why use a Set Back Seatposts ?

[cnighbor1]

what is the idea behind a Thomson Masterpiece Setback Seatpost 27.2 x 240mm Or any setback Seatpost
doesn't the use of one indicate top tube on the frame is too short for that rider? or stem is too short?
I can't really figure out why the need of a set back Seatpost
thoughts
Charles

[Mzilliox]

Hey Charles, I used to wonder the same thing.
Here is my take, and im not sure how accurate it is, so take it with many grains of salt.

1. Setback seatposts i have heard are more comfy and absorb shock better...
2. From a geometry standpoint, you dont want too slack of a seat tube for a few reasons, but mainly to keep the wheels where they should be, and the rider's front center where it should be. but some riders still require being further behind the bottom bracket, so a bit of setback allows the rider to get in the correct position with regards to the bottom bracket. some riders do not require that, some riders do. I know that from riding different bikes i like a seat angle of 73-74 degrees. but to put me in the right place with regards to the bottom bracket, i need a touch of setback.
3. a set back seatpost should NOT be used to alleviate fit issues such as reach... as moving it for this purpose will put the rider in the wrong position for optimal pedalling.

[ripvanrando]

Seat angle is too steep for proper bike fit that gives the rider balance.

Few modern non-custom bikes that I have ridden would work for me without a setback post

[ripvanrando]

He explains it better.....but it is about balance and comfort for me

https://www.stevehoggbikefitting.com/bikefit/2011/05/seat-set-back-for-road-bikes/

[rwsaunders]

"My eyes refuse to watch them, maybe I'm too old?" Dario Pegoretti referring to non-setback seatposts.

[Luwabra]

upon my paid for "pro fit" we discovered that my femurs are way longer than the norm. so my reach is good but my knees were killing me bc I couldn't get the placement of the saddle where it needed to be. I suppose I could get longer crank arms but I can achieve the correct kops ish placement with a setback post. not that KOPS is a concrete placement but its pretty damn close to where he put me without using a plumb bob or anything. I don't know if this is right or not but its the way i achieve comfort as in no Knee pain. even with a setback post my saddle is usually slammed all the way aft.

??? .....following this thread.

[hampco]

Historically, many saddles sat further forward than modern saddles do - take a look at a Brooks Pro to see a good illustration of this. So a setback post would get the rider where he needed to be without an overly-slack seat tube angle, which introduces its own set of problems.

So it's partly an anachronism that we still use them - like nipples on males - and partly aesthetics, as they look correct on a road bike.

[nooneline]

what is the idea behind a Thomson Masterpiece Setback Seatpost 27.2 x 240mm Or any setback Seatpost
doesn't the use of one indicate top tube on the frame is too short for that rider? or stem is too short?
I can't really figure out why the need of a set back Seatpost
thoughts
Charles

the purpose behind a setback seatpost - which is a very ordinary bike part - is to get the relationship between the hip and the bottom bracket where it ought to be.

nobody says that you have to choose a bike with a seattube angle that lets you use a straight seatpost. you could just as easily be asking "doesn't the use of a no-setback seatpost indicate a top tube or stem that is too long?" but either way it would be the same moot point, since nobody should use seatposts (or saddle position, essentially) to handle reach issues - those can be adjusted with things that don't so directly affect your pedaling.

think of seatpost choice as doing to your pedaling what stem length does for reach - affords you a measure of adjustability. you size your bike, and you refine your position with other adjustable choices: seatpost, stem, handlebar, crank length.

[ergott]

Use whatever seatpost you need to center the rails (more or less) and achieve this.

http://kirkframeworks.com/2009/06/19/riding-tip-3/

For me that's a setback seatpost with typical bikes my size.

[David Kirk]

I think it's possible that many are reading too much into this.

Way back in the day high quality posts were designed with setback because it was simply easier to package the clamping hardware behind the post and not on the post centerline.

Once that was done most frames were designed to work with a traditional setback post....and in line with this saddle rail design was tied to a setback post.

The important part is that each rider has three contact points and those points relate to each other in a certain way. Within reason it doesn't matter how those dots are connected and if one is designing a frameset to fit a given rider either type post, setback or non-setback, can be made to work.

dave

[palincss]

what is the idea behind a Thomson Masterpiece Setback Seatpost 27.2 x 240mm Or any setback Seatpost
doesn't the use of one indicate top tube on the frame is too short for that rider? or stem is too short?
I can't really figure out why the need of a set back Seatpost
thoughts
Charles

You would need a setback post in order to get the saddle to the proper position vis a vis the bottom bracket. Different saddles have rails of varying lengths, and frames have varying seat angles. With a short-railed saddle like a Brooks or Berthoud, I need both a setback post like a Nitto S83 and a seat angle of between 71 and 72 degrees to get my saddle to the proper position for me; with a 73 degree seat angle I need a seat post with a lot of setback like a Nitto S84.

