Seat Forward/Aft Position - Explain it to me

It is typically measured as the distance of the nose of the saddle in front of or behind the bottom bracket center line.  The negative number indicates the saddle nose is behind the bottom bracket while a positive number indicates it's forward of the bottom bracket.
It's usually expressed in centimeters.

To measure it, you place a yard stick or carpenter's level across the top of the seat and you drop a plumb line from above that down toward the bottom bracket.  When the plumb line is vertical from the center of the bottom bracket you measure the distance from the saddle nose to the plumb line.

The advantage of being more forward is that you will generally have a limiter physically speaking to how tight your hip angle can be.  Let's say that you find it hard to breath and produce power at 95 degrees of hip angle.
If you reach 95 degrees of hip angle with your torso way the heck up in the air, you will be fighting wind resistance.  So drop your handlebars lower right?  well darn, now your hip angle is 90 degrees and you can't breath.
But if your seat is more forward it works to open that hip angle back up again.

So moving the seat forward allows your torso to be more level which makes you faster due to decreased wind resistance.

...also want to check the relation of the knee to the pedal spindle...

Put on your cycling clothing and shoes...and if you have a trainer, do a small warmup (5min) so you are comfortably positioned in your saddle. If not just have someone hold your bike upright and try to get in your "normal" position on the saddle.

rotate your foot to the 9 0'clock position of the crank, foot close to parallel to the ground, and drop a plumb bob (or string with weight tied on) from just beneath your patella (front of knee) straight down to the top of your shoe. Notice the relationship between where the center of the pedal lies to the plumb bob.

This will give you an idea of how far forward/aft you are of your pedal centerline. Along with the above example from the previous poster, this will give you a more informed idea of what muscle groups you are recruiting and what strains you could be putting on your knee.

Generally speaking, tri-athletes prefer to have their knee forward of the pedal spindle by 1-3cm....this recruits your larger upper legs for more power during sustained efforts. Most cyclist-only prefer to be centered on the spindle...recruiting both sets of fast and slow twitch muscles more easily (for sprints, etc). As a side note, some people that experience knee pains realize their saddle is too far back (knee is behind their pedal spindle)...this puts more strain against those weaker muscles.

It does boil down to personal preference, but its at least good to know how you are positioned. If you do decide to make changes, do so in small (<1cm) increments and ride for a week before moving any further.

Edited by Redline1 2011-02-14 11:33 AM

The concept of where the femur joins the pelvis relative to the bottom bracket, usually measured in horizontal proximity and often in "effective seat tube angle" is a fascinating one.

I once was part of a human powered aircraft experiment in an attempt to fly across several bodies of water such as the English Channel using a pedal powered airplane. As part of the engineering process they expereimented with different effective seat tube angles and their effect on power, heart rate, fatigue and even thermal response.

An additional study oft cited in triathlon media, the "Garside Study" by Ian Garside and Dominic Doran from June of 2000 has probably become the watershed argument for steep seat angles (close proximity of hips to bottom bracket measured horizontally). Some subsequent studies debunk Garside, but enough anecdotal evidence suggests that riders run better off a steep angle and the empiracle reality that a more open femur to torso angle is more comfortable maintains the relevance of Garside, et al.

So.

A steep seat angle may be "faster" for both T2 and on the bike in the aero posture. There are catches to this, and there is no one "fastest", but the trend toward steeper effective seat angles in Kona and elsewhere is pretty compelling.

One previous poster mentioned a dated fit metric known as K.O.P.S. or "Knee Over Pedal Spindle" as a landmark for fore/aft positioning of a saddle relative to a bottom bracket. Most fitters have eschewed and debunked K.O.P.S. entirely by now. With the development of better fit protocols and testing methodologies (power meters, Computrainer Spin Scan, etc.) K.O.P.S. is no longer a tangible "rule of thumb". It was better than nothing in the late '70's and early '80's. It doesn't apply to the athlete using an aero cockpit and running off the bike.

For a detailed understanding of this read some of Dan Empfield's excellent articles on triathlon bike fit and steep seat tube angles on his website at Slowtwitch.com.

I concur, although its a fine baseline to know if youre in the vicinity of 3cm +/- KOP, and alot cheaper (free) than computrainer, spin scan, etc.

As mentioned, It will definitely not perfect your fit at all.

Edited by Redline1 2011-02-14 12:14 PM

Interesting; anything to support any of this?

Shane

I don't like to be contrary, but I think he actually had it backwards.  Seat too far forward can sometimes create knee pain and moving the seat back can help.
But I am not really sure there is a direct correlation between the seat's position relative to the bottom bracket and which muscles are recruited.  I see that as more of a function of the hip angle and perhaps the ankle too.  If I take my road bike and slide the seat forward with no other changes, my hip angle opens up more and that would change recruitment...but if I then extend my stem and lower my bars to close the hip angle, the muscle recruitment changes back.

