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  1. #1
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    Comparing bike sizes based on Stack and Reach

    Shopping around for a new frame. I'll leave out the details at the moment, as really the only things that I "think" I can accurately compare between a bike I have and the bike I am thinking about are only the stack/reach.
    Owned bike (which is very comfortable, there is room for me to get more aggressive on it) has stack/reach of 593/416
    Looking at bike (which is completely different) has stack/reach of 625/438

    Rough chart from the stack/reach calculator is here for comparison.Comparing bike sizes based on Stack and Reach-geocompare.pdf
    Deflated - buy parts to sell parts to buy more parts.. bikes are my drug of choice

    FATTrailer for the kiddo

  2. #2
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    There is a simple trig formula to figure this out. Could you list the year, size, make, and model for both bikes?


    Or, I could just send you the write-up I did for someone a few months ago, and you could copy.
    2018 Surly Karate Monkey 'dingle' speed
    2013 CAADX 105
    2012 Pinarello Quattro
    2002 Zurich LeMond

  3. #3
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    Oh, I'd like to know this.
    2016 Surly Pugsley size large
    2017? Canfield Toir size medium
    Deflated - buy parts to sell parts to buy more parts.. bikes are my drug of choice

    FATTrailer for the kiddo

  4. #4
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    Quote Originally Posted by Jason Rides Bikes View Post
    Oh, I'd like to know this.
    2016 Surly Pugsley size large
    2017? Canfield Toir size medium
    I'm going to send you what I did for my friend. If you can't make the numbers work for you, let me know. It may be a few days, I work full time and am in grad school
    2018 Surly Karate Monkey 'dingle' speed
    2013 CAADX 105
    2012 Pinarello Quattro
    2002 Zurich LeMond

  5. #5
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    Change of plan, it's too long to send. I'll just put it here.

    I did this numbers comparison for a friend of mine.

    To make a comparison, you need at least one bike that you are positive fits. She had a Giant Lust mountainbike. A Surly 1 X 1 Mountainbike, and a Giant Avail road bike. She was very petite. I cant remember. Maybe 51 or 52. She was interested in the fit of a Salsa Cutthroat, which is more or less a carbon version of the Fargo.

    Analysis starts here:

    Mountainbikes and hybrids are typically larger than road bikes because the handlebars are much closer to the bike frame, and because the overall rider position, geometry, and handling are different. There are a lot of changes with mountainbike geometry lately. Same with road bikes, to be honest. The Salsa Cutthroat is in the same neighborhood as the Lust, 1 x 1, and Avail. The Lust and 1 x 1 are approximately 1.5 cms larger, and the Avail is about 1.75 cms smaller. Generally, you would want the numbers very close, within a couple of points. If you consider the Cutthroat a mountain bike, then its a very upright MB (high stack) with a shorter reach (arm distance) than the other two. So you sit up more, and dont reach as far. But, if you think of the bike fit as being closer to a road bike, like the avail, the reach is about the same, but the bike is bigger overall.

    I would expect a road bike to be more aggressive (more of a forward position of the body) with a shorter stack, and longer reach. Stack informs torso height and position. Reach correlates to arm length. A road bike actually has a longer reach in proportion to the stack, but the bike is smaller overall, so the reach number is shorter.

    The Cutthroat combines geometries. Upright and short reach should be comfortable.

    Here are the numbers. Use the formula on the next page to calculate overall size.

    .................................................. Stack. Reach HTA (head tube angle)
    Giant Lust. (Classic Mountainbike) 56.7. 39.7. 70 deg
    Surly 1 X1. (Classic Mountainbike) 56.05. 39.86. 71 deg
    Salsa CT (drop bar mountainbike) 59.39. 37.47. 70 deg
    Avail. (road bike) 55.12. 37.08. 72 deg

    The Avail has the steepest head tube, but its pretty slack for a roadie, so its stable. The others are what youd expect, the more modern lust and CT the most slack (lowest number for Head tube angle). The Surly is an older style bike, which is why the number is 71 and not 70 or 69ish. Race roadbikes have steep headtubes, 73ish. (Fast turning, not as stable).

    Here are the calculations (next page). They are based on angles and lengths. Basically how to fit and adjust a triangular shape by adding stems and spacers to the head tube to replicate fit in different bikes.


    Pretend you added a .8 cm spacer to the headset of the first bike for a base number. Adding a spacer raises the handlebars.

    Lust:
    New Stack = 56.7 + .8 = 57.5. 57.5 will be your target amount with each stack, and adjust by changing spacers.
    New Reach: 39.7 (.8/Tan(70))= 39.41. Use this number to compare bike size.

    1x1:
    New stack = 56.05 + 1.45 = 57.5
    New Reach = 39.86 ( 1.45/Tan(71)) = 39.36 very close to the Lust.

    Salsa Cut throat:
    New Stack = 59.39 1.89 = 57.5
    New Reach = 37.47 (-1.89/(70)) =38.15. Smaller overall then the first two. More upright. Shorter reach. Might need a longer stem, on the other hand, its a drop bar bike. Which typically uses a longer stem.

    Avail:
    New Stack 55.12+2.38 = 57.5
    New Reach = 37.08 (2.38/Tan(72)) = 36.30. A lot smaller than any of them. But it is a road bike. It is supposed to be. For another road bike comparison, the number should be very close to 36.30. Or start over, 55.2 + .8 spacer... Good to do both, actually.
    Last edited by Muirenn; 08-20-2018 at 01:26 PM.
    2018 Surly Karate Monkey 'dingle' speed
    2013 CAADX 105
    2012 Pinarello Quattro
    2002 Zurich LeMond

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