FIT: The endless well source of heated discussions, opinion and disagreement. If you’ve arrived here by some chain of events, I think one thing every reader needs to understand is FIT does not need to be confusing or difficult. We can have heated discussions over the nuances of FIT, but the methodology to achieve a proper FIT for a bicycle is actually quite simple. We’ve been led to believe its complex, involves lasers or plumb bobs, or at worse is some sort of dark art with mysterious origins. (And for the record… if your fitter brings out either a laser or a plumb bob… RUN). I’ve been riding mountain bikes just shy of 40 years, 20+ of them I’ve been building custom bicycles. So let me state something that is tried and true: The most important take away is that no one number in isolation should be considered; rather its a series of measurements that lead to FIT, and that each of us are unique in what is important to optimize our own FIT. What works for myself for example may not work for this guy or that guy for that matter. However, there are a set of universal measurements we can all use to determine the sum total of FIT for ourselves first based on measurements taken from our person, second taken from our bike and third observing the relationships between the two sets of measurements to hone how we balance ourselves between two wheels. FIT, geometry and handling go hand-in-hand, but often what determines handling (geometry) can be conflated with FIT. That’s a tight rope we all walk. Understanding the relationship between these 3 can go a long way. Over the years, I’ve slowly honed the art of my personal approach to FIT. And as a framebuilder, I’d like to share this rather simple methodology with all of you to help de-mystify any confusion swirling around FIT. However, before we walk down that yellow brick road, lets first go over a glossary of terms.
Geometry : Glossary of Terms
Reach: The horizontal distance from the center top of the head tube to the bottom bracket center.
Stack: The vertical distance from the bottom bracket center to the top of head tube center.
Layback: Reach minus effective top tube. Or put another way: the horizontal distance from bottom bracket center to seat tube centerline at the vertical and horizontal terminus of reach and stack. (I’d advocate for this to accompany reach and stack – and its a term I’ve used to explain this important missing measurement).
Effective Top Tube Length: Horizontal distance measured between the top of the head tube’s centerline and seat tube centerline.
Cockpit: Center of the handlebar/stem connection measured horizontally to tip of saddle.
Nose: Horizontal distance from saddle tip to saddle rail / seat post clamp center.
Saddle Height: Distance measured along seat tube centerline from bottom bracket center to horizontal top of saddle. (Often there is a valley from tip to tail on a saddle so be sure to lay something flat across the saddle to achieve this measurement more accurately).
First things first: The discussion below about FIT is as it relates to a modern mountain bike. How I FIT bikes for customers applies to gravel bikes as well, but for the sake of this discussion, we’re strictly referencing mountain bikes. Before I get into my method of FIT, let’s first air some dirty laundry and start with the first 2 terms mentioned above: Reach and Stack. These are two tried and true measurements that the industry at large has rightfully hung their collective hats in an attempt to create a universal method of helping potential customers understand how their current bike may stack up to a new bike (pun intended…). However, there’s a CRITICAL measurement missing from this set of measurements: Its Reach MINUS Effective Top Tube. What’s this number called? I refer to it as LAYBACK. Stamp that into your memory banks: LAYBACK. Reach MINUS Effective Top Tube (RMETT for all those acronym types out there). This is the number everyone circles around and I think is a source of a lot of confusion when it comes to FIT.
Let me explain why I think this is: Modern progressive mountain bike geometry often has steeper than “normal” seat tube angles. If reach remains the same, but your steepen seat tube angle, you shorten Layback and remove length from Cockpit. So the bike that you *think shares the same Reach technically won’t share the same FIT. But what if you just go off of Effective Top Tube? More confusion ensues… What if the reach is the same but the effective top tube is longer due to a slacker seat tube angle which puts your butt further behind the bottom bracket and further back over the rear wheel? But what if you run different length stems on these two bikes that deliver identical cockpit lengths BUT because one has a slacker seat tube angle, your weight is further behind the bottom bracket, shifting your center of gravity and hence handling is noticeably different? On and on and on. This is why I propose showing LAYBACK as a metric in a geometry chart. This allows potential customers to look at and compare their current bike to a new bike with as much information laid plain. The more information you have the better informed you’ll be to make a decision on sizing up or down on a potential new frame. So that’s my argument for why Layback as a metric is important.
Now that we’re all on the same page, lets dive into my approach to “FIT and the Art of Geometry and Handling.” And… if you have not, start by reading my primer on “Geometry”.
