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  1. #1
    LOOK lover
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    Question Calculating correct stem length...

    I've got a 10cm stem on my 54cm C'dale CAAD7. Would I want the same size stem to duplicate the fit on a 53cm LOOK 585? Both frames have identical TT length (54.5cm, although that's a virtual measurement on the slightly sloping LOOK) and ST and HT angles (73.75 and 73 degrees, respectively), but the 148mm HT on the LOOK is a tad taller than the 146mm HT on the C'dale. Is it just a matter of comparing the TT lengths?

    I feel like I've got a good position dialed in on the C'dale - nice and compact, great for crits. I'll use the LOOK for road races, though, and wouldn't mind being just a tad more comfy for those 50-70 milers - but I don't want to do anything to compromise my climbing or sprint positions.

    Thanks!
    Last edited by BugMan; 08-23-2005 at 06:59 PM.
    "Tact is the knack of making a point without making an enemy." -- Howard W. Newton

  2. #2
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    Looks very close from a geometery standpoint so you should be close enough. Handlebar reach varies from model to model as does saddle setback so watch these components closely if you want to duplicate the fit between the two bikes.

  3. #3
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    sure about the 53???

    The TT length on the LOOK is a true horizontal measurement, just like the C'dale. Both are 54.5cm, but the LOOK has a very slightly steeper 73.75 degree STA. This makes the LOOK TT length 2mm longer, or 54.7cm.

    The only other thing to consider is not just the head tube length, but the total head tube length with the headset and spacers installed. That's what you want to be the same. The LOOK will come with a headset that adds 15mm to the HT length, for a total of 163mm, with no spacers. You should compare this length to you C'dale.

    A 10cm stem is pretty short for a race bike.

    I'd consider the smaller 51cm LOOK 585 which would have a comparable TT length of 53.9cm (after correcting for the difference in the STA). Whether this is a desirable alternative depends on the handlebar height that you need. The 51cm has a 2.3cm shorter head tube.

    If you measure the height of your handlebars from the floor to the top of the bars, I can give you some stem angle and spacer options with either frame.

    FWIW, the 51cm frame with 2cm of spacer (the most I'd use) would produce a handlebar height of approximately 88.5cm with an 84 degree stem. The same height would be produced by flipping the stem with no spacers, but the stem should be 10mm longer if it's used in the flipped position.

  4. #4
    LOOK lover
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    Quote Originally Posted by C-40
    The TT length on the LOOK is a true horizontal measurement, just like the C'dale. Both are 54.5cm, but the LOOK has a very slightly steeper 73.75 degree STA. This makes the LOOK TT length 2mm longer, or 54.7cm.
    It's not clear from the diagram on LOOK's website if TT length is a real or virtual measurement, but the diagram on Competitive Cyclist's website suggests it's a virtual measurement. The 53cm frame has a 35mm slope.

    Also, as far as I can tell both the 54cm CAAD7 and the 53cm 585 have the same ST angle (73.75 degrees).

    My C'dale measures 89.9 cm from floor to top of handlebars using the 10cm stem (80 degree rise) and 2.5 cm of spacers. It also has an integrated FSA headset that looks to add about 15mm to the HT length.

    In case it matters, the two stems I'm considering have 82 and 84 degrees of rise. I really don't like the looks of stems in the flipped position. Of course, if a different rise would result in a better fit I'll gladly change.

    Thanks again -- ted
    "Tact is the knack of making a point without making an enemy." -- Howard W. Newton

  5. #5
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    virtual is real...

    The term "virtual" is meaningless, it's meant to imply horizontal. LOOK measures their TT length horizontally, just like a non-sloping frame. The only other (worthless) measurement that some manufacturers provide is the TT length along the center of the sloped TT.

    What you still need to do is measure from the bottom of the headset to the top of the spacer stack to compare these frames.

    If you used an 84 degree stem instead of an 80 it would raise the bars almost 1cm.

    The 51cm would provide an 89cm bar height, but only with 2.5cm of spacer and an 84 degree stem.

    If it was me, I'd base part of the decision on saddle height. If you saddle height is over 72cm, I'd go with the larger frame. If it's 72cm or less, it says you're using a conservative bar height.
    Last edited by C-40; 08-24-2005 at 04:35 PM.

  6. #6
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    Okay, here are the C'dale measurements:

    Bottom of headset to top of spacer stack: 35 mm
    Bottom of headset to top of stem cap: 70 mm
    Floor to top-center of saddle: 97.5 cm
    Floor to top of handlebar: 89.9 cm

    ted
    "Tact is the knack of making a point without making an enemy." -- Howard W. Newton

  7. #7
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    wrong meaurement..

    Quote Originally Posted by BugMan
    Okay, here are the C'dale measurements:

    Bottom of headset to top of spacer stack: 35 mm
    Bottom of headset to top of stem cap: 70 mm
    Floor to top-center of saddle: 97.5 cm
    Floor to top of handlebar: 89.9 cm

    ted

    From the bottom of the headset, I meant the bottom at the fork crown! The idea is to compare the total head tube length with the headset and spacers. It should be about 180mm if the head tube is 146.

    FWIW, your saddle is .5cm higher than mine and your bars are 2cm higher.

    From what you've posted, I know you've got a stem with only 35mm clamp length. A person who want's a fairly high handlebar should be using an 84 degree sten with a 40mm clamp length, like a Ritchey or Easton. This will reduce the spacers by up to 15mm.

    With an 84 degree stem, you need a total stack height of 165mm from the fork crown to produce the 89cm bar height. This would require 25mm of spacer on the smaller frame and no more than 5mm on the larger frame. It's kind of a toss-up. There's a big jump of 4.5cm in the seat tube length between these frame sizes. With the larger frame, you won't have a lot of post showing, even though the TT slopes. A 250mm post should be long enough.

    The smaller frame will require a longer 350mm post and one size longer stem than your C'dale.

    If there's any chance you want the bars higher than 89cm, then the larger frame would be the best choice.

  8. #8
    LOOK lover
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    Thanks, C-40.

    Yes, total length of head tube+spacers+headset is 181 mm.

    Bar height on my C'dale is already close to 90cm, so I think I'll go with the 53cm frame, 10cm stem, and 250mm post.
    "Tact is the knack of making a point without making an enemy." -- Howard W. Newton

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