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Seat posts vs bike fit

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Seat posts vs bike fit

Old 07-13-09, 07:05 AM
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d2create
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Seat posts vs bike fit

Calling all wise roadies...

So I'm looking around at seat posts and some are straight while others are set back.
Now I know that different amounts of setback can help you achieve the correct fit, but if your legs are supposed to be at a certain angle at a certain pedal extension, shouldn't we all be using the same style seatpost? Wouldn't you start there (with the correct size bike frame), and then adjust everything else to achieve the correct fit? Even the seat itself can be adjusted back and forth to some extent.

So what would be the optimum seat post style/setback to start with? Does the style of riding/riding position matter?

So confused.
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Old 07-13-09, 07:16 AM
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Originally Posted by d2create View Post
Does the style of riding/riding position matter?

So confused.
Dear SC,

Yes. All riders go for a different angle of attack from the seat to the pedals. Some perch on the saddle nose, others sit on the wide back. Some spin. Others mash. Some frames are upright, others are laid back.
You've got to find what works with your riding style, saddle, and frame geometry.

Hope this helps.
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Old 07-13-09, 07:57 AM
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Riders have different proportions, among other things, different length upper and lower legs.

Bikes have different geometries. Cranks have different lengths.

Hence no one size fits all answer.
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Old 07-13-09, 08:20 AM
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Almost all road bikes are designed to be used with setback seatposts. However, different people have different body proportions, so different people will need different saddle positions.

Straight seatposts are most popular with triathaletes and time trialers who want a more forward riding position on their aero bars.
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Old 07-13-09, 09:27 AM
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Rule of thumb:
front of knee is directly over the pedal axle when the crank is paralell with the ground, your style may vary.
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Old 07-13-09, 11:12 AM
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I had a setback seatpost with my saddle slammed forward to get the proper fit, so I got a straight post and now have the saddle more centered on the rails.
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Old 07-13-09, 11:56 AM
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Originally Posted by merckx_rider View Post
Rule of thumb:
front of knee is directly over the pedal axle when the crank is paralell with the ground, your style may vary.
ahhhh... ok, that helps me visualize where the differences come into play. Thanks!
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Old 07-13-09, 12:16 PM
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KOP is nothing but a starting point and too far forward for many riders. If the very front of the knee is used as the point to drop a plumb line from, then the front of the crankarm is often the preferred reference point. Other suggest dropping the line from the boney protrusion below the kneecap to the pedal spindle.

I prefer a position that is 10-20 further back to reduce the weight on my hands. The 51cm LOOK frames that I ride have a relatively steep 74.5 degree STA, so a 25 or 32mm setback post is a must. Witha 25mm setback, I've got some saddles pushed all the way back to get enough setback. The only time I used a nonsetback post was with an older LOOK that had a 72.5 degree STA that moves the saddle rail clamp back about 25mm further.
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Old 07-13-09, 12:52 PM
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Bike parts are made in different shapes and sizes because people do to.
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Old 07-13-09, 12:59 PM
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you honestly won't know what you'll need until you get your fit dialed in or want to copy your old setup to a new frame.
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