First, I pull the following 5 measurements from a clients person. Here’s that list along with how you can measure them for yourself and follow along:
Inseam: In stocking feet, place a book spine facing up between your legs so that it comes in contact with your pubic bone. Stand in front of a wall or in a doorway up against a the door jam, and mark where the spine of the book comes in contact with the wall or / jam. This is your true inseam.
Arm Length: Make a “pistol” with your thumb and forefinger while your arm is outstretched parallel to the ground. Measure from where your collar bone meets the top of your shoulder to where the crotch of your thumb and forefinger meet. This is your arm length.
Torso Length: With the book still between your legs, measure to the top of your sternum which is about in-line with the centerline of your outstretched arm. This is your torso length.
Height: In stocking feet, stand straight and measure from the ground to the top of your head. This is your height.
Shoe Size: Your cycling shoe size in US or EU to check for toe overlap (gravel/road) or heal clearance (more so for mountain but useful for road/gravel as well).
The reason we start with your personal measurements is to establish a foundation of metrics. For example, for your height, is your inseam long or short? This can point to a long or short torso for your height which effect reach. This can have an effect on stem length too. Or a longer/shorter inseam can illustrate why you may have a long or short saddle height for your height. Which can impact bar to saddle drop, which calls atttention to weight distribution which effects handling. Is your arm length close to your torso length or significantly longer or shorter when compared to your torso? Arm length and torso length can dictate cockpit length and subsequently stem length, and weight distribution and again… handling. What we’re doing is simply recording data and then observing these numbers in isolation and comparing them to each other – some revelations on why your saddle height is so low or so high for example can be drawn from simply taking these measurements. But compromises in your bikes setup can ALSO be taken into account… so lets get these measurements!
Now here is the short list of measurements I take from a clients existing mountain bike. There’s only 7 measurements to triangulate a rider between the wheels. The first 4 being what I pull first in my own design process. Reach, Stack and Layback can be pulled directly from your bike or certainly can be pulled from the manufacturers provided geometry size chart.
Cockpit: Measure the horizontal distance from the center of your handlebars to the tip of the saddle.
Nose: Measure from the saddle tip to the connection between the rails and seatpost head.
Saddle Length: Measure the saddle from tip to tale horizontally.
Saddle Height: Measure from the center of the bottom bracket to the center TOP of your saddle.
Reach: Measure from the center top of the head tube centerline horizontally along effective top tube to where it bisects with the bottom brackets vertical centerline.
Stack: Measure vertically from the center of the bottom bracket to where this imaginary line bisects with the effective top tube.
Layback: Reach subtracted from effective top tube length.
Got those? Now then I take 3 additional peripheral measurements. Those are:
1. Stem Length and angle / degree of +/-rise.
2. Seat Post Type and type (straight or setback & what that setback is if known)
3. Saddle Type w/ length and width accounted.
Reach, Stack and Layback come last as references. In my design process, these do not drive the design of the bike but rather are a result of establishing cockpit, nose, saddle position and saddle height as those are primary metrics that establish that specific clients Reach, Stack and Layback. That is an important distinction. But those 3 measurements are instructive and useful metrics when looking at STOCK geometry which is what we’re directly addressing with regards to FIT.
Simply put: Reach, Stack and Layback establish a ballpark set of figures so any rider can understand if a bike they’re looking at purchasing can work for them. If these 3 numbers are close to or identical to their current bike, the purchase can be made more confidently and doing the work of finalizing their FIT by fine tuning cockpit, nose, and saddle height all the more easily. Why reference these 3 metrics next? Cockpit establishes your relationship to the bike at two contact points: Grips and saddle. Saddle height and nose determine proper leg extension but also fine tune your center of gravity (CG) and balance it between the two wheels. Stem length fine tunes cockpit and can adjust how upright or stretched out a riders preference may be. For example: Some riders prefer a more upright stance and run a shorter stem while others may want a more direct connection to steering characteristics and thus choose to run a shorter stem and compromise with a slightly more upright riding stance. Nose establishes fore/aft positioning of the saddle which determines your CG in relation to the bikes center. Bar width and rise also can fine tune rider position in space with relation to CG and the bikes center point further balancing the rider between the wheels. Crank length can lengthen or shorten saddle height which can alter CG. Those last set of measurements and metrics ultimate determine HOW your FIT is in relation to a given Reach, Stack and Layback and how your CG interacts with the bikes geometry all of which effect handling. Ultimately, geometry determines handling. FIT should compliment handling, not fight or negatively impact handling. Again, Reach Stack and Layback tell us if the bike will fit. Cockpit, Nose, and Saddle Height have the final say on our personal FIT to that bike. Handlebar width/rise/angle, stem length/angle, saddle length/position fore/aft, and crank length fine tune your personal FIT. And those components can allow a rider to make compromises in terms of what they prioritize. Maybe the rider primarily wants to prioritize seated climbing. Or perhaps give more emphasis on a bikes ability to descend. Any number of priorities can be considered and all of these metrics can be used to fine tune and tailor the ride to your personal preferences.