Since these factors describe every bike I've ever owned, what I can't understand is the use for a zero offset post.

[KidWok]

The important part is that each rider has three contact points and those points relate to each other in a certain way. Within reason it doesn't matter how those dots are connected and if one is designing a frameset to fit a given rider either type post, setback or non-setback, can be made to work.

dave

Agree with this. Found this recently on Open Cycles' website about their U.P.:

Zero-setback seattube
With a minimalist 27.2mm diameter we maximize the flex in our seatpost & seattube. This is especially a big plus on rough terrain. The seattube angle is designed around the use of a straight, zero-setback seatpost rather than a regular seatpost with setback (we’ve never understood those). Zero-setback posts are lighter, saving you another 10-30 grams (every little bit helps and you can then put that saved weight into a 500g saddle like the Brooks!).

I find it weird that a production bike company went so far as to take a stand on this. Why say anything about this when fit is specific to rider's measurements?

FWIW...most of my bikes are around a 73-73.5 STA and I'm using setback posts that have ~1.5cm offset. I have a Lemond MJ Spline that uses a straight post with the saddle pushed all the way back to get the same position because it has a 72.5 STA.

To the OP's point though, the Thomson setback post is ugly. It sticks out like a sore thumb on any bike I've ever had it on.

Tai

[saab2000]

Historically, many saddles sat further forward than modern saddles do - take a look at a Brooks Pro to see a good illustration of this. So a setback post would get the rider where he needed to be without an overly-slack seat tube angle, which introduces its own set of problems.

So it's partly an anachronism that we still use them - like nipples on males - and partly aesthetics, as they look correct on a road bike.

This is pretty much true. Modern saddles have longer useful rail sections. I use 20+ year old Selle Italia Turbomatic saddles on several of my bikes and they pretty much require a setback post and to have the saddle slammed all the way back.

On a few other bikes I use Fizik Arione saddles and they're pretty much centered, though still with some setback on the seatpost itself.

And yes, aesthetically a setback seatpost looks appropriate in most applications. Vanity is a great thing.

[Climb01742]

Since many of us buy frames used, getting our saddles where they need to be requires different post setbacks. Setback is just a tool to get our butts where they belong. And whether a zero setback post looks good or not tends to depend on the totality of the bike, not simply the post.

[drewellison]

Because Eddy used one.

[Kontact]

To get the same position using the same section of rails on a saddle, a bike using a zero setback seatpost would have to seat tube angle that is 2.5° shallower than standard.

So instead of a 73° STA, you'd need a 71.5° STA. Has anyone seen many of those, lately?


Open Cycles uses 72.5° STA, across the board, so they think everyone should have the equivalent of a 74° STA. Which is ridiculous.

[avalonracing]

I'm a normally proportioned 6'0 guy and prefer a zero setback post and a 74ºSTA. Must be from spending too many years riding the rivet.

[Kontact]

I'm a normally proportioned 6'0 guy and prefer a zero setback post and a 74ºSTA. Must be from spending too many years riding the rivet.

You have an atypical riding position that is closer to something on a tri bike.

[macaroon]

The key thing is really pelvis angle and torso angle and whereabouts they are on the bike.

Short torso/long legs? Probably want an inline seatpost

Long torso? You'll likely want a setback seatpost.

There's a current trend in pro cycling for small frames/long stems/very low bars. This sort of setup usually requires an inline seatpost, but it really all depends on individual body proportions.

I think a common myth is that long legs mean a setback seatpost to get KOPS. So if you've got very long legs, you'll end up with a massive amount of saddle setback and all your weight will be way off the back of the bike.

An inline post might also be beneficial if you spend all your cycling time riding up big hills. Going up hill slackens your seat angle even more meaning your weight goes even further backward.

I'm not in the mood to type more at the momet.

Fuzzalow covered it well some years ago.

[Kontact]

The key thing is really pelvis angle and torso angle and whereabouts they are on the bike.

Short torso/long legs? Probably want an inline seatpost

Long torso? You'll likely want a setback seatpost.

