"Is there a ratio of stack:reach that says a bike is long/low or tall/narrow."
it's not hard to divine. in very rough terms, if the stack of a bike is more than a third again its reach, it's starting to trend narrow/tall. so:
reach of 36cm x 1.33 = stack of 47.9cm
reach of 38cm x 1.33 = stack of 50.5cm
reach of 40cm x 1.33 = stack of 53.2cm
reach of 42cm x 1.33 = stack of 55.8cm
reach of 44cm x 1.33 = stack of 58.5cm
so, while a ratio of 1.33 or greater means it's trending narrow/tall, i think a ratio of 1.22 or smaller means it's trending long/low.
reach of 36cm x 1.22 = stack of 43.9cm
reach of 38cm x 1.22 = stack of 46.4cm
reach of 40cm x 1.22 = stack of 48.8cm
reach of 42cm x 1.22 = stack of 51.2cm
reach of 44cm x 1.22 = stack of 53.7cm
again, very general numbers. so, you take a bike that's got a reach of 42.0cm, if it's got a stack between 51.2 and 55.8 its a relatively mainstream bike, geometrically, at least as regards fit. let's see how some of these line up. here are bikes with a roughly 42cm reach, with their stack numbers, in order of long/low to narrow/tall:
kestrel airfoil pro size 52 reach 41.5cm stack 48.4cm ---- ratio: 1.17
kuota kueen k size 54 reach 50.3cm stack 42.6cm ---- ratio: 1.18
cervelo p3 size 54 reach 41.9cm stack 49.8cm ---- ratio: 1.19
cervelo p2 size 54 reach 41.8cm stack 51.2cm ---- ratio: 1.22
felt size 56cm reach 42.5cm stack 52.5cm ---- ratio: 1.23
orbea ordu size 57 reach 42.2cm stack 53.0cm ---- ratio: 1.23
argon18 E114 size M: reach 41.9cm stack 51.5cm ---- ratio: 1.23
qr cd0.1 size M reach 42.0cm stack 49.7cm ---- ratio: 1.26
trek speed concept size L reach 42.6 stack 54.1 ---- ratio: 1.27
specialized transition size XL reach 42.1cm stack 54.2cm ---- ratio: 1.29
cannondale slice size 58 reach 41.7cm stack 54.8cm ---- ratio: 1.31
scott plasma size L reach 41.6cm stack 54.8cm ---- ratio: 1.32
BH gc aero reach 42.0cm stack 56.0cm ---- ratio: 1.33
blue triad size ML: reach 41.4cm stack 55.8cm ---- ratio: 1.35
now, there are certain things to remember:
1. these bikes to not necessarily maintain these ratios throughout their size runs. for example, on our home page are write-ups of kestrel's 4000, and with its two tri bikes (the 4000 and the airfoil pro) plotted against trek's speed concept. the speed concept keeps to its ratio. the two kestrels do not. this is not a bad thing, it's just a notable thing, and it gives kestrel's retailers a pair of geometric styles to choose from when fitting their customers. just, neither model keeps to a single style. they're BOTH moderately trending long/low in their two largest sizes. but in their smaller sizes, the 4000 trends narrow/tall to midlin'. the airfoil pro is long/low in its smaller sizes.
2. this is a lead-in to the next class, so, get ready: it's not the BIKE that determines the ratio. it's the BIKE + AEROBAR that determines the ratio. for example, if you take a p2 and put a 3T aura on that bike, and if you take a slice and you put a vision clip atop that bike, and you do this in the sizes listed above with the 42cm reach, you now have two bikes that are almost exactly the same height to length (assuming the stem length and pitch is the same on each bike).
so, don't get too hinky about the FRAME, rather, consider the entire construct aboard which you'll sit.
one more thing: what's the most mainstream bike on that list? trek speed concept. in every size, it's right smack dab in the middle. why? because trek plotted every bike in the market, and designed its geometry with the prime inputs as stack and reach. trek made a wager, that if its bike sat in the middle of the pack geometrically, it would fit as many customers as possible, and it would inoculate itself against any charge that its bikes were geometrically problematic. it wagered that if it simply erased that as a concern for as many people as possible, then it could concentrate on its narrative of superior aerodynamics.
that established, it's now up to bontrager to make aero bars that allow the entire construct to fit as many people as possible. in other words, bontrager has to do what trek did: make a geometrically mainstream bar; or it needs to make two bars: one high profile and one low; or it needs to make one bar that can be adjusted high or low profile. did bontrager do this? this spring we'll be reviewing aerobars and you'll find out. but in the next class, i'll equip you so that you can determine this yourself.