So now you’re probably wondering: “That’s all great. Now I’ve got these measurements… How the heck do I go about setting up my FIT for my bike?” This is the fun part and the part we’ve all been waiting for while I’ve been bloviating about terminology. You’ve got the right bike. Reach, Stack and Layback of your new bike are in your wheelhouse. Let’s start with your saddle height. First start with a level saddle (bike on level surface, straight edge tip to tale on your saddle and place a level on the straight edge: Find level). For saddle height, there’s a few ways to determine this. One is the Lemond Method where you take your inseam and multiply it by .883. That is a starting point of center of the BB to the center top of your saddle. Riding seated “JRA” your legs should have a slight bend to them as you pedal. Too much and you’re not high enough. Too little and your knee will have too much bend. Another method, which does not involve math, was handed down to me by none other than Ted Wojcik: Dropper post extended to max height while seated, place your heals of your riding shoes on your pedals (Flats or clips). Now backpedal. You should JUST be able to get the pedals around without rolling your hips or lifting your feet off the pedals IF you saddle height is at the correct height. Both of these methods aren’t an exact science (neither is FIT for that matter). Both require trial and error to find where your comfort level lies with leg extension.
Once you have saddle height set, lets move on to bar position. Viewing the bike from the side, I’ve found the *ideal location for your bars is ever dead even with your saddle height or approximately 1″ below your saddle height. This is personal preference but that’s where I’ve found it to be best. Adjust stack spacers accordingly if you have steerer enough to do so. Adjust roll of the bar – I like mine just ever so slightly rolled forward so the rise and grip area along the bar is about level with the ground. Bar width, start with the bars uncut. Over the course of several rides, move your grips in 1/4″ at a time without trimming them. I’ve found for my shoulder width and stature, uncut 780mm are perfect. This is a slow process but remember: You can always take material off.. but you can’t put it back on so only cut when you’ve determined that comfort zone.
Stem length: Typically bikes are designed around a specific length. I typically will design around a 50mm stem unless the client wants to optimize around a specific length. Note that the shorter the stem, the more direct contact you’ll have with steering characteristics but you’ll also shorten your cockpit measurement and be more upright. Again, this is a slow and steady process.
Stem chosen, set up your cockpit length. Typically veteran riders will have a set length from saddle tip to center of bars they prefer. Stem length and saddle position fore/aft determine this and you can tweak both to achieve that preferred length. I like to start with and design around a saddle centered on the rails. Some saddles have longer noses than others while some can be shorter with overall lengths being shorter. Take all of this into account, note previous saddle nose lengths and overall lengths and compare them with new saddle nose and overall lengths. So your cockpit from bike to bike with different saddles may differ by 1/4″. But if you do find a saddle you like.. buy two. Moving your saddle for and aft can assist with body positioning and CG location with relation to the bottom bracket. Again, this is all trial and error. But the point is to have a baseline setup.
Now go for a ride but make it seated pedaling only for this first stage. Observe “just riding along”. Are you comfortable? Do you feel cramped? Are you too stretched out? Or do you feel “just right”? Pay attention. Feel it out. Observe. Why JRA as a starting point? Its the most tangible way to observe your body positioning on the bike. Once you’ve got JRA dialed in, now take the bike out for an actual ride. Go after it. Hit every downhill, every climb, every sprint. Bunny hop the heck out of that stump. Slam that saddle and burn through turns. Repeat. But observe yourself as you ride. Do the bars feel too high? Is the saddle in the way at any point? Are you cramped or do you feel stretched out at some points? Hitting too many rocks with your pedals? (Maybe its time to try those 165mm cranks…). On and on and on. But observe and take note. From this initial ride, you can gather a lot of good intel. From that initial JRA spin around the block, you should be able to now fine tune bar positioning, saddle positioning, bar width, play with stem length and maybe even fiddle with crank length. This is a process of deliberate ride, observe, note, tweak, rinse and repeat. But that tweak? Only change one piece of the puzzle at a time. IF you change multiple points at the same time, you may make a change that wasn’t warranted and you’ll be wondering if it was your saddle height or your bar adjustment or… you get the point. Sometimes this all comes together on that first ride. Maybe it takes 2 or 3 rides. But its a slow and deliberate process of honing in on your personal FIT. But once you have things dialed, the bike will be an extension of you, FIT will compliment geometry and handling will fall into place and your fit won’t fight how the bike handles. Make sense?
