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seatpost setback vs. increased height pros and cons(10 posts)

seatpost setback vs. increased height pros and consMaartin
Mar 6, 2003 6:58 AM
I am looking to upgrade a Trek 5200 with a Icon 204 gram 27.2 x 250 mm seatpost to something better. I have a wonderful new Fizik Aliante seat. My main reason is that the Icon is open at the top where the plastic cap is and water has been getting in and ruining my bottom bracket. If not i do not see a reason the switch as most seatposts weight 180 grams anyway. Anyway ... how or why do people decide if and how much setback to go with. What is the advantage of setback ?
Mar 6, 2003 9:18 AM
You must be able to position your knee in the desired position relative to the bottom bracket. This is called the knee over pedal position (KOP). The starting point during a fitting drops a plumb bob from the front of the knee so it intersects the pedal spindle, with the crank arm horizontal. This is only a starting point that is refined by on the road experimentation. If the saddle is moved further back from this neutral position the ability to apply torque is improved, but cadence may suffer. The trick is to find the optimum combination of torque and cadence to produce the most power.

Power = torque x cadence. If you lose some ability to spin, the difference must be made up by increasing the torque applied to the pedals.

Ideally, the seatpost that you select should provide a reasonable amount of fore and aft adjustment from whatever position that you believe to be your optimum. If you run out of saddle travel, you've got the wrong post.
Great Information...Thank youMaartin
Mar 6, 2003 10:57 AM
A name you can trust.Sintesi
Mar 6, 2003 7:32 PM
C-40 rocks. : )
Yup, C-40 indeed rocks. nm.mainframe
Mar 7, 2003 9:17 AM
Mar 6, 2003 3:54 PM
If you run out of saddle travel you may also have the wrong frame. Making big changes to your knee to pedal position using large setback amounts or far forward positions is probably a sign also that your frame is not properly fitted to you. Big adjustments with seatpost and saddle also change your balance over the bike which can lead to a myriad of handling issues. Ideally, you should not have to make large saddle setback or seatpost setback adjustments to find your designed knee position relative to KOP starting point for a properly matching frame for your geometry.
one measurement worth a thousand wordsEric_H
Mar 6, 2003 4:40 PM
If you have the Aliante mounted to your Icon post and you are not at the limit of the rails in either direction, then a seatpost with roughly the same offset is what you need. This is assuming you are happy with your current fore-aft saddle position relative to the bottom bracket

What you need to know is the distance from the midline of your seapost to the leading edge of the seat rail clamp (horizontal distance). Now, this is not an exact measurement because you have to eyeball the centerline of the post, but you should be accurate within a couple of millimeters. Also, take note if your saddle is pushed all the way back on its rails.

Next, go to you your local shop with ruler in hand and measure a few high end posts to determine the amount of setback they have. Try to select something close to your current post, but if you have your saddle already all the way back, select something with a little more offset. The saddle rails will potentially have a better lifespan if you have the clamp centered in the middle of the rails instead of having them all the way back.
you hit the nail on the headaltidude
Mar 6, 2003 8:46 PM
Glad to see someone finally did.
my thumb hurts...C-40
Mar 7, 2003 7:38 AM
Nice answer, but to the wrong question. The answer basically says: "Buy a new seatpost with a clamp that is in the same position as the one you have." Well duuuh!

IF the requestor has the new saddle mounted on his old seatpost - IF it's in the correct position (for optimum KOP) - IF it has ample fore/aft travel remaining, then why would he ask a question with such an obvious answer?

The requestor asked why you would select a particular amount of setback and what the advantage of setback was.
then pull it out of your.....Eric_H
Mar 10, 2003 10:48 AM
To me, the question was basically about the poster wanting to buy a new seatpost. He realizes there are varying amounts of setback. He wonders how to choose. Well, sounds to me like I answered his question.

You answered his question, but then it became some kind of sermon on KOPS and power. Last time I checked, seatpost setback (note I do NOT say saddle setback) is not related to power output.