Seatpost angle and observations

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HUMP DIESEL
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by HUMP DIESEL

In an ever increasing theme to my post (bike fit), I have noticed that on a bike line such as Cervelo, the STA is 73 degrees, but more of the guys run set back seat post which would in turn put the angle even shallower. If I look at most people in a given group of riders around me, you see a good number of the direct opposite.

Any opinions on why?

HUMP
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dmp
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by dmp

I don't think you can equate this to seat tube angle. If all you look at is the position of the saddle relative to the bottom bracket, you might think of it in those terms, but that's not really accurate. Say the rider needs 2cm of setback to get properly positioned. If you slacken the seat tube angle to achieve that with a straight seat post, you would have to lengthen the chainstays to avoid hitting the seat tube with the rear wheel, thereby also completely changing the geometry and the handling characteristics of the bike.

Saddle setback is especially affected by leg (femur) length and torso length (and the relationship between the two). It's much more practical to adjust the saddle position with the seat post setback and sliding the saddle back and forth than to have bikes of so many seat tube angles.

HUMP DIESEL
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by HUMP DIESEL

I agree with that in part, what I was getting at is that it seems that on a bike with a shallower STA, and also a setback post that the riders on the Cervelo for instance seem to be sitting further back over the rear wheel, or they are sitting lower on the bike to keep KOPs within a given range.

HUMP
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KWalker
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by KWalker

A lot of pros have their seats way too far back and are constantly riding way up on the nose. I bet quite a few Garmin riders would do with a lot less setback, but this is how they're comfortable and I guess it works for them.
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stella-azzurra
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by stella-azzurra

The seat setback is really determined by your flexibility and the ability to ride in that position without compromising power.

https://www.stevehoggbikefitting.com/bi ... oad-bikes/
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thisisatest
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by thisisatest

my observations on the cervelos is that the seat tube does not necessarily bisect the bottom bracket. it passes in front of the bottom bracket, especially one the S-series, so their need for seatpost setback may be misleading.
that said. there are plenty of folks on cervelos with inline posts as well...

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Getter
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by Getter

How much difference does one degree make on a seat tube...say 74 to 73?

xcnick
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by xcnick

Getter wrote:How much difference does one degree make on a seat tube...say 74 to 73?


Depends on your saddle height. At my saddle height of 675mm the difference is about 10mm. I used this stem chart-just put the stem length as your saddle height

http://alex.phred.org/stemchart/Default.aspx

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fa63
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by fa63

A good rule of thumb is about 1 cm per degree.

Valbrona
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by Valbrona

stella-azzurra wrote:The seat setback is really determined by your flexibility and the ability to ride in that position without compromising power.


Spot-on.

And what also matters is what type of riding you do. If you live in Flatlandia by all means let KOPS be your starting point, but if you have hills and mountains and where it is commonplace for you to climb in the saddle KOPS will often place a saddle too far forward.

A road cyclist is not meant to have 'one' position on his/her saddle. Instead, the idea of a saddle is to provide a number of positions. The phrase 'on the rivet' actually explains quite a lot.

ultyguy
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by ultyguy

The Steve Hogg piece is right on for me, KOPS is a joke. I've moved from 7-8cm setback to 5 and I can definitely generate a lot more power, even climbing, and most of this is coming from the 'phasic' muscles. I also agree with the weight on hands part.

Edit- if you climb a lot, you should go forward, not back, as the increase in slope effectively gives you more setback anyways.

sawyer
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by sawyer

I've always ridden far forward.

If I put my seat back I lose power which may be down to flexibility.

Far forward is I believe an advantage on the flat if you correspondingly push the bars out to keep the back as flat as possible - i.e. effectively a TT position.

Conversely it is a disadvantage descending as there is too much weight on the bars - though as indicated this can be mitigated in part through sliding back (albeit the saddle is slightly too high).

Electronically adjustable saddle height will be an innovation in road biking at some point I believe. There are performance benefits to sitting lower down when descending.
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ultyguy
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by ultyguy

Yup, actually, Basso has already run a road 'dropper' post...
http://www.cyclingnews.com/features/pho ... ics/180519" onclick="window.open(this.href);return false;

And yes, I definitely have to put my butt back over the end to get the grip right on descending.

edit- Angelo Morelli patent info...
http://www.google.co.uk/patents/US8024992

sawyer
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by sawyer

pah - US patent indeed.

As everyone knows including the US Government as they have full oversight of my online activity, I came up the idea with it years ago - have posted on this forum before as it happens. :lol:

Seriously, an electronically adjustable seatpost per se as opposed to a specific design will not be patentable.

It's a very good idea with I'd suggest greater performance benefits than electronic shifting.

Shimano are the guys to do it ... (well, first)
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HUMP DIESEL
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by HUMP DIESEL

sawyer wrote:I've always ridden far forward.

If I put my seat back I lose power which may be down to flexibility.

Far forward is I believe an advantage on the flat if you correspondingly push the bars out to keep the back as flat as possible - i.e. effectively a TT position.

Conversely it is a disadvantage descending as there is too much weight on the bars - though as indicated this can be mitigated in part through sliding back (albeit the saddle is slightly too high).

Electronically adjustable saddle height will be an innovation in road biking at some point I believe. There are performance benefits to sitting lower down when descending.


When you moved the saddle back, did you also lower it to keep the distance from BB to center of saddle the same? Also would need to reduce the stem length to keep the reach the same.

I have been wanting to try this on my bike, but I have to buy another seatpost, because mine now will not allow me to get the seat far enough back. I need the FSA with the extra set back or something of similar set back or more.

HUMP
Why are the best things in life always the ones you start last?

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