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Thread: Duplication of bike position across multiple bikes?

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    Default Duplication of bike position across multiple bikes?

    Just wondering if anyone has some handy tips passed down from their Great Grandfather's on how to duplicate bike position across several bikes? I don't have too many issues with the handlebar reach and height, but the seat is a bit troublesome for my analogue mind.

    I find the string with a weight tied to measure plumb line doesn't work particularly well at all. The frames are identical in dimensions, I'm using the same saddles, cranksets and pedals across both bikes FYI.

    I have a tape measure, carpenter level, broom stick, pencil and a pair of BBQ tongs if that helps at all?

    Apologies if there is a previous post about this, please provide link gratefully...
    Riding has to be fun, and part of the fun has to be that you’re not worried about having too much technology on your bike. - Tom Ritchey

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    Default Re: Duplication of bike position across multiple bikes?

    First bike. Back wheel against a wall. Measure from the center of your cranks to the wall (A). Then measure from the tip of your saddle to the wall (B).
    A-B=setback

    Second bike. Back wheel against wall. Measure center of cranks to the wall. That number minus your setback number is where the tip of the saddle should be.

    Saddle height is from the center of your saddle (mark the same spot on both saddles) to the center of the crank.

    You may need to account for differing tire sizes.
    Got some cash
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    But we're alright

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    Default Re: Duplication of bike position across multiple bikes?

    From Dave Kirk:

    Most of us have more than one bike and I often hear from riders who say that they have a hard time getting two bikes to have the same exact contact points. The three contact points, and how they relate to one another, are what determine how one sits on the bike...they are the only things that matter. It can be easy to get confused trying to balance a different seat angle and a different top tube length but there is no need to go in that direction. The only things that matter are the three contact points and how they relate to each other.

    It seems like getting good solid numbers is part science, part art, and part black magic but itʼs very simple. The trick is to reference the three points (bottom bracket, saddle, and handlebar at stem) to each other and the easiest way to do that is by referencing these points to the floor and a wall.

    I will throw this caveat out there before outlining the process if you are using different saddles, handlebars or crank lengths then you can have a hard time and it will be an apples-to-oranges comparison at best. That said
    We need to start with a ʻhome baseʼ if you will and that will be the bottom bracket everything springs from the bottom bracket. Hereʼs what you can do -


    1) Saddle height most riders know how to get this number but just in case...you want to measure from the BB center along the center of the seat tube and up to the upper surface of the saddle. Itʼs important that the tape be held inline with the seat tube centerline to get a solid number. Write down this number.

    2) Saddle setback or fore/aft position typically people try to do this with a plumb bob hung off the nose of the saddle but this can be really tricky to get just right. The following way is much easier and more accurate.
    a. First you want to place the bike standing next to a wall and back it up into a corner so that the rear tire is up against the adjacent wall. This will allow you to measure the saddle and BB to the rear wall. So first hold your tape horizontally between the rear wall and the BB center. Itʼs key that the tape is more or less horizontal but you need to be WAY off level for this to have a large effect. Get it fairly level and you are good to go. Write this number down.
    b. Next measure horizontally from the nose of the saddle rearward to the wall holding the tape horizontally. Write this number down.
    c. Now simply subtract the saddle-to-wall number from the BB-to-wall number and you have an accurate saddle setback number.

    3) Cockpit or saddle-to-bar reach This one couldnʼt be simpler. Hold the end of the tape against the nose of the saddle and measure to the bar center where it enters the stem. The bar centerline is typically the slot between the main part of the stem and the faceplate so itʼs easy to find. Write this number down.

    4) Bar drop or saddle-to-bar drop this time we are going to reference to the floor to get an accurate number.
    a. First measure from the saddle straight down to the floor. For the sake of consistency you should measure from the lowest part of the center of the saddle (often called the hammock) to the floor. Write this number down.
    b. Now measure from the center of the handlebar where it enters the stem directly to the floor and write this number down.
    c. Now to get the actual bar drop do the math and figure out the difference of the saddle-to-floor compared to the bar-to-floor numbers. This is your saddle to bar drop.