And that’s FIT in a nutshell. FIT is only as complicated as we make it out to be. I strongly believe that having a key set of measurements and metrics close at hand makes the whole process all the more easy to achieve. However, its when we don’t have all of these metrics close at hand and a basic understanding of how they interact with one another, I think this is where the confusion begins. And for my own personal journey with bicycle FIT, it didn’t happen over night. It took a bunch of trial and error to hone in on my own personal FIT. Having these measurements and observing relationships removed the mystery and confusion. And once I had these measurements, boy it was so much easier to set up bikes where I immediately felt at home atop. I hope this helps solve some of the mystery behind fit and how to compare your current bike with a potential new bike!
Post Script: Here’s the full list of FIT and Geometry terms below. The above was an abbreviated short list just for our discussion of FIT.
Geometry : Expanded Glossary of Terms
Reach: The horizontal distance from the center top of the head tube to the bottom bracket center.
Stack: The vertical distance from the bottom bracket center to the top of head tube center.
Layback: The horizontal distance from bottom bracket center to seat tube centerline at the vertical and horizontal terminus of reach and stack. (I’d advocate for this to accompany reach and stack – and its a term I’ve used to explain this important missing measurement).
Head Tube Angle: The angle measured in degrees of the head tubes center line as it bisects a horizontal line defined as the axle centerlines.
Axle to Crown: Distance measured along the head tube centerline from crown race seat to front axle centerline. (Determine axle to crown and account for sag when designing a hardtail.)
Sag: Percentage of fork travel subtracted from axle to crown when fork is weighted by rider in a seated position.
Rake: This is the angle measured in degrees between the steering axis and a vertical line drawn from the front axle centerline. (In the past, this has been confused with offset in the bicycle world. Offset is offset. Rake is NOT offset.)
Offset: The distance measured perpendicularly from the steering axis to the centerline of the front wheel. (DO NOT REFER TO THIS AS RAKE)
Trail: The horizontal distance measured between where head tube centerline/steering axis and the perpendicular vertical distance of front axle centerline intersect with the ground. (More rake = more trail. Less rake = less trail. Simple, huh?)
Front Center: The distance from bottom bracket center to the front axle centerline (I’ve seen this measured as a pure horizontal distance and/or measured as the hypotenuse of the imaginary triangle formed by the bottom bracket and front axle with the axle centerline).
Cockpit: Center of the handlebar/stem connection measured horizontally to tip of saddle.
Nose: Horizontal distance from saddle tip to saddle rail / seat post clamp center.
Saddle Setback: Horizontal distance from seat post centerline to saddle rail / seat post clamp center.
Effective Top Tube Length: Horizontal distance measured between the top of the head tube’s centerline and seat tube centerline.
Actual Top Tube Length: Distance measured along top tube centerline where it intersects with seat tube centerline and head tube centerline.
Seat Tube Angle: Angle of seat tube centerline with horizontal centerline between front and rear axles.
Effective Seat Tube Angle: This is the measurement of the angle between BB center and Saddle Top (with curved or offset seat tubes, this centerline is often invisible).
Saddle Height: Distance measured along seat tube centerline from bottom bracket center to horizontal top of saddle. (Often there is a valley from tip to tail on a saddle so be sure to lay something flat across the saddle to achieve this measurement more accurately).
Bottom Bracket Drop: The vertical distance from the axle center line perpendicular to the center of the bottom bracket.
Bottom Bracket Height: The vertical distance from the bottom bracket center perpendicular to the ground.
Chainstay Length (or rear center): Horizontal measurement from bottom bracket center to rear axle centerline. (When measuring this distance for a singlespeed, its paramount to measure this as the hypotenuse to optimize chain length and dial in tension so the sliders stay as slammed as possible to allow for chain growth.)
Wheelbase: Horizontal measurement from front axle to rear axle centerlines.
RAD / Rider Area Distance: The 2D distance projected and measured between the bottom bracket and grips.
