Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 35
  1. #1
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)

    Raise saddle after moving it forward?

    I keep looking for the answer to this question, but all I can find is the reverse: the need to move a saddle forward to maintain knee position after raising it. That is not what I am asking. I want to know how much do I have to raise my saddle after moving it forward (for whatever reason). I'm thinking the reach to the crank will have been shortened as the saddle moves more directly over it, not much but some. Anyone have a formula for this? I moved my saddle forward 1 cm.

    I did a really quick and dirty approximation that suggests the amount the saddle has to be raised x is about y(cos theta) where y is how much I move the saddle forward and theta is the seat tube angle. Assuming 73 deg I get roughly 0.3 of the distance moved forward (or backward and lowering the saddle). So for my 1 cm change, I would need to raise the saddle about 3 mm. Not only is that a very small amount, but my seat post is stuck, so I will likely ignore it for now. At least until I decide if I like the new knee position. I know the saddle height will affect this, but I will work it out as I go.

    Nevertheless, I would be interested in hearing what other folks come up with.

    Thanks.

    Robert

  2. #2
    Redefining Lazy Slackerprince's Avatar
    Join Date
    Apr 2008
    Location
    Tampa via PDX, Summers on LV-426
    My Bikes
    2013 Cannondale Synapse 5 105, 2013 Giant Escape 3
    Posts
    1,534
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    I do saddle adjustment by feel.
    I do use the rail #'s as a reference, but mostly it's a lot of times in and out of the garage with a hex wrench.


    S
    I'm not fat, I'm belly-breathing

  3. #3
    Portland, OR, USA pdxtex's Avatar
    Join Date
    Feb 2004
    Location
    portland
    My Bikes
    kona paddywagon, trek 2.1, lemond nevada city, gt zrx
    Posts
    1,620
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    id start with a baseline height using one of the popular formulas. i use the lemond formula (inseam x .883) to determine initial seat height (distance from top of seat to middle of bottom bracket). get that set first then do the fore/aft set up. feel pressure in front of your knees? move the seat back. feel like you are sitting on the narrow end of a 2 x 4? move the seat forward. make sure seat is level always. tah dah....
    we've got both kinds, country and western.

  4. #4
    Pentapointed Member ahsposo's Avatar
    Join Date
    Jan 2010
    Location
    On Some Far Away Beach After the Season is Over...
    My Bikes
    A Home Built All Rounder, Bianchi 928, Specialized Langster, Dahon Folder
    Posts
    6,361
    Mentioned
    10 Post(s)
    Tagged
    1 Thread(s)
    I thought the OP was the authority on bike related matters.
    Quote Originally Posted by toddles View Post
    If I gotta look up words, it's not worth my time.

  5. #5
    Senior Member gc3's Avatar
    Join Date
    Mar 2004
    Location
    DC
    My Bikes
    Now I Got Two
    Posts
    2,557
    Mentioned
    11 Post(s)
    Tagged
    1 Thread(s)
    Are we supposed to be applying math to this question? If so, then of course I am of zero assistance.

    However, I will rehash my Retul fit experience, wherein my saddle was moved one inch higher and almost an inch forward, resulting in optimized measured power output (still quite low by 41 standards). Therefore, according to my scientific sample size of one...ipso facto the ratio is 1/1....
    "I tried being reasonable, I didnt like it."

    "I understand. I just don't care"

  6. #6
    Senior Member gc3's Avatar
    Join Date
    Mar 2004
    Location
    DC
    My Bikes
    Now I Got Two
    Posts
    2,557
    Mentioned
    11 Post(s)
    Tagged
    1 Thread(s)
    Quote Originally Posted by ahsposo View Post
    I thought the OP was the authority on bike related matters.
    He used to be, but IMHO has measurably mellowed like fine wine...
    Last edited by gc3; 01-10-14 at 06:17 PM.
    "I tried being reasonable, I didnt like it."

    "I understand. I just don't care"

  7. #7
    Senior Member megalowmatt's Avatar
    Join Date
    Jun 2009
    Location
    North County San Diego
    Posts
    1,510
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Make the adjustment then post it in the "Hot r Not" thread. They'll tell you exactly the adjustment you'll need to make.

