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Thread: Time Frames Geometry

  1. #1
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    Default Time Frames Geometry

    alright, so I'll admit that between looking around for a replacement for my 16 year old Giordana that's had me glancing at the Time frames at justin's site, and triskie's discussion about stem length that mentioned her cervelo, I'm intrigued by the use of a 73 sta in all the time and cervelo frames, regardless of size. what gives? are they just assuming that some riders will go with a zero-setback post, especially in the smaller sizes? or that even small riders might need 6+ cm of saddle setback?
    I seem to recall someone trashing cervelo for not offering more size-specific angles, but doesn't Time do the same thing? is there any method to this madness, or is it just cost-saving (ahem, hard to believe with the prices for those frames, both made in France and in Taiwan or China). so for all the cervelo-hating Time lovers, how do you solve this paradox? sorry for the lame baiting, but it's gotta start somewhere
     

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    the 73 degree thing is just some ill thinking on their part. but a broken clock is right twice a day so it works for some. they'll tell you they used military studies on leg length and that 73 degrees works for all, especially if you flip the seatpost backwards...
    they wont tell you that those studies were commissioned to develop pants sizing and not for bike sizing.


    seat tube angle is a funny thing... its odd to single it out because it doesn't mean anything until you set the saddle (after you set the cleats and determine your crank length). its just for most short folks 73 degrees isn't steep enough... if you have short femurs and ride long cranks its impossible.

    so, if it works for you its great and if it doesn't its silly. but seat tube angle is just one aspect of the whole thing. having one seat tube angle through the entire range of bike sizes ...
    defies logic.

    marketing it as science is brilliant.


    time has sensible geometry. they get it.
    shrink, terrorist, poet, president of concerned cyclists for the abolishment of bovine source bicycle parts and head of the disaffected commie dishwashers union.

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    Quote Originally Posted by Flux View Post
    g93

    take into consideration that the size XXS and XS have 74.7 and 74 deg seat angles respectively. also sizes XXS, XS and S have 71.5, 72 and 72 again headtube angles.

    cheers,
    justin
    well, doh, that would explain some of it; I hadn't looked at a recent geometry chart, just remember being struck by the 73 across the board, but obviously that's not the case. (hey, why let a little research and reality get in the way of a good rant/gut feeling?) we're still free to rant about cervelo, though, right?

    just checked and a few of the modules are at 73.5 in the XS; still pretty laid back for a 51 or so, no?
     

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    Quote Originally Posted by swoop View Post
    so, if it works for you its great and if it doesn't its silly. but seat tube angle is just one aspect of the whole thing. having one seat tube angle through the entire range of bike sizes ...
    defies logic.

    marketing it as science is brilliant.


    time has sensible geometry. they get it.
    not to prolong this for no good reason, but here's the rub: time uses 73 for 4 of 6 sizes (S-XL), and on over half of the models, a 73.5 on the XS, but "they get it". Cervelo is 6 for 6 and they defy logic, are silly, etc.
     

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    I'm in the same boat fit wize... I don't need nearly the set back that 73' can provide.

    But that said, any contact points can be made to work the right post, but the wheelbase
    is something you can't work around. A frame with a sub 54cm top tube, and a 73' seat angle
    is going to have a wicked short wheelbase, unless you super slack the head angle.
    It makes no sense. atmo, ymmv, etc etc...

    -g
     

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    over half is not all. that's the difference. that 73 covers many.. but not all. and shouldn't be all. that is the difference. yes. you got it.
    shrink, terrorist, poet, president of concerned cyclists for the abolishment of bovine source bicycle parts and head of the disaffected commie dishwashers union.

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    Quote Originally Posted by GrantM View Post
    A frame with a sub 54cm top tube, and a 73' seat angle
    is going to have a wicked short wheelbase, unless you super slack the head angle.
    It makes no sense. atmo, ymmv, etc etc...

    -g
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    Quote Originally Posted by swoop View Post
    over half is not all. that's the difference. that 73 covers many.. but not all. and shouldn't be all. that is the difference. yes. you got it.
    well now I'm convinced because you said so.

    dialogue: a discussion between two or more persons or groups, esp. one directed toward exploration of a particular subject or resolution of a problem
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    Last edited by giordana93; 03-26-2009 at 08:07 AM. Reason: added frame legend
     

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    74.5
    73.5

    world of difference!

    wish cervelo would adapt that for the shorties.
    shrink, terrorist, poet, president of concerned cyclists for the abolishment of bovine source bicycle parts and head of the disaffected commie dishwashers union.

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    cervelo designs in the small sizes make no sense atmo. think of it this way: is everyone else wrong? or is it really just this easy to design a bike? hmmm.
    Qui plume a, guerre a. Ce monde est un vaste temple dédié à la discorde.

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    Quote Originally Posted by dbrk View Post
    cervelo designs in the small sizes make no sense atmo. think of it this way: is everyone else wrong?

    Actually, that's pretty much what they're saying.

    http://www.cervelo.com/content.aspx?...=WhitePapers#1

    Here's the thing: Cervelo is saying it's a better idea to move bars to the rider,
    instead of the rider to the bars. The fundamental problem with Cervelo's solution
    is that it changes the wheelbase of every side of their bike. Bad Idea. Capital B Capital I.
    Catch me on a snarky mood day, and i'll tell you that all that really matters is wheelbase
    and trail, and I'll fit the rest with posts and stems... So in a word, I think Cervelo is
    just nuts. They can say whatever they want about "their Pro's ride it" (like what other
    choice do they have?)

