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  #1  
Old 07-13-2021, 12:32 AM
Kingson Kingson is offline
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saddle height is confounding me

i have 2 bikes that have fairly similar geometry. Look has 74.5 sta, vs 73 for Focus
2016 Focus Izalco Max
2007 Look 585

both have 172.5mm cranks
same Fizik Arione saddles
same pedals
same shoes

they both have nearly identical saddle setbacks (from center of BB)
they are measured the exact same way. from center of BB, through the center point of the clamping area on the rails to level top of the saddle

but the saddle height on the Look is 5mm higher.
but both have the same feel when seated and riding

Last edited by Kingson; 07-13-2021 at 12:38 AM.
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  #2  
Old 07-13-2021, 12:52 AM
robt57 robt57 is offline
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hypotenuse...
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  #3  
Old 07-13-2021, 01:11 AM
Kingson Kingson is offline
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Quote:
Originally Posted by robt57 View Post
hypotenuse...
they both have the same saddle setback from the BB
so essentially the same sta
but even if one was further back, the length from the center of the bb to the top of the saddle remains the same, according to leg length
in any case, if one saddle was further back than the other, it wouldn't be a hypotenuse, its the radius of an arc.
or else the Lemond (and all other) measurement methods would have to take sta into account

i guess it really doesn't matter. they both fit. i just find it strange

Last edited by Kingson; 07-13-2021 at 01:24 AM.
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  #4  
Old 07-13-2021, 06:42 PM
Peter P. Peter P. is offline
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If your saddle to handlebar drop between bikes is different or your reach to the bars varies between each bike, it will affect your saddle height.

Your hips have a rotational pivot point which isn't exactly the center of the circle.
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  #5  
Old 07-13-2021, 06:42 PM
Peter P. Peter P. is offline
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Delete duplicate post.

Last edited by Peter P.; 07-14-2021 at 06:09 AM.
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  #6  
Old 07-13-2021, 08:57 PM
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David Kirk David Kirk is offline
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So....I'm not sure I get it.

Are you saying that you have two different bikes and one has a saddle height that is 5mm different than the other yet they feel the same to you?

dave
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  #7  
Old 07-14-2021, 07:24 AM
marciero marciero is offline
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Quote:
Originally Posted by Kingson View Post
...
they both have nearly identical saddle setbacks (from center of BB)
they are measured the exact same way. from center of BB, through the center point of the clamping area on the rails to level top of the saddle

but the saddle height on the Look is 5mm higher.
but both have the same feel when seated and riding
The way you are measuring it is independent of saddle fore/aft. The center of the clamping area is determined by the sta and seatpost alone. So it makes sense that you need the seatpost, and hence the saddle, higher on a bike with steeper STA to get the same measurement* here. It would be better to compare horizontal distance BB to nose of saddle. For quick and dirty, to have the same setback your saddle will need to be significantly farther back, rails relative to seatpost clamp, on the Look in order to have same setback. 1cm per degree is a rough estimate. All assuming same seatpost. Also, assuming no variation in rail profile. I am not sure about the latter. Even on the same saddle manufacturing tolerances may vary. But that would be noise compared to the big difference in sta.

Edit: *By which I mean setback measurement obtained this way

Last edited by marciero; 07-14-2021 at 12:54 PM.
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  #8  
Old 07-14-2021, 10:03 AM
chrisroph chrisroph is offline
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Measure to the same point on the saddle and report back. Going through the center of the clamping point of the rails--if I understand what you mean by that--makes no sense. If its 5mm different to the same point on the saddle, you must be very insensitive to saddle height.
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  #9  
Old 07-14-2021, 12:49 PM
marciero marciero is offline
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I'd also like clarification as to which of height and setback you were measuring through the clamp center-both, only height, or only setback. My previous remarks assumed setback - measuring horizontal dist from bb to clamp center, or to a point on the saddle through the clamp center from bb. Not so easy to measure this.