There's a current trend in pro cycling for small frames/long stems/very low bars. This sort of setup usually requires an inline seatpost, but it really all depends on individual body proportions.

I think a common myth is that long legs mean a setback seatpost to get KOPS. So if you've got very long legs, you'll end up with a massive amount of saddle setback and all your weight will be way off the back of the bike.

An inline post might also be beneficial if you spend all your cycling time riding up big hills. Going up hill slackens your seat angle even more meaning your weight goes even further backward.

I'm not in the mood to type more at the momet.

Fuzzalow covered it well some years ago.
I totally, totally disagree with this.

You set your saddle position based on your legs, nothing else.

You set your reach AFTER you have found saddle position.


Long and short legs have the same proportions and require a similar degree of set back.



The hill climbing part would be sensible only if climbing hills never involved going back down them.

[macaroon]

I totally, totally disagree with this.

You set your saddle position based on your legs, nothing else.

You set your reach AFTER you have found saddle position.


Long and short legs have the same proportions and require a similar degree of set back.

What do you mean "based on your legs"? As I said, KOPS is a myth, it's been discredited by various respected people. Once you read what they're on about, it all makes sense.

Niki Terpstra using a setback seatpost the wrong way round! Check his position though, works perfectly for him. If he was going for a ride to the shops he might want some high handlebars and a bit more saddle setback for comfort; correct tool for the job etc.

http://cdn.velonews.com/wp-content/uploads/2014/03/SPTDW1041-1.jpg

[macaroon]

The hill climbing part would be sensible only if climbing hills never involved going back down them.

Well duh, it's all about compromise isn't it! No bike will handle and ride the same uphill as it does downhill.

[Kontact]

What do you mean "based on your legs"? As I said, KOPS is a myth, it's been discredited by various respected people. Once you read what they're on about, it all makes sense.

Niki Terpstra using a setback seatpost the wrong way round! Check his position though, works perfectly for him. If he was going for a ride to the shops he might want some high handlebars and a bit more saddle setback for comfort; correct tool for the job etc.


KOPS isn't a "myth", unless you believe that KOPS is describing some sort of actual phenomenon. In reality, KOPS is a tool that happens to produce fairly reliable results for setting leg angle. That's all it is for.


If we could see the hip joint easily we would simply locate the hip at a certain number of degrees from a line running through the BB. We can't, so we use KOPS to approximate it.


Whether you have a 28" inseam or a 34" inseam, you still want the same proportional seat height, and you want your leg to extend in front of you by the same angle. If you don't you start changing not just leg angle but pelvic angle and weight distribution. A person with long legs has no good reason to sit right above the cranks than a short person does, so they both use the same average leg angle.


Don't be fooled by a couple of guys riding in outlandish positions. That isn't how road bikes are designed to work, and it isn't how saddles are designed to interface with the pelvis. The guy in the picture, pro or not, looks ridiculous and is riding on his taint.

The reason pros are using smaller frames is because all the high end bikes have tall head tubes to suit the 50+ riders who have incomes to buy $10,000 bikes. So the pros can only get their stems down by dropping a frame size and using a long stem. That has nothing to do with set back.


I state all of this as someone who worked closely with a top fitter for several years and produces an ergonomic bike saddle. You are way off.

[Kontact]

Well duh, it's all about compromise isn't it! No bike will handle and ride the same uphill as it does downhill.

Which is why you would have the same set back whether riding on flats or hills. Because you don't want to descend with all your weight on the front wheel.

Duh.

[sales guy]

I need a setback post for my long legs. 6'3 and a 36" inseam. Need it on a mountain bike too.

Setback posts help for fitting. It really is that simple.

[avalonracing]

You have an atypical riding position that is closer to something on a tri bike.

Maybe... Kinda like the guy in post #21

[Kontact]

Maybe... Kinda like the guy in post #21

Your poor groin.

[macaroon]

Whether you have a 28" inseam or a 34" inseam, you still want the same proportional seat height, and you want your leg to extend in front of you by the same angle. If you don't you start changing not just leg angle but pelvic angle and weight distribution. A person with long legs has no good reason to sit right above the cranks than a short person does, so they both use the same average leg angle.


I don't really understand what you mean by
leg extending infront of you by the same angle?
use the same average leg angle?



Don't be fooled by a couple of guys riding in outlandish positions. That isn't how road bikes are designed to work, and it isn't how saddles are designed to interface with the pelvis. The guy in the picture, pro or not, looks ridiculous and is riding on his taint.