FIT
FIT: The endless well source of heated discussions, opinion and disagreement. If you’ve arrived here by some chain of events, I think one thing every reader needs to understand is FIT does not need to be confusing or difficult. We can have heated discussions over the nuances of FIT, but the methodology to achieve a proper FIT for a bicycle is actually quite simple. We’ve been led to believe its complex, involves lasers or plumb bobs, or at worse is some sort of dark art with mysterious origins. (And for the record… if your fitter brings out either a laser or a plumb bob… RUN). I’ve been riding mountain bikes just shy of 40 years, 20+ of them I’ve been building custom bicycles. So let me state something that is tried and true: The most important take away is that no one number in isolation should be considered; rather its a series of measurements that lead to FIT, and that each of us are unique in what is important to optimize our own FIT. What works for myself for example may not work for this guy or that guy for that matter. However, there are a set of universal measurements we can all use to determine the sum total of FIT for ourselves first based on measurements taken from our person, second taken from our bike and third observing the relationships between the two sets of measurements to hone how we balance ourselves between two wheels. FIT, geometry and handling go hand-in-hand, but often what determines handling (geometry) can be conflated with FIT. That’s a tight rope we all walk. Understanding the relationship between these 3 can go a long way. Over the years, I’ve slowly honed the art of my personal approach to FIT. And as a framebuilder, I’d like to share this rather simple methodology with all of you to help de-mystify any confusion swirling around FIT. However, before we walk down that yellow brick road, lets first go over a glossary of terms.
Geometry : Glossary of Terms
Reach: The horizontal distance from the center top of the head tube to the bottom bracket center.
Stack: The vertical distance from the bottom bracket center to the top of head tube center.
Layback: Reach minus effective top tube. Or put another way: the horizontal distance from bottom bracket center to seat tube centerline at the vertical and horizontal terminus of reach and stack. (I’d advocate for this to accompany reach and stack – and its a term I’ve used to explain this important missing measurement).
Effective Top Tube Length: Horizontal distance measured between the top of the head tube’s centerline and seat tube centerline.
Cockpit: Center of the handlebar/stem connection measured horizontally to tip of saddle.
Nose: Horizontal distance from saddle tip to saddle rail / seat post clamp center.
Saddle Height: Distance measured along seat tube centerline from bottom bracket center to horizontal top of saddle. (Often there is a valley from tip to tail on a saddle so be sure to lay something flat across the saddle to achieve this measurement more accurately).
First things first: The discussion below about FIT is as it relates to a modern mountain bike. How I FIT bikes for customers applies to gravel bikes as well, but for the sake of this discussion, we’re strictly referencing mountain bikes. Before I get into my method of FIT, let’s first air some dirty laundry and start with the first 2 terms mentioned above: Reach and Stack. These are two tried and true measurements that the industry at large has rightfully hung their collective hats in an attempt to create a universal method of helping potential customers understand how their current bike may stack up to a new bike (pun intended…). However, there’s a CRITICAL measurement missing from this set of measurements: Its Reach MINUS Effective Top Tube. What’s this number called? I refer to it as LAYBACK. Stamp that into your memory banks: LAYBACK. Reach MINUS Effective Top Tube (RMETT for all those acronym types out there). This is the number everyone circles around and I think is a source of a lot of confusion when it comes to FIT.
Let me explain why I think this is: Modern progressive mountain bike geometry often has steeper than “normal” seat tube angles. If reach remains the same, but your steepen seat tube angle, you shorten Layback and remove length from Cockpit. So the bike that you *think shares the same Reach technically won’t share the same FIT. But what if you just go off of Effective Top Tube? More confusion ensues… What if the reach is the same but the effective top tube is longer due to a slacker seat tube angle which puts your butt further behind the bottom bracket and further back over the rear wheel? But what if you run different length stems on these two bikes that deliver identical cockpit lengths BUT because one has a slacker seat tube angle, your weight is further behind the bottom bracket, shifting your center of gravity and hence handling is noticeably different? On and on and on. This is why I propose showing LAYBACK as a metric in a geometry chart. This allows potential customers to look at and compare their current bike to a new bike with as much information laid plain. The more information you have the better informed you’ll be to make a decision on sizing up or down on a potential new frame. So that’s my argument for why Layback as a metric is important.
Now that we’re all on the same page, lets dive into my approach to “FIT and the Art of Geometry and Handling.” And… if you have not, start by reading my primer on “Geometry”.
