now that you understand stack and reach (and if you got to school late, you'll want to take a look at THIS thread first), i'd like to explain why certain fit bikes are made the way they are. in particular, serotta's new fit bike, guru's new DFU, and the fit bike i use - the exit cycling fit bike - all adjust in an X/Y axis. there are others as well, like tiemeyer's fit bike.
there are a couple of reasons for this sort of adjustment motif: one is protocol. i'd like to isolate a plane on which i'm working. for example, if i want to see what your correct cockpit length is, i need to lengthen the cockpit without the height of the aerobars changing, otherwise that change in height might harm my attempt to drill down on just how far your armrests, and extensions, should be in front of your saddle. when i want to determine how much your armrests should be lower than your saddle, i want to isolate this, and not have the cockpit distance growing or shrinking.
so, while it might seem intuitive for fit bikes to mimic the angularity of actual bikes, in practice a bike that adjusts only horizontally and vertically is best.
but there's a second reason for bikes that adjust in this fashion. as you might imagine, the front end of the bike moves up and down on a piston, or a set of pistons, and the saddle and the front end of the bike - the aerobars - move back and forth, as does a lathe's tailstock on a set of ways. as these assemblies move up and down, and back and forth, you could laser etch on the machinery, or even affix with adhesive tape, a rule.
so it is with the fit bike i use. there's a "pin" on the top of my fit bike that's declined 17°, making the pin a proxy for a 73° head angle. that pin is (predictably) 1 1/8" in diameter, making it exactly the diameter of a fork's steer column. you place a stem on there. or, you place a headset spacer on there. or two headset spacers. whatever you want. the stem can be whatever length and pitch you want. i prefer horizontal stems, because i want as much frame up underneath me as i can get, rather than having that space taken up by a stem that's pitched up. but, it's your choice.
then, you place whatever aerobar you want in the stem. just make sure that's the aerobar the customer wants to ride - the one on which he's comfortable. the pic of the fellow below is of ves mandaric. some of you ride mandaric bikes. i have maybe 4 of his road bikes, i always and only ride his bikes for my road race bikes. he was my master builder at QR, and he and i conspired together to design the fit bike he builds (the one i use).
then, you move the saddle fore/aft, up/down, until you get it in the right place. the exact protocol for this is for a later chapter. but, that's what you do. then, you move the aerobars back and forth until the cockpit is correct, up or down (on those pistons in the image above) until the armest drop is correct, and we can debate the proper protocol, the proper order, the point is, after the rider is positioned, you now know his fit coordinates.
but, you know more than that, if you have the right kind of fit bike. you also know, just by reading the rules - both the vertical and horizontal rules - the stack and reach of the bike that fits up underneath that rider, in that position. the numbers on that black plate on the image highest up are "reach" numbers. the numbers on this piston here are "stack" numbers. they tell me what are the stack and reach of the bike that fits up underneath the position just achieved by the rider i've just positioned.
you don't need these etched numbers on your fit bike. but if you don't have them, then you either need an "X/Y tool" or you need a 48" level, a yardstick that measures metric, and pretty deft hands. in any case, it's not that hard to generate stack and reach. it's just easier if your fit bike does it for you.
now, i'm going to stop there. there's more to say. but, who understands what i just wrote above? who doesn't understand it? i'll need to explain this again, in a different way, perhaps, and maybe this is too much in one gulp.
Dan Empfield
aka Slowman
there are a couple of reasons for this sort of adjustment motif: one is protocol. i'd like to isolate a plane on which i'm working. for example, if i want to see what your correct cockpit length is, i need to lengthen the cockpit without the height of the aerobars changing, otherwise that change in height might harm my attempt to drill down on just how far your armrests, and extensions, should be in front of your saddle. when i want to determine how much your armrests should be lower than your saddle, i want to isolate this, and not have the cockpit distance growing or shrinking.
so, while it might seem intuitive for fit bikes to mimic the angularity of actual bikes, in practice a bike that adjusts only horizontally and vertically is best.
but there's a second reason for bikes that adjust in this fashion. as you might imagine, the front end of the bike moves up and down on a piston, or a set of pistons, and the saddle and the front end of the bike - the aerobars - move back and forth, as does a lathe's tailstock on a set of ways. as these assemblies move up and down, and back and forth, you could laser etch on the machinery, or even affix with adhesive tape, a rule.
so it is with the fit bike i use. there's a "pin" on the top of my fit bike that's declined 17°, making the pin a proxy for a 73° head angle. that pin is (predictably) 1 1/8" in diameter, making it exactly the diameter of a fork's steer column. you place a stem on there. or, you place a headset spacer on there. or two headset spacers. whatever you want. the stem can be whatever length and pitch you want. i prefer horizontal stems, because i want as much frame up underneath me as i can get, rather than having that space taken up by a stem that's pitched up. but, it's your choice.
then, you place whatever aerobar you want in the stem. just make sure that's the aerobar the customer wants to ride - the one on which he's comfortable. the pic of the fellow below is of ves mandaric. some of you ride mandaric bikes. i have maybe 4 of his road bikes, i always and only ride his bikes for my road race bikes. he was my master builder at QR, and he and i conspired together to design the fit bike he builds (the one i use).
then, you move the saddle fore/aft, up/down, until you get it in the right place. the exact protocol for this is for a later chapter. but, that's what you do. then, you move the aerobars back and forth until the cockpit is correct, up or down (on those pistons in the image above) until the armest drop is correct, and we can debate the proper protocol, the proper order, the point is, after the rider is positioned, you now know his fit coordinates.
but, you know more than that, if you have the right kind of fit bike. you also know, just by reading the rules - both the vertical and horizontal rules - the stack and reach of the bike that fits up underneath that rider, in that position. the numbers on that black plate on the image highest up are "reach" numbers. the numbers on this piston here are "stack" numbers. they tell me what are the stack and reach of the bike that fits up underneath the position just achieved by the rider i've just positioned.
you don't need these etched numbers on your fit bike. but if you don't have them, then you either need an "X/Y tool" or you need a 48" level, a yardstick that measures metric, and pretty deft hands. in any case, it's not that hard to generate stack and reach. it's just easier if your fit bike does it for you.
now, i'm going to stop there. there's more to say. but, who understands what i just wrote above? who doesn't understand it? i'll need to explain this again, in a different way, perhaps, and maybe this is too much in one gulp.
Dan Empfield
aka Slowman