It's more than "a couple of guys" though. Everyone seems to be doing it nowadays; super slammed stems and the saddle forward. I agree though, the bikes will probably not handle best in this position. As for how the saddle interfaces with the pelvis, everyone is different. Some people roll their pelvis further forward than others, Chris Froome sits pretty much bolt upright.

[macaroon]

Which is why you would have the same set back whether riding on flats or hills. Because you don't want to descend with all your weight on the front wheel.

Duh.

You kinda missed my point. Ideally you wouldn't have the same setback, ideally you'd be able to adjust it (along with the position of all the other parts) for riding uphill. And then adjust it at the top for the descents. But if you're spending the majority of your time going UP hill, you might prefer to set your bike up to make it most comfortable/efficient for that purpose.

[macaroon]

I need a setback post for my long legs. 6'3 and a 36" inseam. Need it on a mountain bike too.

Setback posts help for fitting. It really is that simple.

Setback posts on an MTB is strange aswell. The industry seem to be making seat angles steeper and steeper as it aids seated technical climbing.

[sales guy]

Setback posts on an MTB is strange aswell. The industry seem to be making seat angles steeper and steeper as it aids seated technical climbing.

Long legs. I've tried a straight post and it puts me over the front too much. Hurts my knees a bit too.

[macaroon]

Long legs. I've tried a straight post and it puts me over the front too much. Hurts my knees a bit too.

More "reach"? Check this one out, 77 degree seat angle! http://www.geometronbikes.co.uk/G16.html

[sales guy]

More "reach"? Check this one out, 77 degree seat angle! http://www.geometronbikes.co.uk/G16.html

Hell No! I can't stand slack geometry. Hate the way they ride and the way I feel on them. I have a new 29'er being made for NAHBS in a custom geo. Can't wait for it to be finished. It'll be a rocket.

[Kontact]

I don't really understand what you mean by
leg extending infront of you by the same angle?
use the same average leg angle?


The BB is in front of the seat, because the seat tube is angled back. So from the saddle your leg is angled forward toward the crank. The number of degrees it is angled forward is pretty much the same for short and tall people, so it makes no sense to change the effective seat tube angle with different set back posts for different leg lengths.

[marciero]

Hey Charles, I used to wonder the same thing.
Here is my take, and im not sure how accurate it is, so take it with many grains of salt.

...

2. From a geometry standpoint, you dont want too slack of a seat tube for a few reasons, but mainly to keep the wheels where they should be, and the rider's front center where it should be...



This. It seems that lots of bikes, esp. race bikes, have rather tight rear triangles with little clearance between seat tube and rear wheel. For riders that do require setback, putting the saddle where it needs to be with slack STA rather than setback seatpost would require lengthening chainstays, thereby changing weight distribution, handling, etc. Even on bikes with more wheel clearance, slackening the STA would make for tighter wheel clearance disproportionate with other clearances. I suppose you could use the Hot Tubes curved seat tube approach...

[Kontact]

You kinda missed my point. Ideally you wouldn't have the same setback, ideally you'd be able to adjust it (along with the position of all the other parts) for riding uphill. And then adjust it at the top for the descents. But if you're spending the majority of your time going UP hill, you might prefer to set your bike up to make it most comfortable/efficient for that purpose.

And you missed mine. It is very difficult to spend all your time climbing since you eventually get to the top and have to go down the other side.

[ultraman6970]

77 degrees in a mtb/dh or whatever bike??? cant imagine that and I dont do mountain biking. Dude maybe wants to be different?

Hell No! I can't stand slack geometry. Hate the way they ride and the way I feel on them. I have a new 29'er being made for NAHBS in a custom geo. Can't wait for it to be finished. It'll be a rocket.

[Kontact]

This. It seems that lots of bikes, esp. race bikes, have rather tight rear triangles with little clearance between seat tube and rear wheel. For riders that do require setback, putting the saddle where it needs to be with slack STA rather than setback seatpost would require lengthening chainstays, thereby changing weight distribution, handling, etc. Even on bikes with more wheel clearance, slackening the STA would make for tighter wheel clearance disproportionate with other clearances. I suppose you could use the Hot Tubes curved seat tube approach...

Or put a dent in it, or split it, or mold it out of carbon in any old shape you like.

That said, you would have to angle the post back quite a few degrees before you used up the standard tire clearance of a 410mm chainstay.

[sales guy]

77 degrees in a mtb/dh or whatever bike??? cant imagine that and I dont do mountain biking. Dude maybe wants to be different?

the headtube is 62.5. That's slack. Most are 68.5 or 66.5 now.