First, I pull the following 5 measurements from a clients person. Here’s that list along with how you can measure them for yourself and follow along:
Inseam: In stocking feet, place a book spine facing up between your legs so that it comes in contact with your pubic bone. Stand in front of a wall or in a doorway up against a the door jam, and mark where the spine of the book comes in contact with the wall or / jam. This is your true inseam.
Arm Length: Make a “pistol” with your thumb and forefinger while your arm is outstretched parallel to the ground. Measure from where your collar bone meets the top of your shoulder to where the crotch of your thumb and forefinger meet. This is your arm length.
Torso Length: With the book still between your legs, measure to the top of your sternum which is about in-line with the centerline of your outstretched arm. This is your torso length.
Height: In stocking feet, stand straight and measure from the ground to the top of your head. This is your height.
Shoe Size: Your cycling shoe size in US or EU to check for toe overlap (gravel/road) or heal clearance (more so for mountain but useful for road/gravel as well).
The reason we start with your personal measurements is to establish a foundation of metrics. For example, for your height, is your inseam long or short? This can point to a long or short torso for your height which effect reach. This can have an effect on stem length too. Or a longer/shorter inseam can illustrate why you may have a long or short saddle height for your height. Which can impact bar to saddle drop, which calls atttention to weight distribution which effects handling. Is your arm length close to your torso length or significantly longer or shorter when compared to your torso? Arm length and torso length can dictate cockpit length and subsequently stem length, and weight distribution and again… handling. What we’re doing is simply recording data and then observing these numbers in isolation and comparing them to each other – some revelations on why your saddle height is so low or so high for example can be drawn from simply taking these measurements. But compromises in your bikes setup can ALSO be taken into account… so lets get these measurements!
Now here is the short list of measurements I take from a clients existing mountain bike. There’s only 7 measurements to triangulate a rider between the wheels. The first 4 being what I pull first in my own design process. Reach, Stack and Layback can be pulled directly from your bike or certainly can be pulled from the manufacturers provided geometry size chart.
Cockpit: Measure the horizontal distance from the center of your handlebars to the tip of the saddle.
Nose: Measure from the saddle tip to the connection between the rails and seatpost head.
Saddle Length: Measure the saddle from tip to tale horizontally.
Saddle Height: Measure from the center of the bottom bracket to the center TOP of your saddle.
Reach: Measure from the center top of the head tube centerline horizontally along effective top tube to where it bisects with the bottom brackets vertical centerline.
Stack: Measure vertically from the center of the bottom bracket to where this imaginary line bisects with the effective top tube.
Layback: Reach subtracted from effective top tube length.
Got those? Now then I take 3 additional peripheral measurements. Those are:
1. Stem Length and angle / degree of +/-rise.
2. Seat Post Type and type (straight or setback & what that setback is if known)
3. Saddle Type w/ length and width accounted.
Reach, Stack and Layback come last as references. In my design process, these do not drive the design of the bike but rather are a result of establishing cockpit, nose, saddle position and saddle height as those are primary metrics that establish that specific clients Reach, Stack and Layback. That is an important distinction. But those 3 measurements are instructive and useful metrics when looking at STOCK geometry which is what we’re directly addressing with regards to FIT.
Simply put: Reach, Stack and Layback establish a ballpark set of figures so any rider can understand if a bike they’re looking at purchasing can work for them. If these 3 numbers are close to or identical to their current bike, the purchase can be made more confidently and doing the work of finalizing their FIT by fine tuning cockpit, nose, and saddle height all the more easily. Why reference these 3 metrics next? Cockpit establishes your relationship to the bike at two contact points: Grips and saddle. Saddle height and nose determine proper leg extension but also fine tune your center of gravity (CG) and balance it between the two wheels. Stem length fine tunes cockpit and can adjust how upright or stretched out a riders preference may be. For example: Some riders prefer a more upright stance and run a shorter stem while others may want a more direct connection to steering characteristics and thus choose to run a shorter stem and compromise with a slightly more upright riding stance. Nose establishes fore/aft positioning of the saddle which determines your CG in relation to the bikes center. Bar width and rise also can fine tune rider position in space with relation to CG and the bikes center point further balancing the rider between the wheels. Crank length can lengthen or shorten saddle height which can alter CG. Those last set of measurements and metrics ultimate determine HOW your FIT is in relation to a given Reach, Stack and Layback and how your CG interacts with the bikes geometry all of which effect handling. Ultimately, geometry determines handling. FIT should compliment handling, not fight or negatively impact handling. Again, Reach Stack and Layback tell us if the bike will fit. Cockpit, Nose, and Saddle Height have the final say on our personal FIT to that bike. Handlebar width/rise/angle, stem length/angle, saddle length/position fore/aft, and crank length fine tune your personal FIT. And those components can allow a rider to make compromises in terms of what they prioritize. Maybe the rider primarily wants to prioritize seated climbing. Or perhaps give more emphasis on a bikes ability to descend. Any number of priorities can be considered and all of these metrics can be used to fine tune and tailor the ride to your personal preferences.
