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  1. #1
    Senior Member Jackontheroad's Avatar
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    Question how to calculate reach and stack based on the dimensions of the rider's anatomy?

    I guess there is a way to calculate reach and stack by knowing at least the length of arm, torso and inseam; also, there should be a range mainly for the stack dimension depending on if the rider plans to do road racing or endurance.

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    There are fit calculators online (you could start with Competitive Cyclist and go from there, for example) but there is a large individual component (your flexibility and core strength, etc.) so that the best you can hope for is a starting point.

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    factor in flexibility and comfort, and you're probably better off actually finding what works and getting the measurements from that point, figuring you can move the dimensions some millimeters either way.
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

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    Senior Member Jackontheroad's Avatar
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    any scientifically found formulas will be useful for what I want, and much appreciated. In the question I tried to make it clear I know there will be a range for stack depending if the rider plans to ride racing or endurance; and the same idea goes if your flexibility is snake, chameleon or bull.
    Last edited by Jackontheroad; 02-18-14 at 06:21 PM.
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    There simply aren't any. The closest rule I know of is placing the handlebars one cubit from the nose of the saddle, and even then stack and reach vary based upon how high the bar is.

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    coprolite fietsbob's Avatar
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    C.O.N.I http://www.sandcreeksports.com/coni.htm part II chapter 5

    Plumb-line thru the BB axis , behind that is setback, in front of that center is reach.
    Last edited by fietsbob; 02-18-14 at 07:38 PM.

  7. #7
    Senior Member Jackontheroad's Avatar
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    Thanks for the answers, sorry I was not clear; I am not trying to measure the dimensions on a bike. I want to find a formula or a way to calculate reach and stack based on the dimensions of the rider, length of torso and arm, etc.
    Once I scratched my nose hugging a tree.
    1986 Peugeot Triathlon, 2014 Breezer Lightning, 2015 Raleigh Tamland 2

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    I really don't think there are scientific formulas. There is one rule of thumb, like KOPS, standover clearance, fist of seatpost, heel on pedal etc. That is one cubit, the length from your elbow to the tip of your middle finger, from the saddle nose to the bars, and that will give a range of acceptable stack and reach values. Like the other rules it isn't very accurate and only a starting point. Even with scientifically derived formulas, they're still just starting points.

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    Quote Originally Posted by Crescent Cycle View Post
    I really don't think there are scientific formulas.
    Right. Any "calculator" or "formula" has to be based on the fitting principles that the one who derived the formula believes in. For example, let's take Greg LeMond's fitting principles, which include pushing the seat back quite far. That is the definition of increased setback, and this, by definition, must decrease the acceptable reach measurements. Or take the principles of some of the modern fitters, who say that the saddle should be placed so that the knee is 1-2 cm ahead of the pedal spindle. This requires less setback, or even no setback, which would increase the acceptable reach measurements. If someone thinks your saddle should be quite high relative to your leg length, then you'd want higher stack, or at least, more rise in your stem. If you have your saddle quite low, lower stack is probably a requirement. Your question, then, depends on a particular set of assumptions of what constitutes good fit and as such is not a well-formed question.

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    where is "stack" measured? from this diagram, there seems to be no definite to location for the dimension, or am I missing something?

    http://surlybikes.com/bikes/long_haul_trucker/geometry

    thanks

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    Look at the horizontal lines above and below the stack line on the diagram

    Stack is measured as the height of the center of the top of the head tube minus the height of the center of the bottom bracket. For designs like the Surly, throw in an extra half inch of stack because of the external cup headset.

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    thanks. I don't always have the imagination to learn in a vacuum!

    since posting my original question, I have finished reading Touring Bikes by Tony Oliver. excellent book and a great learning for me. unfortunately, I took it back to the library this morning so can't reference the page, but his take on "stack" was from the bottom of the fork race to the top of the stem nut (? right hardware term?) - in effect the steer tube & its hardware. maybe that's a dated or English term?

    anyway, on a steep learning curve here!

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    Quote Originally Posted by southpier View Post
    thanks. I don't always have the imagination to learn in a vacuum!

    since posting my original question, I have finished reading Touring Bikes by Tony Oliver. excellent book and a great learning for me. unfortunately, I took it back to the library this morning so can't reference the page, but his take on "stack" was from the bottom of the fork race to the top of the stem nut (? right hardware term?) - in effect the steer tube & its hardware. maybe that's a dated or English term?

    anyway, on a steep learning curve here!
    Stack and reach are simply how high above, and how far in front of, the bottom bracket the head tube sits, measured center-to-center of each part. There is no subtraction involved; it's a simple measurement. Probably this diagram is more clear than pic and description above:

    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

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    yes; more better. thanks

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