[marciero]

Or put a dent in it, or split it, or mold it out of carbon in any old shape you like.

That said, you would have to angle the post back quite a few degrees before you used up the standard tire clearance of a 410mm chainstay.

Indeed. The bikes I ride these days certainly have a degree or two to spare.

[pasadena]

The rules changed recently, so many more pros are pushing saddles forward and tilting the nose down now that it is legal.


Niki Terpstra using a setback seatpost the wrong way round! Check his position though, works perfectly for him. If he was going for a ride to the shops he might want some high handlebars and a bit more saddle setback for comfort; correct tool for the job etc.

http://cdn.velonews.com/wp-content/uploads/2014/03/SPTDW1041-1.jpg

[PacNW2Ford]

Or put a dent in it, or split it, or mold it out of carbon in any old shape you like.

That said, you would have to angle the post back quite a few degrees before you used up the standard tire clearance of a 410mm chainstay.

Not true: with a 70mm BB drop and a 73.5°, you're already running out of room to get an inflated 25mm tire out with horizontal dropouts.

[Kontact]

Not true: with a 70mm BB drop and a 73.5°, you're already running out of room to get an inflated 25mm tire out with horizontal dropouts.

You just described my 51cm Lemond. I see well over 1/2" of clearance.

But there is a reason vertical dropouts came into vogue. I'm not sure who makes good use of vertical dropouts - it usually seems like people have them in them adjusted full forward.

[ergott]

Use whatever seatpost you need to center the rails (more or less) and achieve this.

http://kirkframeworks.com/2009/06/19/riding-tip-3/

For me that's a setback seatpost with typical bikes my size.

Yes I quoted myself. Don't compare yourself to pros, it doesn't work. Do the above and you will happy on your bike.

[alancw3]

setback seat posts are only another dimension of fitting a bike to the rider. imho if a bike is fitted properly a zero setback should be used. but most people buy a used bike and have to fit by seat post setback and stem length.

i have used both over the past 50 years and i can tell you that there is nothing like a zero set back post for a solid feel while riding. if i were having a bike custom build i would specify a zero set back seat post as part of the design.

[ldamelio]

I had the same question as the OP a couple of years ago. Here's a thread from ATH that I started. Includes responses from some of the deans of American frame building.

https://www.velocipedesalon.com/forum/f2/educate-me-seat-post-setback-27950.html?highlight=educate+setback


Mods please feel free to delete if not OK to cross post.

[SoCalSteve]

I had the same question as the OP a couple of years ago. Here's a thread from ATH that I started. Includes responses from some of the deans of American frame building.

https://www.velocipedesalon.com/forum/f2/educate-me-seat-post-setback-27950.html?highlight=educate+setback


Mods please feel free to delete if not OK to cross post.

I’m not a mod ( nor play one on tv ) but if there is great information to be had, why not share that information? I’m sure the mods feel the same way. And, I also believe that there isn’t any animosity between the two forums.

[roguedog]

that was an interesting trip down the rabbit hole. :)

I had the same question as the OP a couple of years ago. Here's a thread from ATH that I started. Includes responses from some of the deans of American frame building.

https://www.velocipedesalon.com/forum/f2/educate-me-seat-post-setback-27950.html?highlight=educate+setback


Mods please feel free to delete if not OK to cross post.

[booglebug]

Just a question. If you’re not fighting sliding forward or sliding back on your saddle does it mean you’re close in your setback? Thinking that pedaling style could come into play, flat vs toes down.

[ldamelio]

I’m not a mod ( nor play one on tv ) but if there is great information to be had, why not share that information? I’m sure the mods feel the same way. And, I also believe that there isn’t any animosity between the two forums.


I understand, I'm active 85% over there, 15% here and enjoy both, just wanted to be respectful in case there were any considerations I was unaware of.

[Mark McM]

I totally, totally disagree with this.

You set your saddle position based on your legs, nothing else.[/QUOTE]

That clearly can't be the case at all. Your legs are not the only part of your body involved in pedalling. Here's why:

Every reaction has an equal and opposite reaction; so when you are pushing on the pedals with your legs, what is the reaction force in the opposite direction? On a recumbent, where your legs are horizontal, and the seat has a vertical seatback, you clearly push against the seatback. But on an upright bike, the reaction force the legs push against is gravity; specifically, the weight of the cyclist's body. The location of the rider's center of gravity plays a large role in determining how the rider can apply leg force during different parts of the pedal stroke.