Dan Empfield
aka Slowman
it's not hard to divine. in very rough terms, if the stack of a bike is more than a third again its reach, it's starting to trend narrow/tall. so:
reach of 36cm x 1.33 = stack of 47.9cm
reach of 38cm x 1.33 = stack of 50.5cm
reach of 40cm x 1.33 = stack of 53.2cm
reach of 42cm x 1.33 = stack of 55.8cm
reach of 44cm x 1.33 = stack of 58.5cm
so, while a ratio of 1.33 or greater means it's trending narrow/tall, i think a ratio of 1.22 or smaller means it's trending long/low.
reach of 36cm x 1.22 = stack of 43.9cm
reach of 38cm x 1.22 = stack of 46.4cm
reach of 40cm x 1.22 = stack of 48.8cm
reach of 42cm x 1.22 = stack of 51.2cm
reach of 44cm x 1.22 = stack of 53.7cm
again, very general numbers. so, you take a bike that's got a reach of 42.0cm, if it's got a stack between 51.2 and 55.8 its a relatively mainstream bike, geometrically, at least as regards fit. let's see how some of these line up. here are bikes with a roughly 42cm reach, with their stack numbers, in order of long/low to narrow/tall:
kestrel airfoil pro size 52 reach 41.5cm stack 48.4cm ---- ratio: 1.17
kuota kueen k size 54 reach 50.3cm stack 42.6cm ---- ratio: 1.18
cervelo p3 size 54 reach 41.9cm stack 49.8cm ---- ratio: 1.19
cervelo p2 size 54 reach 41.8cm stack 51.2cm ---- ratio: 1.22
felt size 56cm reach 42.5cm stack 52.5cm ---- ratio: 1.23
orbea ordu size 57 reach 42.2cm stack 53.0cm ---- ratio: 1.23
argon18 E114 size M: reach 41.9cm stack 51.5cm ---- ratio: 1.23
qr cd0.1 size M reach 42.0cm stack 49.7cm ---- ratio: 1.26
trek speed concept size L reach 42.6 stack 54.1 ---- ratio: 1.27
specialized transition size XL reach 42.1cm stack 54.2cm ---- ratio: 1.29
cannondale slice size 58 reach 41.7cm stack 54.8cm ---- ratio: 1.31
scott plasma size L reach 41.6cm stack 54.8cm ---- ratio: 1.32
BH gc aero reach 42.0cm stack 56.0cm ---- ratio: 1.33
blue triad size ML: reach 41.4cm stack 55.8cm ---- ratio: 1.35
now, there are certain things to remember:
1. these bikes to not necessarily maintain these ratios throughout their size runs. for example, on our home page are write-ups of kestrel's 4000, and with its two tri bikes (the 4000 and the airfoil pro) plotted against trek's speed concept. the speed concept keeps to its ratio. the two kestrels do not. this is not a bad thing, it's just a notable thing, and it gives kestrel's retailers a pair of geometric styles to choose from when fitting their customers. just, neither model keeps to a single style. they're BOTH moderately trending long/low in their two largest sizes. but in their smaller sizes, the 4000 trends narrow/tall to midlin'. the airfoil pro is long/low in its smaller sizes.
2. this is a lead-in to the next class, so, get ready: it's not the BIKE that determines the ratio. it's the BIKE + AEROBAR that determines the ratio. for example, if you take a p2 and put a 3T aura on that bike, and if you take a slice and you put a vision clip atop that bike, and you do this in the sizes listed above with the 42cm reach, you now have two bikes that are almost exactly the same height to length (assuming the stem length and pitch is the same on each bike).
so, don't get too hinky about the FRAME, rather, consider the entire construct aboard which you'll sit.
one more thing: what's the most mainstream bike on that list? trek speed concept. in every size, it's right smack dab in the middle. why? because trek plotted every bike in the market, and designed its geometry with the prime inputs as stack and reach. trek made a wager, that if its bike sat in the middle of the pack geometrically, it would fit as many customers as possible, and it would inoculate itself against any charge that its bikes were geometrically problematic. it wagered that if it simply erased that as a concern for as many people as possible, then it could concentrate on its narrative of superior aerodynamics.
that established, it's now up to bontrager to make aero bars that allow the entire construct to fit as many people as possible. in other words, bontrager has to do what trek did: make a geometrically mainstream bar; or it needs to make two bars: one high profile and one low; or it needs to make one bar that can be adjusted high or low profile. did bontrager do this? this spring we'll be reviewing aerobars and you'll find out. but in the next class, i'll equip you so that you can determine this yourself.
Dan Empfield
aka Slowman