I always thought it was just a matter of moving your seat back and forth. Could you explain more please?

Changing your setback messes with your pedal stroke because it changes where your knees are in relation to the pedals. fa63 is correct, don't mess with setback to adjust reach. Reach should be adjusted with different length stems.

The point is that your saddle and your bars should be adjusted separately. The first step is to position your saddle where you want it and the second step is to position your bars where you want them. If you need to adjust your reach, only do it by changing the bars, changing the stem, or getting a new bike with a different top tube length. Never move your saddle to adjust your reach, as this will throw off your saddle positioning.

There's nothing wrong with a straight seatpost instead of a setback seatpost, but these are separate issues from reach.

So stem for reach and saddle for leg positioning. It is possible though that if someone were oddly proportioned they could replace the setback with a straight post just to get the knee positioned properly and then adjust the reach with the stem.

Or will that change the handling of the bike?

It's fine to play with setback seatposts vs. straight seatposts as long as you're doing it for the right reason, which is to adjust your saddle position.

Saddle/fore aft positioning is not only about placing the knee in a particular position relative to the pedal spindle. Although dropping a plumb bob from the knee to the pedal spindle, or the front of the crankarm is a common practice, a number of well-regarded fitters do not believe in it. They follow the idea of getting the rider's weight properly balanced over the saddle. Most often, that's further back than a KOP check would suggest.

https://www.cyclefitcentre.com/pdf%20final%20docs/backyard%20positioning_julu_aug_2004.pdf
https://www.cyclefitcentre.com/pdf%20final%20docs/THINGS%20YOU%20MAY%20NOT%20HAVE%20KNOWN%20ABOUT%20BIKE%20POSITION_final.pdf
https://www.peterwhitecycles.com/fitting.htm
https://www.sheldonbrown.com/kops.html

Saddle set back is critical in positioning your body mass fore and aft, and as noted above, most people have it set too far forward. If the saddle is too far forward, you will have to support your body with your arms, which is not good. You should have as little weight on your arms as possible. Too far forward and you will also be falling forward onto the nose of your saddle.

Adjust fore and aft by feel, not by using strings and plumb bobs. Move the saddle back until, when you are in your normal riding position on the tops of your bars (not hoods or drops), you can just lift your hands off the bars and ride no handed without falling forward.

"Adjust fore and aft by feel, not by using strings and plumb bobs. Move the saddle back until, when you are in your normal riding position on the tops of your bars (not hoods or drops), you can just lift your hands off the bars and ride no handed without falling forward."

Hi San Rensho; if I do that I'd still have to straighten my back and sit upright - is that what you mean?
I can only ride without leaning/touching the bars, sitting upright.

Let me amend that, you should be able to take your hands off the bars and ALMOST be able to ride no handed. You will tend to fall forward some, but it should be minimal.

https://www.peterwhitecycles.com/fitting.htm

I strongly recommend this article also. He does a really good job of explaining weight balance and and the reasons we choose to put a seat in different places. In essence you should be in a natural bent over position so when your feet are on the pedals and you are seated you shouldn't be falling forward but be balanced on the seat.

Yes.
That is exactly what I must do, (short torso with long legs).
Upon having knee issues, I started reading all I could on fitting, and found that I needed to ditch the setback seatposts and go to straight ones.
The knee issues are gone, *and* I am much more comfortable on the bike.

Considering that 2/3 of your weight on a road bike is on the rear wheel, and only 1/3 on the front, (I measured it), going to a less rear-biased weight distribution can only *improve* handling, especially when climbing steep grades.

I've heard set back seatposts were used mainly for bikes with more aggressive seat tube angles (STA).

Confusion reigns. Setback posts are the norm, for the vast majority of road bikes. With the general trend toward steeper STAs, setback posts are now more important than ever. Finding a nonsetback post on a pro's bike is rare.

The front to rear weight balance should not be 2/3 on the rear. I use a lot of saddle setback, with the nose of my saddle 6-7cm behind the BB center at a 73cm saddle height. Even with a lot of setback and a short torso, I have about 45% of my weight on the front wheel. Anything less than 40% is too light, IMO. The weight balance should be measured with the rider in his most agressive cornering/descending position.

Agree with this 100%. I've always told riders (when asked), that you should be able to ride on the tops with the bar in your fingers vs leaning on it in your palms. Look at the Pro's, riding PR on cobbles with a light touch on the bars. Nothing magic, just good fit.

All to often you see a newbie w/o enough set back, leading to too much weight on the hands, leading to them shortening the stem or raising the bars in a mis-guided attempt to compensate. You get the classic hunched up, stiff armed, un-aero, uncomfortable "Fred" position on a bike.

It took me almost a year to find out that I had to level my saddle - with the tip pointing upwards very slightly actually - to overcome crotch issues, pressure, etc. After reading your comments I may have another go at fore/aft issues ;-) Helpfull article Peter Whitecycles.

