on the right track, yes, it ^^could^^ lead to a higher saddle height, but not necessarily.

If you have a flat saddle AND the top of the saddle is parallel and level to the rails you will still get a progressively lower and lower saddle height as the saddle is pushed forward. Great point to bring up though b/c it's often a tough fitting aspect with coutoured saddles and rails that are not run concurrently level when dealing with fit spec changes. 

Short of doing the experiment yourself with your own gear the easiest way to see this very quickly is with a data point system like the Zin from Retul. 

But I digress and apologize to the OP for going away from the topic. The genesis of my post was to help 'krisdrum' understand the slippery slope of changing fore/aft positions and not adjusting saddle height. Moving it forward 5mm, meh, most probably wouldn't notice. I would change it simply b/c I'm a real stickler for mm's and not 'feeling' my way around. It comes from decades of TT trials and erros on a lot of different frames, learning the FIST protocol and the like. I ^^used^^ to feel my way around in generalities, but after taking the time to learn Dan Empfield's FIST fit protocol for tt fits I found out it's really pretty doggone simple to replicate each and every time with great accuracy Same thing goes for a road bike too. Replicating that hip angle is done a bit differently, but the same kind of detail oriented number crunching gets one very close the first time around . With that said numbers only give a range, but you do need a good starting point, IMHO.And I enjoy it too....but I will say that moving a saddle 4 and 5 cm in either direction w/o adjusting height will ^^more than likely^^ leave most cyclists scratching their head and struggling with comfort. 

Good luck with the new bike OP!


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## rx-79g (Sep 14, 2010)

SlowMover said:


> That is a very astute observation that shows you are on the right track, yes, it ^^could^^ lead to a higher saddle height, but not necessarily.
> 
> If you have a flat saddle AND the top of the saddle is parallel and level to the rails you will still get a progressively lower and lower saddle height as the saddle is pushed forward. Great point to bring up though b/c it's often a tough fitting aspect with coutoured saddles and rails that are not run concurrently level when dealing with fit spec changes.
> 
> ...


You know, I've used all different methods of fitting up my various road bikes. Sometimes I copy dimensions from another bike, other times I've done the fit from scratch. One time I compared all of them, and they were so close in important dimensions that I concluded that it really doesn't matter how you do it, as long as you do it carefully. A dental floss plumb-bob and a yard stick or tape measure are sufficient. 

BTW, I don't think it pays to get too anal with mm precision on things like seat height. Most saddle heights are the product of relatively imprecise measurements (like inseam or leg angle). I'm not suggesting being sloppy, but a mm here or there is an insignificant digit compared to the accuracy of the starting numbers.


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