Top-tube length and seat-tube angle: Are Colnago's 56 and 57cm frames the same?
Results 1 to 14 of 14
  1. #1
    RoadBikeReview Member
    Reputation:
    Join Date
    Dec 2001
    Posts
    208

    Top-tube length and seat-tube angle: Are Colnago's 56 and 57cm frames the same?

    I noticed this today looking at Ernesto's geometry chart: A size 56 has a 55cm top-tube and a 73.5 degree STA, while his size 57 has a 55.6cm top tube but with a 73 degree STA.

    Doesn't this make both frame's reach the same?

    So the only real difference is the standover (who cares), and head tube height, right? Unless the HTA is steeper on the 56. Does anyone know if this is the case?
    Last edited by yzfrr11; 03-28-2005 at 11:54 AM.

  2. #2
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    10,153

    same reach...

    The reach is the same within 1mm and so is the front-center, so essentially the 57cm is just taller, not longer.

  3. #3
    RoadBikeReview Member
    Reputation:
    Join Date
    Mar 2002
    Posts
    577
    Am I looking at seat angle wrong? I thought 73 would angle the seat farther back. The angle is measured from the top tube and the inside of the seat tube, so wouldnt 90 be strait up and the lower the angle the more rearward the seat?

  4. #4
    eminence grease
    Reputation: terry b's Avatar
    Join Date
    Jan 2004
    Posts
    18,538
    Quote Originally Posted by jtompilot
    Am I looking at seat angle wrong? I thought 73 would angle the seat farther back. The angle is measured from the top tube and the inside of the seat tube, so wouldnt 90 be strait up and the lower the angle the more rearward the seat?
    In order to maintain the same position (knee to pedal spindle) you have to move the saddle forward which negates the increase in the top tube.

  5. #5
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    10,153

    reach...

    Quote Originally Posted by jtompilot
    Am I looking at seat angle wrong? I thought 73 would angle the seat farther back. The angle is measured from the top tube and the inside of the seat tube, so wouldnt 90 be strait up and the lower the angle the more rearward the seat?
    Subtract the seatback (Scc) from the TT length and you get the "reach" of the frame. To be totally accurate, the frames should be the same size, but the 1cm size difference makes little difference. The diference in reach tells you how much of a stem length change would be required to produce the same fit, with the saddle in the SAME place, relative to the BB. Changing the STA does not mandate a change in saddle position.

  6. #6
    RoadBikeReview Member
    Reputation:
    Join Date
    Jul 2002
    Posts
    154
    what c40 said. ignore the sta. it's an irrelevant number. the setback is what you want to know. most euro builders dont build from a sta, but rather a setback, and then figure the sta from there. that's why a lot of euro bikes (colnago, pegs, etc) have weird sta, like 73.3 degrees and such.

    dont ignore the importance of balance though. colnagos are designed to be ridden with a long low stem and with your ass hanging over the rear wheel.
    "When they kick at your front door, how you gonna come?
    With your hands on your head or on the trigger of your gun!"

  7. #7
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    10,153

    another myth...

    [QUOTE= colnagos are designed to be ridden with a long low stem and with your ass hanging over the rear wheel.[/QUOTE]


    Folks keep quoting that baloney about Colnagos, but with relatively steep STAs and the standard Colnago seatpost, the rider won't be any further back than any other bike. In sizes below 56cm, the TTs are as long as most othesr, so the stem length required won't be particularly long. Only the larger sizes have a bit shorter than average TT lengths.

    LOOK's traditional geometry is more laid back with shorter TT lengths.

  8. #8
    RoadBikeReview Member
    Reputation:
    Join Date
    Dec 2001
    Posts
    208
    Quote Originally Posted by C-40
    The reach is the same within 1mm and so is the front-center, so essentially the 57cm is just taller, not longer.
    Actually, according to your formula: reach = [TT] - [set-back]

    For size 56: TT = 55.0 and set-back = 15.3; so [55.0] - [15.3] = reach of 39.7

    For size 57: TT = 55.6 and set-back = 16.1; so [55.6] - [16.1] = reach of 39.5

    So, Ernesto - your 57cm frame is actually smaller than your 56cm frame. Good work Ernie!
    Last edited by yzfrr11; 03-29-2005 at 06:19 AM.