    Now you have four numbers (saddle height, setback, cockpit length and bar drop) that will allow you to set up bike B to fit just like bike A...or at a minimum have a real understanding how the two differ. Note that there isnʼt a single reference to seat tube or top tube length, head tube length or seat angle as these really do confuse the matter when trying to define the location of the three contact points.

    With these four numbers in hand whatʼs next? Well if you are trying to set up bike B exactly like bike A youʼll no doubt need to start moving stuff and I suggest you do it in the same order that you took the above measurements. Start with saddle height and then move to setback and then to cockpit and finally bar drop. Note that you will no doubt need to go back and tweak one setting after making the second adjustment and it could take a few rounds of back and forth to get them both to be right. Setting the cockpit length can mess with the drop and visa-versa so you will need to no double check, tweak, and recheck a number of times to get everything in the right place. One place many will have issues it with the cockpit length and this is because stems come in fixed lengths typically in 10 mm increments so judgment calls often need to be made and you need to decide if you want to be a few millimeters longer or shorter.

    I hope you find this helpful in getting an accurate set up of your contact points. Once you get used to it you can set up bikes very quickly this way even rental bikes can be tweaked quickly in a hotel room easily using this method. There are no doubt other ways to do this I find this works well for me. I hope it does for you.

    dave





    I have this printed out in my workshop. Has worked well for me. As referenced within and by Chase, contact points (saddle, etc.) and tire size need to be the same to get this exact. Otherwise, the best you'll do is 'pretty close'. Also measure both bikes with the same device/tape to avoid another source of variability.
    Lou D'Amelio
    Bucks County PA

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    Default Re: Duplication of bike position across multiple bikes?

    t square + masking tape on the wall. You only have to dial the tape positions based on the crank height difference.
    Last edited by sk_tle; 09-10-2020 at 06:27 AM.
    --
    T h o m a s

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by sk_tle View Post
    t square + masking tape on the wall.
    If by t square you mean drywall square then yes. Short bit to stand on the floor and the long arm up the wall to measure to/from.

    drywall square.jpg

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    Default Re: Duplication of bike position across multiple bikes?

    I use a plumb and tip of the saddle. When learning how to do this many years ago, I didn't have a convenient place that I use for the wheel-against-the-wall method.

    Are bar positions identical across the 2 bikes? if so, saddle position should be simple. Since saddles and frames are the same, center of bb up along ST to top of saddle. However, for that to be accurate, saddle angle must be the same. The only way I know how to do this is accurately is with an angle finder and a clipboard that will sit atop the front and rear of the saddle. For me, this is especially important if using something like a Power or Romin-type saddle, where the seating surface isn't flat. Once you get angle correct, you can be fairly confident in saddle height, assuming setback isn't crazy off. If you're using the same bar/ stem, it's easy enough to measure from bar to tip of saddle to get setback where it needs to be.

    To be honest, angle finder, tape measure, long level (for bar drop), and a plumb are what I prefer. And https://www.abbeybiketools.com/produ...nt=39515341962. This little device from Abbey is really, really handy.
    Last edited by dashDustin; 09-10-2020 at 09:26 AM.
    -Dustin

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by dashDustin View Post
    ..... And https://www.abbeybiketools.com/produ...nt=39515341962. This little device from Abbey is really, really handy.
    Plus one on the Abbey Fit Kit.
    Easy to use. Very repeatable.
    It defines a point of reference from which everything can be measured and set the same.
    Mark Walberg
    Building bike frames for fun since 1973.

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by Bingissimo View Post
    If by t square you mean drywall square then yes. Short bit to stand on the floor and the long arm up the wall to measure to/from.

    drywall square.jpg
    I"ve been looking for one of those ever since I tried to duplicate my fit on my old Foil on my Felt AR. I may need to do something similar in the near future again (duplicate fit on my AR to either an Axiom or Alchemy Eros). How much is one of these things? Also, is there one that's slideable? I think my fitter has something similar, but that thing is like $250...