Setback is used to place the rider's body weight over the cranks in the position for most effective pedalling. That is the basis of the previously mentioned rule of thumb about long torso/short legs using a bigger setback than short torso/long legs. A long torso projects the body weight forward from the saddle (and cranks), so the saddle should be moved back accordingly to compensate. Torso angle also plays a role in this.

You set your reach AFTER you have found saddle position.

While that has often been the simplified approach to fitting (based on strict adherence to KOPS), the reality is that setback can't be set until the upper body position is also set. Ti Designs has often discussed the relationship between saddle setback and rider CG - where is he when you need him?


Long and short legs have the same proportions and require a similar degree of set back.

This is also not true. The ratio of upper and lower leg segments also varies between people, and this also affect setback.

[Kontact]

setback seat posts are only another dimension of fitting a bike to the rider. imho if a bike is fitted properly a zero setback should be used. but most people buy a used bike and have to fit by seat post setback and stem length.

i have used both over the past 50 years and i can tell you that there is nothing like a zero set back post for a solid feel while riding. if i were having a bike custom build i would specify a zero set back seat post as part of the design.

Considering that nearly every manufacturer specs setback seat posts on road bikes, why would a properly fitted bike have the saddle moved forward an inch from spec?

I get that some people don't like set back seat posts conceptually, but you can't throw out an inch/2.5° of fit dimension without compensating for it.

[macaroon]

Considering that nearly every manufacturer specs setback seat posts on road bikes, why would a properly fitted bike have the saddle moved forward an inch from spec?

I get that some people don't like set back seat posts conceptually, but you can't throw out an inch/2.5° of fit dimension without compensating for it.

Manufacturers spec their bikes for the averages. The average person in an average position will probably require a setback seatpost.

The picture I posted on a previous page shows a position that isn't typical/isn't average, and a flipped seatpost has has been used to achieve it.

[Mark McM]

Which is why you would have the same set back whether riding on flats or hills. Because you don't want to descend with all your weight on the front wheel.

Duh.

Well you don't necessarily want the same set back for climbing and descending - you're just stuck with it.

Mountain bikes often riding on more varied terrain than road bikes - steeper climbs and steeper descents. That's why many MTB saddles are designed to allow the rider to slide both forward and backward on the saddle - forward is better for climbing, backward is better for descending. There have even been special seatposts made which allow the rider to slide the saddle forward and back as necessary. (This, by the way, is why mountain bike fitting is often considered not as critical as road bike fitting - on a mountain bike, the terrain is so varied, that there is not a single ideal rider position.)

But, even on a road bike, a single saddle setback may not be perfect. My current road bike setback works very well for most of the riding I do (which includes road and criterium racing). But I find that when road slopes up to steeply (greater than 10%), the change in the effective seat tube angle, plus sitting up more to allow better use of my glutes, my center of gravity falls too far back to allow me apply my body weight well to the pedals. When the road is really steep, I find that I have to slide forward on the saddle to be able to push down on the pedals more effectively. When I do hillclimb races on steep mountains (such as Mt Washington or Mt Ascutney, both of which have average grades of 12%), I modify my bike by pushing the saddle forward by about an inch for a better climbing position.

[Mark McM]

But there is a reason vertical dropouts came into vogue. I'm not sure who makes good use of vertical dropouts - it usually seems like people have them in them adjusted full forward.

There are lots of reasons vertical dropouts became popular - allowing shorter chainstays is just a minor one. The main reasons include:

- Allows tighter control of the position of the wheel/cassette with respect to the derailleur (this became more important with the advent of indexed shifting).

- Prevents pulling the wheel out of the dropout under chain force. (This is more important for MTBs, whose small chainrings generate far higher chain forces than road bikes, and which is why MTBs adopted vertical dropouts first.)

- Better manufacturing tolerances no longer required that axle position be adjustable for proper wheel alignment.

Chainstay lengths haven't changed much before and after vertical dropouts were adopted. If vertical dropouts allow easy wheel swaps on short chainstay bikes (without the necessity of deflating the tire), it is just a fringe benefit.

[macaroon]

But, even on a road bike, a single saddle setback may not be perfect. My current road bike setback works very well for most of the riding I do (which includes road and criterium racing). But I find that when road slopes up to steeply (greater than 10%), the change in the effective seat tube angle, plus sitting up more to allow better use of my glutes, my center of gravity falls too far back to allow me apply my body weight well to the pedals. When the road is really steep, I find that I have to slide forward on the saddle to be able to push down on the pedals more effectively. When I do hillclimb races on steep mountains (such as Mt Washington or Mt Ascutney, both of which have average grades of 12%), I modify my bike by pushing the saddle forward by about an inch for a better climbing position.