So now you’re probably wondering: “That’s all great. Now I’ve got these measurements… How the heck do I go about setting up my FIT for my bike?” This is the fun part and the part we’ve all been waiting for while I’ve been bloviating about terminology. You’ve got the right bike. Reach, Stack and Layback of your new bike are in your wheelhouse. Let’s start with your saddle height. First start with a level saddle (bike on level surface, straight edge tip to tale on your saddle and place a level on the straight edge: Find level). For saddle height, there’s a few ways to determine this. One is the Lemond Method where you take your inseam and multiply it by .883. That is a starting point of center of the BB to the center top of your saddle. Riding seated “JRA” your legs should have a slight bend to them as you pedal. Too much and you’re not high enough. Too little and your knee will have too much bend. Another method, which does not involve math, was handed down to me by none other than Ted Wojcik: Dropper post extended to max height while seated, place your heals of your riding shoes on your pedals (Flats or clips). Now backpedal. You should JUST be able to get the pedals around without rolling your hips or lifting your feet off the pedals IF you saddle height is at the correct height. Both of these methods aren’t an exact science (neither is FIT for that matter). Both require trial and error to find where your comfort level lies with leg extension.
Once you have saddle height set, lets move on to bar position. Viewing the bike from the side, I’ve found the *ideal location for your bars is ever dead even with your saddle height or approximately 1″ below your saddle height. This is personal preference but that’s where I’ve found it to be best. Adjust stack spacers accordingly if you have steerer enough to do so. Adjust roll of the bar – I like mine just ever so slightly rolled forward so the rise and grip area along the bar is about level with the ground. Bar width, start with the bars uncut. Over the course of several rides, move your grips in 1/4″ at a time without trimming them. I’ve found for my shoulder width and stature, uncut 780mm are perfect. This is a slow process but remember: You can always take material off.. but you can’t put it back on so only cut when you’ve determined that comfort zone.
Stem length: Typically bikes are designed around a specific length. I typically will design around a 50mm stem unless the client wants to optimize around a specific length. Note that the shorter the stem, the more direct contact you’ll have with steering characteristics but you’ll also shorten your cockpit measurement and be more upright. Again, this is a slow and steady process.
Stem chosen, set up your cockpit length. Typically veteran riders will have a set length from saddle tip to center of bars they prefer. Stem length and saddle position fore/aft determine this and you can tweak both to achieve that preferred length. I like to start with and design around a saddle centered on the rails. Some saddles have longer noses than others while some can be shorter with overall lengths being shorter. Take all of this into account, note previous saddle nose lengths and overall lengths and compare them with new saddle nose and overall lengths. So your cockpit from bike to bike with different saddles may differ by 1/4″. But if you do find a saddle you like.. buy two. Moving your saddle for and aft can assist with body positioning and CG location with relation to the bottom bracket. Again, this is all trial and error. But the point is to have a baseline setup.
Now go for a ride but make it seated pedaling only for this first stage. Observe “just riding along”. Are you comfortable? Do you feel cramped? Are you too stretched out? Or do you feel “just right”? Pay attention. Feel it out. Observe. Why JRA as a starting point? Its the most tangible way to observe your body positioning on the bike. Once you’ve got JRA dialed in, now take the bike out for an actual ride. Go after it. Hit every downhill, every climb, every sprint. Bunny hop the heck out of that stump. Slam that saddle and burn through turns. Repeat. But observe yourself as you ride. Do the bars feel too high? Is the saddle in the way at any point? Are you cramped or do you feel stretched out at some points? Hitting too many rocks with your pedals? (Maybe its time to try those 165mm cranks…). On and on and on. But observe and take note. From this initial ride, you can gather a lot of good intel. From that initial JRA spin around the block, you should be able to now fine tune bar positioning, saddle positioning, bar width, play with stem length and maybe even fiddle with crank length. This is a process of deliberate ride, observe, note, tweak, rinse and repeat. But that tweak? Only change one piece of the puzzle at a time. IF you change multiple points at the same time, you may make a change that wasn’t warranted and you’ll be wondering if it was your saddle height or your bar adjustment or… you get the point. Sometimes this all comes together on that first ride. Maybe it takes 2 or 3 rides. But its a slow and deliberate process of honing in on your personal FIT. But once you have things dialed, the bike will be an extension of you, FIT will compliment geometry and handling will fall into place and your fit won’t fight how the bike handles. Make sense?