Think of a recumbant bike.  Do your muscles have eyes and look outside of your body to know where you are relative to the bottom bracket?  Nope, they just push against the pedals around a different portion of the arc.

If anything it goes like this:
Tighter hip angle, heel down = glutes
looser hip angle, toes down = lower quads

Tom, it seems you are primarily referring to tri bike fit, any insight on for/aft position on a road bike?

You are correct- I was predominantly discussing triathlon bike fit.

Road bike fit? Hmmm. Well, it is as much steeped in "lore" as it is in science. Even, or perhaps esepcially- today.

When Jacques Anquetil used custom long crank arms and no handlebar tape to win the Gran Prix de Nations (the unofficial "World Championship" of time trials in the late 1950's and early 1960's) a staggering 9 times from 1953 to 1966 everyone thought this was the way to go. He pedalled with an odd "toes down" technique that everyone emulated at the time. It must be right- Anquetil did it. He also smoked cigars and was a social gadfly, frequently seen with starlets and aristocrats.

Along came Merckx. A "scientist", a workman. He trounced Anquetil with a brutish style using buried heels, a low saddle and inelegant form. It was the new "right".

Then Hinault, LeMond, Indurain... Armstrong. And with Armstrong came Charmichael and the Internet age- where we are now.

One thing that has emerged is consumer level telemetry to measure relevant metrics that was unavailable to every Tour de France winner mentioned except Armstrong- partially because, for better or worse, he ruled nearly an entire decade during which technology development was accelerated.

So, ultimately, what is the best position on the road bike? Well, I'll suggest it resides at the point where highest power output with lowest physiological output converge with best aerodynamics. Those are three hefty metrics to try to converge. It isn't as simple as "Knee over Pedal Spindle", but guides like the ones proposed by the New England Cycling Academy (NECA) who invented the R.A.D. (rotational adjustment device) and original FIT KIT are certainly better than nothing at all.

After all this I hold a few truths to preside over bike fitting. They include:

1. It takes at least a year, usually two years, for the body to acclimate to sitting on a bike. That's right- it wasn't just "the wrong saddle". Before that time has elapsed an athlete is going to struggle with intermitent discomfort. It isn't the "wrong" saddle or bike fit usually. It is simply that the athlete is not yet adapted and conditioned to sit on the bike in an athletic, competitive setting.

2. Most American endurance athletes- including myself as I type this- are overweight. 3 pounds, 5 pounds, 10 pounds, 15 pounds, 20 pounds or more.  Losing weight and reducing body fat are the keys to performance, comfort and endurance. Power meters? Bike fits? Aerodyanmics? Nope. We all need to lose some weight before those factors will result in a tangible improvement.

3. As the bike adapts, so too must the athlete. They have to do work off the bike to facilitate and foster comfort and performance on the bike. Few of us do that dilligently.

I hope those insights and opinions help.

Tom: Can you say more about that? 

Thanks Tom.

You mentioned that the old knee over the pedal spinal is out dates and not necessarily the best route to go. I recently purchased a John Cobb saddle (max) and after reading the paper work that comes with the saddle noticed John has created a chart to help determine the for/aft seat position. How credible is this theory?

I know John Cobb has a lot of street cred these days (lol) but will his seat chart be in line with a better fit philosophy to help dial in the for/aft position?

John is one of the great "thinkers" of the industry and sport and a fine man.

In general, John's insights on fit are very well thought out and tested. I like his saddle designs also. I can certainly recommend John Cobb's insights into fit and saddle position. His ideas are based on solid fitting experience, research and insights.

Tom,

Thanks for several excellent posts on this thread.  I have learned a great deal and I am following up on your suggested reading.

Edited by 08M3Sedanski 2011-02-25 5:57 AM

When I ordered my Cobb saddle mid-season last year, I was nervous about having to dork around yet again with my bike fit, but I really wanted to try that Max saddle...  When it arrived, I decided to try out John's easy-peasy setup/fit instructions, and although I was skeptical of how simple the up/down-tilt-fore/aft instructions seemed to be, the "fit" ended up being super comfortable.  Just to make sure I wasn't just high on the Cobb kool-aid, I did swing by my shop to have them take a quick peek at the fit, and they agreed it looked spot-on.  

Many long rides since (including IMWI), and no complaints.  Cobb = good stuff!

Cheers, Chris 

I resent this statement.  As I stare at my gut it is indisputably true, but I still resent it.

Thanks for the insights, Tom.  Great discussion.