Dropping the nose of your saddle might even help somewhat.....or fitting a 26" front wheel :D

Alberto Contador is someone who often looks awkward climbing in the saddle; slid forward, right on the rivet, not relaxed at all. I've always thought he had his bars too long/low...... which I myself have found makes climbing out of the saddle more comfortable, and that's something he does alot of.

[Kontact]

Well you don't necessarily want the same set back for climbing and descending - you're just stuck with it.

Mountain bikes often riding on more varied terrain than road bikes - steeper climbs and steeper descents. That's why many MTB saddles are designed to allow the rider to slide both forward and backward on the saddle - forward is better for climbing, backward is better for descending. There have even been special seatposts made which allow the rider to slide the saddle forward and back as necessary. (This, by the way, is why mountain bike fitting is often considered not as critical as road bike fitting - on a mountain bike, the terrain is so varied, that there is not a single ideal rider position.)

But, even on a road bike, a single saddle setback may not be perfect. My current road bike setback works very well for most of the riding I do (which includes road and criterium racing). But I find that when road slopes up to steeply (greater than 10%), the change in the effective seat tube angle, plus sitting up more to allow better use of my glutes, my center of gravity falls too far back to allow me apply my body weight well to the pedals. When the road is really steep, I find that I have to slide forward on the saddle to be able to push down on the pedals more effectively. When I do hillclimb races on steep mountains (such as Mt Washington or Mt Ascutney, both of which have average grades of 12%), I modify my bike by pushing the saddle forward by about an inch for a better climbing position.

Yup, and maybe someday we'll have variable geometry bikes with angles and lengths and rakes that suit the speeds and conditions.

[macaroon]

Yup, and maybe someday we'll have variable geometry bikes with angles and lengths and rakes that suit the speeds and conditions.

:D Been done; see Canyon Shapeshifter........not sure how successful it's been though.

[Mark McM]

The BB is in front of the seat, because the seat tube is angled back. So from the saddle your leg is angled forward toward the crank. The number of degrees it is angled forward is pretty much the same for short and tall people, so it makes no sense to change the effective seat tube angle with different set back posts for different leg lengths.

Using the same seat tube angle for both short and tall rides would work, except for one thing:

You might think that as the legs get longer, both the height of the saddle above the BB and the setback of the saddle from the BB would change by the same proportion, and thus the angle from BB to saddle would be preserved. But we don't set the saddle setback by it's position relative to the BB, we set the saddle setback by its position relative to the pedals.

Now, if crank length also changed in proportion to leg length, then yes, seat angle could be kept constant between tall and short riders. But that would mean if a 60" tall rider with 30" legs used 165mm cranks, than a 72" tall rider with 36" legs would use 198mm cranks. Do you know any 72" tall riders using 198mm cranks? I didn't think so.

A 72" tall rider is more apt to use 175mm cranks, or 180mm cranks at the outside. Therefore, to compensate for these proportionately shorter cranks, the taller rider will need to push their saddle back (by 18mm - 23mm in this case) to maintain their same setback in relation to their pedals. To be able to use the same seatpost setbacks, the taller rider will need a shallower seat tube angle.

[Kontact]

Using the same seat tube angle for both short and tall rides would work, except for one thing:

You might think that as the legs get longer, both the height of the saddle above the BB and the setback of the saddle from the BB would change by the same proportion, and thus the angle from BB to saddle would be preserved. But we don't set the saddle setback by it's position relative to the BB, we set the saddle setback by its position relative to the pedals.

Now, if crank length also changed in proportion to leg length, then yes, seat angle could be kept constant between tall and short riders. But that would mean if a 60" tall rider with 30" legs used 165mm cranks, than a 72" tall rider with 36" legs would use 198mm cranks. Do you know any 72" tall riders using 198mm cranks? I didn't think so.

A 72" tall rider is more apt to use 175mm cranks, or 180mm cranks at the outside. Therefore, to compensate for these proportionately shorter cranks, the taller rider will need to push their saddle back (by 18mm - 23mm in this case) to maintain their same setback in relation to their pedals. To be able to use the same seatpost setbacks, the taller rider will need a shallower seat tube angle.

I don't follow. "The cranks" have a center point, and that centerpoint doesn't change with crank length.

