09 May, 2017

Seatpost Setback - A Scrutiny of Styles

By Scott

With Velo Orange expanding our range of products over the last few years, one of the newer items that we've developed is a Zero Setback Seatpost. Now, if you're a long time roadie, you may wonder why someone would want zero setback? So let's look into the mysterious world of bike fit and design to see why someone would want a zero/medium/long setback post.

Road bikes for years have had posts with setback- a seatpost where the clamping area for the saddle was behind the centre of the post that came up from the seatpost. The theory behind this was to allow for proper weight distribution (ideally 60 % on the rear of the bike, 40 % on the front). Assuming a 73 deg seat tube angle, the setback allowed one to fully engage the hamstrings and glute muscles more efficiently.

For most setback posts, the standard set back was around 25 mm or so. Why? Good question. My best guess is that it created the "medium" amount of setback that most people needed. With the costs of tooling to create different heads to the seatposts (this is all done with forging and dies), most folks went for the middle of the road to deal with the average.

Touring, city, and recreational riders tend to need more setback then a racer does. The more upright position requires more setback to put your legs in a more efficient bio-mechanical place.

The other factor is the rail length of the saddle. This is the ultimate limiting factor when it comes to proper position of the saddle, which ultimately effects where your knee and foot end up. Different saddle makers have different rail lengths. Traditionally Brooks and other leather saddle makers have had very short rails, thus the need for more setback in order to get the knee positioned correctly. In these cases, our Long Setback Seatpost is a winner. Our Model 3 Saddle  and Model 6 Saddle offer longer rails, so that you can choose which post style you'd like to dial in your riding position.

So why, after reading all this (thank you), does one need a zero setback post? Surely the above reasons make sense. Well, the rise of MTB's is one of the main reasons. The slacker and longer geometry of MTB's means that having zero offset puts the rider in the middle of the bike, rather then well behind the centre of the bike. Having more weight forward helped prevent you from toppling back on steep climbs and allowed you to move your butt behind the seat post on the steep descent. So MTB's tend to come with zero set back posts as standard. Zero set back posts also work if you have a short femur. The zero offset helps to put those folks over the pedal easier. Zero offset posts also work well if the top tube (real or virtual) is longer then ideal. Moving the seat forward reduces the distance between the stem and the saddle.

If you've got a theory about the relationship between setback, position, fit, and performance, let us know in the comments.


David Spiva said...

I always assumed "medium" setback came from the old timey literal seat posts that have the guts clamped on the top and saddle clamped to the guts.
All other accommodations for geometry were based off of that legacy until more recently when seatpost sizing became more consistent and frame manufacturers started including a seatpost with their bike as an engineered package.

Anonymous said...

Spiva's comment about seatpost setbacks being a legacy of the old style straight seatpost hardware design is probably spot on. Old fashioned frames were designed around the geometry dictated by the common and inexpensive seatpost mechanical design. I would also add that if one looks at photos of very old track style bikes they tended to have more relaxed frame angles, and the riders tended to place their saddles a bit further forward. Many times the straight seatpost clamp hardware was placed in FRONT of the post to allow the rider to get the saddle into the right spot. Wheelbases got shorter over time to sharpen handling, and seat tube angles got more steep to allow for shorter chainstays without clearance issues between seat tube and rear tire. The setback style forged seatpost made it easier for the rider to get to the same position relative to the pedals in a steeper-angled frame. Average angles, average setback, average length saddle rails all combine to give an average range of rider positions. It has been an evolution over time based on where most riders prefer to sit. All other things being equal, a slacker seat tube angle and a short setback post will get you into the exact same place.

John Duval said...

This leaves unanswered the question of why have setback in the first place, rather than simply change the angle of the seat tube to put the clamp in the correct spot. Once upon a time it was more of a practical matter of the design of the seat clamp. The clamp had an offset, so seat tubes were angled forward to compensate. But this feature still persists. But, having the option to change offset is good, now that we more often fit the bike to our bodies rather than contort our bodies to the machine as it comes.

Guessing which saddle and seat combination you need for a given fit can be a guessing game. Maybe some sort of chart.

TWC said...

"Touring, city, and recreational riders tend to need more setback then a racer does. The more upright position requires more setback to put your legs in a more efficient bio-mechanical place."

I don't agree with this. For me, the amount of setback has more to do with keeping weight off my hands. On a racing bike, I typically like more setback. Getting my butt back allows me to lean further forward via back support, and not requiring me to put too much weight on my hands. On a city bike, on which I will have a more upright riding position, weight on my hands is not an issue and the amount of setback I like has more to do with having a not-too-long distance to the bars.

Race bikes with aero bars (e.g., tri bikes) are an exception to the above. I am fine with supporting weight on my elbows. In this case, fore-aft saddle position relative to the spindle has more to do with whether I prefer low cadence pushing (aft) or high cadence spinning (fore).

Neil E. Hodges said...

You can only get so slack of a seat angle before you start compromising tire clearance for a given chainstay length. I think part of why 73° seat angles are all over is because you won't get 410mm chainstays and 25-28mm tires without doing weird stuff that'd raise the cost of the frame.

I have very long femurs for a guy (I know guys 5 inches taller than me with the same leg length as me), and I can only raise the saddle so much before my knees start hurting. Every one of my bikes needs a setback seatpost, even the one with a 71.5° seat tube angle (VO long setback post, saddle just a little too far back for a typical 20-25mm post), and the one with a 73° seat angle (out of the manufacturer's spec for my size) needs Nitto's 45mm setback post to work at all for me. I know part of it is the Brooks and Berthoud saddles I use, but I'd rather deal with odd seatposts than either knee pain or butt pain.

The only place where this isn't working out for me is with the BodyFloat seapost I recently got. I have a Brooks Team Pro on there now, and the combination of those on a 72° seat tube isn't working too well for me. I'm sticking with it until I test it enough to find strong enough evidence to justify a leather saddle with more intrinsic setback (VO and others provide plenty of options).

It's been a real journey for me over the past three years, figuring all this out. I've seen several bike fitters, and only the most recent one commented on my long femurs.

GAJett said...

I am pleasantly surprised to find that I'm not a total weirdo with my old-style style clamp in FRONT of the seatpost. I am rediscovering my 44 year old Raleigh Competition which is admittedly just too large for me. But by placing the clamp in front of the seatpost I can get up over the pedals and spin the way I like. This is one sweet-handling bike and I find I ride it more and more, liking it as much or more that my Rivy Hilson. It's amazing how different, but the same, they are, and both have a place in my life.

Jantzen said...

A little late. I too have very long legs for my height, esp my femurs. I have tried with setback posts on the road but all I end up doing is riding further ahead on the saddle. I'm sure that even if I stuck on a super short stem I'd still move more over the spindle.

When I am climbing on the road bike sure, I'll take lots of setback. But in the drops you are rotated forward and down. My road bikes all have about a 10cm saddle to bartops drop which is probably around average these days? (point is it's nothing extreme)

I'm completely lost on setback posts and it must just be me. In the 80's, for example, when saddles and bar tops were about level and bikes were 73/73 it makes sense to me because the rider is more upright. For me, that part of the article makes sense.

I just cannot see how when in the drops having your ass out and your pedals forward can possibly generate as much power as being more over the spindle, not to mention how uncomfortable it is.