  8. #8
    Packfodding 3 caloso's Avatar
    Join Date
    Jul 2002
    Location
    Sacramento, California, USA
    My Bikes
    Ridley Excalibur, Gazelle Champion Mondial, On-One Pompino, Specialized Rock Hopper
    Posts
    29,474
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Rather than get out my TI-30, I just use a tape measure and measure from the center of the BB spindle to the center of the saddle rail. As I move the saddle forward, I have to raise it up so that it's the same distance.
    Cyclists of the world, unite! You have nothing to lube but your chains!

  9. #9
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by ahsposo View Post
    I thought the OP was the authority on bike related matters.
    Testy, eh?

  10. #10
    Pentapointed Member ahsposo's Avatar
    Join Date
    Jan 2010
    Location
    On Some Far Away Beach After the Season is Over...
    My Bikes
    A Home Built All Rounder, Bianchi 928, Specialized Langster, Dahon Folder
    Posts
    6,361
    Mentioned
    10 Post(s)
    Tagged
    1 Thread(s)
    Not really. Just was surprised is all.
    Quote Originally Posted by toddles View Post
    If I gotta look up words, it's not worth my time.

  11. #11
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by caloso View Post
    Rather than get out my TI-30, I just use a tape measure and measure from the center of the BB spindle to the center of the saddle rail. As I move the saddle forward, I have to raise it up so that it's the same distance.
    Sure, the empirical method should have been obvious to me. I was just wondering whether there was an established formula for this that soneone could supply

  12. #12
    Pentapointed Member ahsposo's Avatar
    Join Date
    Jan 2010
    Location
    On Some Far Away Beach After the Season is Over...
    My Bikes
    A Home Built All Rounder, Bianchi 928, Specialized Langster, Dahon Folder
    Posts
    6,361
    Mentioned
    10 Post(s)
    Tagged
    1 Thread(s)
    "established formula" = x+y-r/2
    Quote Originally Posted by toddles View Post
    If I gotta look up words, it's not worth my time.

  13. #13
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by ahsposo View Post
    "established formula" = x+y-r/2
    That's what I'm talkin' about. I can't wait to check this against the measurements. I'm guessing you will be anxious to know the results.

  14. #14
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by ahsposo View Post
    I thought the OP was the authority on bike related matters.
    Actually I admit to entering discussions with inferior knowledge, expressing what I think is correct and then using the rebuttals as a learning tool. Kind of a screwed up Socratic method.

  15. #15
    Senior Member RollCNY's Avatar
    Join Date
    Jun 2011
    Location
    Central NY
    My Bikes
    Felt Rejected
    Posts
    5,905
    Mentioned
    61 Post(s)
    Tagged
    0 Thread(s)
    STA is less relevant, as seatposts have offset. I would look at it as c=√(a+b). C is a constant, your leg extension, which does not need to be solved, as it will be the same before and after the change. If a is vertical and b is horizontal from BB, you now have √(a+b)=√((a+∆v)+(b-∆h)). Square both sides, use foil, and solve for ∆v.

  16. #16
    Pentapointed Member ahsposo's Avatar
    Join Date
    Jan 2010
    Location
    On Some Far Away Beach After the Season is Over...
    My Bikes
    A Home Built All Rounder, Bianchi 928, Specialized Langster, Dahon Folder
    Posts
    6,361
    Mentioned
    10 Post(s)
    Tagged
    1 Thread(s)
    Quote Originally Posted by rpenmanparker View Post
    Actually I admit to entering discussions with inferior knowledge, expressing what I think is correct and then using the rebuttals as a learning tool. Kind of a screwed up Socratic method.
    This makes you a 'made member' of the 41.

    Congratulations.

    Now lets do the ceremonial cleaning of the chain.
    Quote Originally Posted by toddles View Post
    If I gotta look up words, it's not worth my time.