[Mark McM]

I don't follow. "The cranks" have a center point, and that centerpoint doesn't change with crank length.

By center point, I assume you mean their central pivot - the bottom bracket. Yes, that is true. But we don't apply power to the center point of the cranks, we apply power to the end of the cranks (at the pedals). Furthermore, we get the most effective power when we push down on the pedals when the cranks are close to horizontal, in front of the center point. Therefore, we need to position our feet, legs and saddle to where the pedal is when we apply power.

This means that as the cranks get longer, we need to move forward, and as the cranks get shorter, we need to move backward.

If we could apply power to the pedal equally all around the circle, then we'd want to position the setback relative to the center of the circle. But since we get the majority of the power when pushing down on the pedal when it is forward of the center, we need to set the setback relative to this pedal position.

[wallymann]

to compensate for an overly steep seat-tube, allowing saddle to achieve desired setback.

[Kontact]

By center point, I assume you mean their central pivot - the bottom bracket. Yes, that is true. But we don't apply power to the center point of the cranks, we apply power to the end of the cranks (at the pedals). Furthermore, we get the most effective power when we push down on the pedals when the cranks are close to horizontal, in front of the center point. Therefore, we need to position our feet, legs and saddle to where the pedal is when we apply power.

This means that as the cranks get longer, we need to move forward, and as the cranks get shorter, we need to move backward.

If we could apply power to the pedal equally all around the circle, then we'd want to position the setback relative to the center of the circle. But since we get the majority of the power when pushing down on the pedal when it is forward of the center, we need to set the setback relative to this pedal position.
We don't sit on the seat to just produce power. It supports our weight, balances us to take weight off of our hands and helps us control the bike.

To maintain a generally useful position on the saddle you have to reference everywhere the legs are going to be, regardless of whether it is under power or not.


However, some of this stuff is self regulating because of foot size, the use of KOPS, etc. Super long cranks are generally only 1cm longer than "short" cranks. 1cm is well below the 2.5cm difference between set back and zero seat posts.

[ripvanrando]

Swapping longer cranks requires lowering the saddle and also moving it back a little bit (not forward) or at least in my experience going back and forth from "short" 177.5mm cranks to the 200mm big ones. Moving it back to keep the same balance......there is some trig in there.

[azrider]

The rules changed recently, so many more pros are pushing saddles forward and tilting the nose down now that it is legal.

:eek:

[BdaGhisallo]

:eek:


The best of both worlds!

[Ruimteaapje]

For me it is quite simple: for my ideal position on the bike the saddle is clamped 20 cm behind the perpendicular line from the centre of the bottom bracket. To achieve that with a non-setback seat post whilst keeping enough clearance between the seat tube and the rear tire, the wheelbase would be way too long

In the past I used a non-setback post on my Merlin but I had to clamp the saddle way too far to the front of the rails making it prone to snapping...

https://scontent-sea1-1.cdninstagram.com/vp/e9eb7a68c55af03f72de888387f7b180/5BE6EDEB/t51.2885-15/e35/30076281_170303470297671_7677925740125356032_n.jpg ?efg=eyJ1cmxnZW4iOiJ1cmxnZW5fZnJvbV9pZyJ9&ig_cache_key=MTc1NjY3NDIwOTg3MjA1NzU1MQ%3D%3D.2

[colker]

Hey Charles, I used to wonder the same thing.
Here is my take, and im not sure how accurate it is, so take it with many grains of salt.

1. Setback seatposts i have heard are more comfy and absorb shock better...
2. From a geometry standpoint, you dont want too slack of a seat tube for a few reasons, but mainly to keep the wheels where they should be, and the rider's front center where it should be. but some riders still require being further behind the bottom bracket, so a bit of setback allows the rider to get in the correct position with regards to the bottom bracket. some riders do not require that, some riders do. I know that from riding different bikes i like a seat angle of 73-74 degrees. but to put me in the right place with regards to the bottom bracket, i need a touch of setback.
3. a set back seatpost should NOT be used to alleviate fit issues such as reach... as moving it for this purpose will put the rider in the wrong position for optimal pedalling.

why 5 pages of posts after this reply?

[cadence90]

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[mcteague]

I never had a straight seatpost until now. After getting a Selle SMP saddle I found it had to be moved up much closer to the bars than previous ones. On top of that, the angle of the saddle is super critical to making SMPs work. So, I ended up with a straight Thomson post. The saddle is now in the middle of the rails and it is super easy to dial in just the right amount of tilt.

Tim