And that’s FIT in a nutshell. FIT is only as complicated as we make it out to be. I strongly believe that having a key set of measurements and metrics close at hand makes the whole process all the more easy to achieve. However, its when we don’t have all of these metrics close at hand and a basic understanding of how they interact with one another, I think this is where the confusion begins. And for my own personal journey with bicycle FIT, it didn’t happen over night. It took a bunch of trial and error to hone in on my own personal FIT. Having these measurements and observing relationships removed the mystery and confusion. And once I had these measurements, boy it was so much easier to set up bikes where I immediately felt at home atop. I hope this helps solve some of the mystery behind fit and how to compare your current bike with a potential new bike!
Post Script: Here’s the full list of FIT and Geometry terms below. The above was an abbreviated short list just for our discussion of FIT.
Geometry : Expanded Glossary of Terms
Reach: The horizontal distance from the center top of the head tube to the bottom bracket center.
Stack: The vertical distance from the bottom bracket center to the top of head tube center.
Layback: The horizontal distance from bottom bracket center to seat tube centerline at the vertical and horizontal terminus of reach and stack. (I’d advocate for this to accompany reach and stack – and its a term I’ve used to explain this important missing measurement).
Head Tube Angle: The angle measured in degrees of the head tubes center line as it bisects a horizontal line defined as the axle centerlines.
Axle to Crown: Distance measured along the head tube centerline from crown race seat to front axle centerline. (Determine axle to crown and account for sag when designing a hardtail.)
Sag: Percentage of fork travel subtracted from axle to crown when fork is weighted by rider in a seated position.
Rake: This is the angle measured in degrees between the steering axis and a vertical line drawn from the front axle centerline. (In the past, this has been confused with offset in the bicycle world. Offset is offset. Rake is NOT offset.)
Offset: The distance measured perpendicularly from the steering axis to the centerline of the front wheel. (DO NOT REFER TO THIS AS RAKE)
Trail: The horizontal distance measured between where head tube centerline/steering axis and the perpendicular vertical distance of front axle centerline intersect with the ground. (More rake = more trail. Less rake = less trail. Simple, huh?)
Front Center: The distance from bottom bracket center to the front axle centerline (I’ve seen this measured as a pure horizontal distance and/or measured as the hypotenuse of the imaginary triangle formed by the bottom bracket and front axle with the axle centerline).
Cockpit: Center of the handlebar/stem connection measured horizontally to tip of saddle.
Nose: Horizontal distance from saddle tip to saddle rail / seat post clamp center.
Saddle Setback: Horizontal distance from seat post centerline to saddle rail / seat post clamp center.
Effective Top Tube Length: Horizontal distance measured between the top of the head tube’s centerline and seat tube centerline.
Actual Top Tube Length: Distance measured along top tube centerline where it intersects with seat tube centerline and head tube centerline.
Seat Tube Angle: Angle of seat tube centerline with horizontal centerline between front and rear axles.
Effective Seat Tube Angle: This is the measurement of the angle between BB center and Saddle Top (with curved or offset seat tubes, this centerline is often invisible).
Saddle Height: Distance measured along seat tube centerline from bottom bracket center to horizontal top of saddle. (Often there is a valley from tip to tail on a saddle so be sure to lay something flat across the saddle to achieve this measurement more accurately).
Bottom Bracket Drop: The vertical distance from the axle center line perpendicular to the center of the bottom bracket.
Bottom Bracket Height: The vertical distance from the bottom bracket center perpendicular to the ground.
Chainstay Length (or rear center): Horizontal measurement from bottom bracket center to rear axle centerline. (When measuring this distance for a singlespeed, its paramount to measure this as the hypotenuse to optimize chain length and dial in tension so the sliders stay as slammed as possible to allow for chain growth.)
Wheelbase: Horizontal measurement from front axle to rear axle centerlines.
RAD / Rider Area Distance: The 2D distance projected and measured between the bottom bracket and grips.