NO! You want essentially no weight on your arms when you are riding and if you move your saddle forward to alter for weight distribution, you will be putting weight on your arms which is the WORST thing that you can do for handling. The best handling comes from the lightest touch on the bars which you will not have if your your seat is forward and you are holding yourself up with your arms.

In addition, in any corner, the 1/3- 2/3 bias you measured goes out the window because the proper technique in a fast corner is to lift yourself slightly out of the saddle with your outside leg, so the weight distribution while you were in the saddle goes out the window.

Dave tell us again how many pros you have fitted since you bring them up so often?

I use a non-setback post. My STA on my current rig is 73.5. I have very small legs and smaller than normal femurs. With a setback post it feels like I'm "reaching" with my legs to make a full pedal stroke. Fitting is just like anything else.... there are a variety of opinions on the topic. Some say KOPS, some say not KOPS, and some say other things. I was fitted by someone considered to be one of the best in So Cal (and he actually has fitted pro cyclists) and he uses KOPS as a starting point. Just get fitted by someone with a good reputation and tweak if you're uncomfortable or experience displeasure. The notion to do what the pros do is so ridiculous that I'm still surprised people bring it up.

Thanks for your rudeness. Feel better now? Did I say I was in the business of fitting pro riders?

KOP is fine as a starting point, but nothing more. I'm not far off it - no more than 2cm back, but I also have a very short torso. Longer torsos are more common and a longer torso usually requires even more setback.

Find me a picture of a pro bike, particularly a euro pro, using a nonsetback post. Someone else tried a couple of months ago and failed. They found some straight posts, but the seat rail clamps were all set back. A true zero setback post has the center of the seatrail clamp over the centerline of the seat tube. It's far more common is see setback posts and the saddle slammed all the way back. If the frame brand happens to have a 72.5-73 degree STA, it's more likely that you might find an occasional nonsetback post, with the saddle all the way back.

I usually need a post with a fair amount of setback.. I know that I am a little too far back when my back starts to tell me.. One of the nicer setback posts is the VO Seapost.. 30mm of setback.. These are also ideal if you decide to use a Brooks saddle which has very short rails.. If I use a zero setback post, I end up placing the saddle all the way back to the end of the curve in the rails, usually 20mm of setback is enough for proper adjustment..

https://www.velo-orange.com/vogrcrusepol.html

32mm actually

not that the last 2mm should really matter if the frame is built correctly.

Wasn't rude but you always talk about pros this and pros that... however you don't seem to have ANY experience fitting a pro (let me know if I'm wrong but I do believe they tend to ride frames a size or two small ... maybe this explains why they all have set back posts....). I don't even necessarily disagree with you or your fit but you make blanket statements so easily with no apparent credentials that it's important people know there are many opinions on the topic. I agree not many (if any) pros ride with a zero setback post but not many (if any) ride with only 2-3 inches of drop like some of the board members (myself included). Maybe I should get a -30 stem to get more pro?

I do hope to make it to CO at some point so we can have this discussion the proper way over a pint and a burger

robncircus...

All you have to do is look at the pictures of euro pro bikes at any of several websites that cover pro racing to see how the bikes are setup. You don't need any credentials to do that. It's obvious they use lots of setback, lots of reach and lots of drop.

My only credentials are a mechanincal engineering degree (1981) and 26 seasons of riding. I've learned a thing or two in all those years. Even though I'm fast approaching 57 years old, I tolerate an 11cm drop and I credit that to being properly balanced over the saddle, with little weight on my hands. If I move my saddle forward even 1cm, I start to feel the pressure on my hands.

Just to clarify, having a short torso or long legs has no effect on whether you may need a setback post or not, assuming you're talking about the same frame and same rider position. It's only if you have short or long femurs in relation to tibia length that setback is affected.

So the most important factor is the STA of the bike (because every 1 degree steeper needs about 10mm more setback to compensate). After that comes the rider's preference for where they want to be in relation to the KOPS "easy-to-measure" reference point. If you like being 20mm behind KOPS, like DaveSSS. then a setback post may be necessary even on a relatively slack 73 degree STA frame. But 20mm behind KOPS is quite a lot. I doubt most people are that far back.

You've missed the whole point of this discussion, that KOP is not considered to be relevant by many well-regarded fitters who pay NO attention to femur length. It's mostly about weight balance. Longer torsos will require more setback to achieve a proper weight balance and femur length has nothing to do with it. My saddle setback preference has nothing to do with femur length. My point is that I use a lot of setback even with a short torso and a long torsoed rider would need even more to be properly balanced.

Using a further back position can also help recruit the use of the glutes, rather than being so dependent on the quads - very important if you do a lot of climbing like I do.

if you go for shorter crank arms, lets say 165mm over 170mm, you might find that you have to sit further back to keep the weight off your hands.