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by echappist View Post
    I"ve been looking for one of those ever since I tried to duplicate my fit on my old Foil on my Felt AR. I may need to do something similar in the near future again (duplicate fit on my AR to either an Axiom or Alchemy Eros). How much is one of these things? Also, is there one that's slideable? I think my fitter has something similar, but that thing is like $250...
    $18 at Harbor Freight instore only

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by echappist View Post
    I"ve been looking for one of those ever since I tried to duplicate my fit on my old Foil on my Felt AR. I may need to do something similar in the near future again (duplicate fit on my AR to either an Axiom or Alchemy Eros). How much is one of these things? Also, is there one that's slideable? I think my fitter has something similar, but that thing is like $250...
    They're pretty cheap, at Home Depot/Lowes/etc:
    https://www.homedepot.com/p/Empire-4...0-48/202035306

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    Default Re: Duplication of bike position across multiple bikes?

    Sweet. Thank you both.

    Someone actually mentioned these things back two years ago. I thought I was literally buying a square slab and didn't follow up on it. This thing could be quite useful, for so many things.

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    Default Re: Duplication of bike position across multiple bikes?

    Having multiple bikes to fit, my biggest caveat is if you have different saddles. Two saddles that are both 30cm long may have a couple cm different spot where the sit bones sit relative to where the nose of the saddle is. Trust me, been there done that with the nose of the saddle and its relationship to center of bb.

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by Moke View Post
    Having multiple bikes to fit, my biggest caveat is if you have different saddles. Two saddles that are both 30cm long may have a couple cm different spot where the sit bones sit relative to where the nose of the saddle is. Trust me, been there done that with the nose of the saddle and its relationship to center of bb.
    I was going to say the same thing. The latest Fizik saddles I have place a mark where the width equals 75 or something like that. Makes it easier to approximate setback--especially if the nose of the saddle has been chopped off, as found in recent models (Pro Stealth, Fizik Argo). You can approximate it that way (measure width of saddle A & B) or place (unmounted) saddle A on top of mounted saddle B and match their width profiles. A French fitter I'm familiar with also measures where the dip of the saddle falls because that (along with width) influences the sweet spot where you settle in.

    Long story short, approximate in the lab/shop, then go ride with an allen wrench. Ride some more. And not everyone thinks every bike has to have the exact same fit/set up.
    am I the only Marvin?

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by giordana93 View Post
    And not everyone thinks every bike has to have the exact same fit/set up.
    This x 10. Same set up makes sense for similar bikes for identical use, but you may want different fits for different purposes. I use less drop on my mega-miles lugged steel bike as opposed to a race fit (more drop and slightly more reach) on my ex race bike, etc. Sameness is not always a virtue.
    Lou D'Amelio
    Bucks County PA

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by ldamelio View Post
    This x 10. Same set up makes sense for similar bikes for identical use, but you may want different fits for different purposes. I use less drop on my mega-miles lugged steel bike as opposed to a race fit (more drop and slightly more reach) on my ex race bike, etc. Sameness is not always a virtue.
    For road and gravel bikes, I'm in the camp of every saddle in the same spot but the bars have some wiggle room depending on the bike and use.
    "I guess you're some weird relic of an obsolete age." - davids

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    Default Re: Duplication of bike position across multiple bikes?

    Quote Originally Posted by chasea View Post
    First bike. Back wheel against a wall. Measure from the center of your cranks to the wall (A). Then measure from the tip of your saddle to the wall (B).
    A-B=setback

    Second bike. Back wheel against wall. Measure center of cranks to the wall. That number minus your setback number is where the tip of the saddle should be.

    Saddle height is from the center of your saddle (mark the same spot on both saddles) to the center of the crank.

    You may need to account for differing tire sizes.
    +1 on this method, I find it easier than the drywall square.

    I use my garage door frame. An old inner tube is tied to the track, I loop this around a pedal to hold the bike upright and firmly against the vertical.

    Other tip is to make peace with the concept of accuracy vs. precision. Getting the saddle in the right place does not necessarily mean getting it within 0.5 mm of your other bike.
    Trod Harland, Physical Educator

    Not everything that is faced can be changed, but nothing can be changed until it is faced. — James Baldwin

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    Default Re: Duplication of bike position across multiple bikes?

    Follow-up question

    For the T-square / drywall square, is it better to use the rigid ones shown above or an adjustable one (say at 15 deg increments). For whatever reason, while the latter would seem to be more useful, I do wonder about screws wearing out, etc.

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