    Here's the super-irony.... Cervelo is the company who more than anyone has broken
    the whole Saddle-Pedal set back paradigm.... they're the fast-forward company for
    crying out loud.... If a triathlete can pedal like the wind in the super forward position, why
    is the ONLY solution for a road customer a 73' seat angle? Every tri rider is moved forward,
    but for some reason it's a sin on a 5 foot tall road bike?

    -g
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    I'm not sure I see the need for a steeper head-tube angle, which seems to also be a tenet of the Cervelo design for small frames.

    I've also always wondered, why do the head tubes on giant bikes seem to be so steep? Or is it just because the seat tube angle has to be more slack/shallow for taller riders?
     

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    agreed (with Grant), but here's the other side of the story. in most bikes of the smaller sizes, the sta can be close to 75. there is no way (for me at least) to get enough set back on a 52 with a 75 sta, without perhaps hunting down a wacko set back seat post that would leave my weight hanging way back over the rear wheel. the more typical rider of a 52 might be happy. on the other hand, a 73 works for me using a normal (25mm) set back post. put a zero set back post on the 73 and you can accommodate a good deal more riders. so which is the worse compromise, a zero setback post for some folks on the 73 (not too hard to track one of those down), leaving weight still about where a steeper sta would, or a no-go or an uber set back post on a 75? especially if we admit that riders of small bikes should get the opportunity to try a position a couple cm behind kops like everybody else? and don't answer "get a custom frame"--that is not the question. and how does one refute cervélo's claims on these slides of the same paper grant cited?
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    I'm 5' 8" and my bikes have about a 75 degree sta. I can do 74 on a no setback post. I could also ride shorter cranks but I'm not going to undo all these years of preferring 172.5s.

    That's the other modern problem, the restriction of size options to keep manufacturing prices down.
    shrink, terrorist, poet, president of concerned cyclists for the abolishment of bovine source bicycle parts and head of the disaffected commie dishwashers union.

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    swoop and giordana93 i'm not feeling this yet. i don't measure the
    frame angles but am aware from the setback that they are steep
    in the small sizes. would you two know what the saddle nose behind
    the bb center distance is on your bicycles? mine is 5cm with an aspide
    saddle, a 14.5cm frame setback on a 54cm, and a setback seatpost.
    i'd wager the sta is at least 74.5 on my frame atmo.

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    the thing about cervelo is that they spend so much energy telling you that no matter what ///the pants you are buying from them must fit...
    cause you bought them from them...
    and nobody elses can fit...cause you bought them from someone else.
     

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    4cm on an arione. 71.5 to saddle top. I'm a hobbit with long shins.
    shrink, terrorist, poet, president of concerned cyclists for the abolishment of bovine source bicycle parts and head of the disaffected commie dishwashers union.

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    Quote Originally Posted by e-RICHIE View Post
    swoop and giordana93 i'm not feeling this yet. i don't measure the
    frame angles but am aware from the setback that they are steep
    in the small sizes. would you two know what the saddle nose behind
    the bb center distance is on your bicycles? mine is 5cm with an aspide
    saddle, a 14.5cm frame setback on a 54cm, and a setback seatpost.
    i'd wager the sta is at least 74.5 on my frame atmo.
    I'm at 4.5cm back... 68.5 saddle height.

    I'll do 75' on my next frame, so i can slide the seat 5mm further back on the rails
     

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    frame setback is all about putting the rider in the right place and the wheels in the right place. if you have too much setback in the smaller sizes without making the top tube longer the front center ends up being stupid short....like on a 48cm and 51cm cervelo and the bike rides like shit. likewise if you put too little setback on a big bike like a 61cm top tube without making the top tube stupid shorty you end up with too long a front center and the bike rides like shit.

    for this reason every single person on csc regardless of size, rode 54s, 56s or 58s. the 61, 48 and 51cm frames sucked.

    companies that design bikes based on "fit" are doomed to design bikes that ride like shit. if you're only smart enough as a product manager to take one criteria into account....for god's sake pick front center and trail and make the rest of the bike work within the specifications of the shimano components you're buying by the container load....at least then the chainstays won't be too short or too long and the brakes, cranks and gears'll all be in the right place.

    jerk
     

  20. #20
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    Quote Originally Posted by swoop View Post
    That's the other modern problem, the restriction of size options to keep manufacturing prices down.
    bingo. it's again what percentage of the population can be "made to fit" on the fewest possible number of offerings

    re: Richard, we get hung up on these angles because manufacturers usually don't include what you framebuilders measure as the frame setback and it's a trial and error process to figure out how the one number (sta) translates into the other (frame setback). I'd love a custom frame and will spring for one one of these days, but I'm still sorting out my contact points--after 30 years, but the last decade has seen a precipitous falling off of annual mileage so I'm second guessing some things I took for granted, starting with seat height which dictates a whole host of others (I've been low but way back, now trying out higher, more forward, yada yada)
     

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