  9. #9
    banned
    Reputation: colker1's Avatar
    Join Date
    Jan 2003
    Posts
    7,890
    [QUOTE=C-40]
    Quote Originally Posted by colnagos are designed to be ridden with a long low stem and with your ass hanging over the rear wheel.[/QUOTE


    Folks keep quoting that baloney about Colnagos, but with relatively steep STAs and the standard Colnago seatpost, the rider won't be any further back than any other bike. In sizes below 56cm, the TTs are as long as most othesr, so the stem length required won't be particularly long. Only the larger sizes have a bit shorter than average TT lengths.

    LOOK's traditional geometry is more laid back with shorter TT lengths.
    actually there's a grain of truth in the long stem colnago legend: their front centers per given size are longer and top tubes are shorter due to the slack head angle. a rider can pick a one size smaller bike and have his wheelbase covered. thye longer stem will place his weight over the front axle as he is used to.. i suspect the slacker front angle makes the increased drop over the front give an aero position but not a twitchy dangerous ride. .

  10. #10
    RoadBikeReview Member
    Reputation:
    Join Date
    Mar 2002
    Posts
    577
    Well, if your using that formula a 53, 54, 55, 56,57, are all about the same. So whats the point? A 53 is the same size as a 57?

  11. #11
    eminence grease
    Reputation: terry b's Avatar
    Join Date
    Jan 2004
    Posts
    18,538
    Quote Originally Posted by C-40
    Changing the STA does not mandate a change in saddle position.
    Now you have me confused - if making the STA slacker (73.5 to 73) puts the center of the post (as a point of reference) back Xcm, the saddle doesn't need to come forward that same Xcm to maintain your reference point to the pedal spindle?

    In this example, the 56 with a 73.5 gives you a setback of 15.90. The 57 with a 73 gives you 16.66. If you wanted the same (let's say) 75mm setback (BB center to saddle tip) you'd have to move the saddle forward on the 57 by .77cm to get there, no?

  12. #12
    RoadBikeReview Member
    Reputation:
    Join Date
    Dec 2001
    Posts
    208
    Quote Originally Posted by jtompilot
    Well, if your using that formula a 53, 54, 55, 56,57, are all about the same. So whats the point? A 53 is the same size as a 57?
    Don't forget though, in order to directly compare reach for frames with different head tube lenghts, you have to subtract (cos[HTA] * [spacers]) from the reach value to account for the spacers that you use.

    So, if you add stem spacers to a small frame so that the stack hight is equal to a larger frame, the total reach will be smaller.

  13. #13
    RoadBikeReview Member
    Reputation:
    Join Date
    Dec 2001
    Posts
    208
    So, the final formula for reach would be:

    reach = ([TT] - [set-back]) - (cos[HTA] * [spacers])

  14. #14
    RoadBikeReview Member
    Reputation:
    Join Date
    Jul 2002
    Posts
    154
    bs. colnago's most certainly want a long low stem. read the coni manual. it's about handling, not fit. you can fit just about anyone to just about anything with the right combination of stem, bars, seatpost, and saddle. doesnt mean it's going to handle worth a damn.

    now ... sure ... you can put whatever stem you want on a colnago. like i care if some schmoe sets up his c50 with a 90mm stem pointed skyward. obviously the bike is still rideable. doesnt mean it's 'correct' or that the bike will handle like it's supposed to.
    "When they kick at your front door, how you gonna come?
    With your hands on your head or on the trigger of your gun!"

Posting Permissions

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

THE SITE

ABOUT ROADBIKEREVIEW

VISIT US AT

© Copyright 2019 VerticalScope Inc. All rights reserved.