In any case, if the saddle setback were in fact the same on both bikes, with the saddle slid further back on the rails on the the 74.5 sta bike, and measuring height through the clamp center, then you would in fact be understating the height difference. My guess is that the setback is not the same on these bikes.

Quote:
Originally Posted by Peter P. View Post
If your saddle to handlebar drop between bikes is different or your reach to the bars varies between each bike, it will affect your saddle height.

Your hips have a rotational pivot point which isn't exactly the center of the circle.
Or at least the perceived saddle height. Maybe this also explains why saddle tilt affects perception of height. In my experience, tilting forward feels like lowering the saddle. If you removed the OP's saddle and seatpost from the 73 sta bike and installed it on the 74.5, the saddle would be tilted slightly forward, though at the exact same height.

Last edited by marciero; 07-14-2021 at 01:13 PM.
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  #10  
Old 07-14-2021, 01:34 PM
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bb center from the floor the same on both bikes?
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  #11  
Old 07-14-2021, 01:37 PM
Latestart Latestart is offline
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Stack/Reach

Are you saying that properly measured both bikes have the same Stack and Reach, but different ways to get there?
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  #12  
Old 07-15-2021, 09:32 AM
benb benb is offline
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If you don't have an expensive X/Y tool the way to do this is *always* to measure straight up the seat tube.

There is too much error in trying to do things like measure through the center of the clamp on different bikes with different seatposts.

The bike with the more *slack* seat tube needs the higher seat height when measuring straight up the seat tube.

The seat tube is the hypotenuse of a triangle.

The setback is the "opposite" side of the triangle.

The actual "Y height" of the saddle is the "adjacent" side of the triangle.

First take one bike, adjust that to where it is comfortable.

Now measure height straight through the seat tube. That is your hypotenuse.

Solve for the adjacent side to get the "Y" height.

Now take the other bike, start with the "Y" height, and solve for the hypotenuse, that is the height to set that bike to by measuring straight from the BB through the seat tube.

The setback is much simpler, once you've got the saddle height the same on the two bikes put the bike in an inside corner. Measure from the wall to the BB. Then measure from the wall to the saddle nose. Subtract the second from the first to get the setback. Then adjust as needed.

The difference here is pretty small. I have a bike with a 72.5 degree STA and another one with a 73.3. The difference is about 2-3mm in terms of the height they need to be at. It's on the verge of being something you can ignore, but if you want it to be exact doing the simple trigonometry can get two bikes feeling near identical.

Stack and reach is meaningless here if you're talking about the saddle. Stack and reach describe the position of the top of the head tube relative to the BB. If you've solved for your saddle position to get the saddle in identical places you can use the stack and reach after that to calculate whether you can get the bars the same on the two bikes and/or to figure out what length/angle/stem & # of spacers are required to duplicate the relationship between the bars & saddle.

I keep a spreadsheet setup to do this math.. I can just plug in the geometry of a frame and it does things like calculate where I need to put the saddle to get the same Y height and what to do with stem + spacers.

Last edited by benb; 07-15-2021 at 09:37 AM.
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  #13  
Old 09-07-2021, 08:46 PM
klasse klasse is offline
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I ride my saddle at the height that feels comfortable and works. I think it varies from bike to bike. I know it's higher up than what the "book" says it should be.

I have also shrunk about 1" - 2" in the past few years, so this works.
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  #14  
Old 09-09-2021, 02:14 AM
rustychisel rustychisel is offline
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Quote:
Originally Posted by Tickdoc View Post
bb center from the floor the same on both bikes?

Bingo!!! Also shoutout to Wakatel Luum.

Measuring from BB centre to saddle will tell you essentially nothing except that the bottom bracket is higher or lower.

Rotate cranks to parallel the seattube. Measure from saddle top (level) to centre of pedal spindle on lowest crank.

Repeat this exercise on the other bike.

Adjust accordingly. Consider how seattube angle may affect setback and reach.
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  #15  
Old 09-11-2021, 06:29 PM
ducati2 ducati2 is offline
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Or, just ride them and forget about it since they feel the same to you and it’s only 1/5th of an inch.
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