  17. #17
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by RollCNY View Post
    STA is less relevant, as seatposts have offset. I would look at it as c=√(a+b). C is a constant, your leg extension, which does not need to be solved, as it will be the same before and after the change. If a is vertical and b is horizontal from BB, you now have √(a+b)=√((a+∆v)+(b-∆h)). Square both sides, use foil, and solve for ∆v.
    That looks completely correct. Is it not true that the trig approach I used inherently incorporates the formula you provided? You're right about the lack of need for using the STA, but I wonder if the use of it, just as an approximation doesn't simplify the whole process.

  18. #18
    Senior Member RollCNY's Avatar
    Join Date
    Jun 2011
    Location
    Central NY
    My Bikes
    Felt Rejected
    Posts
    5,905
    Mentioned
    61 Post(s)
    Tagged
    0 Thread(s)
    If you are going to use angles, I recommend switching to radians. If I get a choice, I love talking about pi rotating around my crank.

  19. #19
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by RollCNY View Post
    If you are going to use angles, I recommend switching to radians. If I get a choice, I love talking about pi rotating around my crank.
    Perhaps pi likes it too.

  20. #20
    Packfodding 3 caloso's Avatar
    Join Date
    Jul 2002
    Location
    Sacramento, California, USA
    My Bikes
    Ridley Excalibur, Gazelle Champion Mondial, On-One Pompino, Specialized Rock Hopper
    Posts
    29,474
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by rpenmanparker View Post
    Sure, the empirical method should have been obvious to me. I was just wondering whether there was an established formula for this that soneone could supply
    I nominate this statement to be the new motto of the Forty-One.
    Cyclists of the world, unite! You have nothing to lube but your chains!

  21. #21
    Senior Member RollCNY's Avatar
    Join Date
    Jun 2011
    Location
    Central NY
    My Bikes
    Felt Rejected
    Posts
    5,905
    Mentioned
    61 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by caloso View Post
    I nominate this statement to be the new motto of the Forty-One.
    I'll second the motion provided you support my campaign to have "Iron Alloy Appreciation Week". I am still working on a pithy slogan like "Steal a moment for Iron Alloy" or "The irony of Iron Alloy" or "Iron Alloy: it is your father's alloy" or "Available for Centuries for centuries".

  22. #22
    Senior Member RollCNY's Avatar
    Join Date
    Jun 2011
    Location
    Central NY
    My Bikes
    Felt Rejected
    Posts
    5,905
    Mentioned
    61 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by rpenmanparker View Post
    That looks completely correct. Is it not true that the trig approach I used inherently incorporates the formula you provided? You're right about the lack of need for using the STA, but I wonder if the use of it, just as an approximation doesn't simplify the whole process.
    Yes you could solve with angles. I wouldn't because you don't care what the starting or ending angle are, but you will need to solve them, and use them in a subsequent equation. They are intermediate calculations to move from ∆v to ∆h. If you can make a formula that uses only ∆v &∆h, why not solve direct?

  23. #23
    Galveston County Texas 10 Wheels's Avatar
    Join Date
    Nov 2007
    Location
    In The Wind
    Posts
    25,092
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Wear two three pairs of shorts.
    [SIZE=1][B]What I like about Texas[/B]
    http://www.youtube.com/watch?v=PGukLuXzH1E

    Set F1re To The Ra1n ( NY Night Rain Ride)
    http://www.youtube.com/watch?v=W7jfcWEkSrI

  24. #24
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by RollCNY View Post
    I'll second the motion provided you support my campaign to have "Iron Alloy Appreciation Week". I am still working on a pithy slogan like "Steal a moment for Iron Alloy" or "The irony of Iron Alloy" or "Iron Alloy: it is your father's alloy" or "Available for Centuries for centuries".
    May I suggest, "Iron alloy, a better use for coke."

  25. #25
    Senior Member
    Join Date
    Dec 2009
    Posts
    5,423
    Mentioned
    18 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 10 Wheels View Post
    Wear two three pairs of shorts.
    Now you see? That is truly creative. Especially appropriate if I can't get my seat post unstuck. I love it. We have a winner. No one else need apply.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •