Buy the Right Size Road Bike - Document Your Current Bike
https://vimeo.com/251040710/10d5e6dc4a
See below for a quick video on how to look up the geometry of older bikes.
[S3FILE file='newbike/PDF handout bike sizing.pdf'] Documentation Sheet
We only need to look at a few measurements, all of which are readily available to us by various means. We’re going to take these measurements not so that we can just replicate them with the new bike. If we were to do that then we’d be resigned to having all the same problems as the old bike.We’re going to use the dimensions from your current bike as our starting point. The better your current bike fits, the less work we’ll have to do in our modification process. The more issues you have, however, the more careful and deliberate we’re going to have to be when making this new purchase.
The main measurements/dimensions that we need to gather from your current bike are:
Effective Top Tube (ETT)
Head Tube Length (HT) and/or
StackReach
In truth, we don’t have to use all four of these measurements, but since there’s a good chance we will be able to access all of them, I feel they’re good to use.So what are these measurements and what do they mean?
Effective Top Tube: the horizontal measurement from the center of the seat tube to the center-top point of the head tube
Head Tube: a simple linear measurement of the actual head tube length from the where it meets the top and bottom cup of the headset
Stack: the vertical distance between the center of the bottom bracket and the center-top of the head tube
Reach: the horizontal distance between the center of the bottom bracket and the center-top of the head tube
Effective top tube/head tube lengths and stack/reach are paired together so that each pair is attempting to describe or make clear the same thing. The reason we chose these measurements is that they will tell us the most about the two metrics we’re most concerned with in regards to how a bike will fit: Effective Top Tube or Reach -- How far away or close will the handlebars be? Head Tube Length or Stack -- How high or low a position will the handlebars be in? These measurements alone won’t determine the bar height or the total length of the cockpit (from the saddle to the bars), but they are the elements of the frame that are most critical to get right at the beginning to attain the best bike fit possible because they affect the outcome of the cockpit length and bar height the most -- plus they’re fixed dimensions and not adjustable.
So once you purchase the bike, you’re stuck with whatever range in bar height or cockpit length this frame’s effective top tube/head tube allow. Get it wrong and you have a bike that may never be comfortable, powerful or efficient.
There is a false idea out there that Stack and Reach are superior as measurements to Effective Top Tube and Head Tube lengths. Stack and Reach are the newer kid on the block -- they’ve just recently begun making it into geometry charts. Each pair of measurements has its shortcomings and blind spots, and I don’t find one to be drastically better. I can definitively conclude that stack/reach aren’t superior -- they just have slightly different blind spots.
For example:Effective top tube measurement between two bikes may not be “apples to apples” comparisons because of differences in head and seat angles of the bike, but likewise a Reach measurement may be misleading because it only provides a horizontal measurement from the bottom bracket forward, and again fails to consider differences created by a slacker or steeper seat angle.
You will find each measurement to be imperfect but as long as you’re aware of the shortcomings of each and consider other measurements in your decision making you can still use them effectively to make an informed decision
.One distinct advantage I give to effective top tube/head tube is that they are relatively easy to measure accurately by hand in real life whereas stack and reach requires special tools in order to get accurate readings. Of course most of the time we’re going to be looking up the measurements in geometry charts but it never hurts to be able to break out the tape measure on the spot and get some numbers.
So how do we find these frame metrics?
It's actually pretty easy these days. Every manufacturer lists them on their website. They're pretty easy to track down -- usually after navigating to the make and model in question it'll be somewhere on that page. Occasionally Effective Top Tube will be listed as "Horizontal Top Tube" or something similar
How to find effective top tube, head, stack, and reach for an older bike:
https://vimeo.com/384273224/ccdab9c259
Beyond ETT/HT and Stack/Reach there are just a few other simple dimensions to take from your current bike. These measurements will provide further information regarding the two main fit characteristics of the bike -- namely how far away or close the bars are from the seat and how high we can get the bars. What sets these apart from the measurements we’ve looked at so far is that these measurements are flexible and in most cases we can make changes to them in order to impact the fit of the bike:
Saddle fore/aft position -- We can slide the saddle forward and back on the seatpost rails which will change the distance between the saddle and the handlebars. We’ll learn shortly that in most cases we shouldn’t move the saddle to change the length of the bike’s cockpit because the saddle fore/aft position should be set beforehand to get the hips the proper distance behind the feet and this distance then shouldn’t change when the cockpit length is addressed. Regardless of this semantic issue saddle fore/aft still impacts the cockpit length of the bike.
Number of headset spacers -- Most modern bikes have a limit of 35-40mm of spacers under the stem allowed and they function to raise or lower the bar height. Now while it’s true that once a bike’s steerer tube is cut we can’t add any more spacers so we lose this ability to raise the bar, we may consider one bike over another because it might have more flexibility in bar height due to the fact that more spacers were left in place. Unfortunately many bike shops pre-cut their bikes to less than the allowable number of spacers -- perhaps 25-30 mm-- out of simply laziness which can perhaps make or break the bike for a given client fitting it. The way these steerers are built, they could easily be left at the maximum allowable height (to accommodate 35-40mm of spacers) while on the floor and then if the bike were sold to a client that didn’t need all of them and wanted the excess removed for aesthetic purposes, the steerer can be re-cut.
Stem length and rise -- The stem does double duty as it can affect the cockpit length AND the bar height. It’s not too hard to grasp that the length will affect the cockpit length and the rise will affect the bar height. One aspect of the stem that needs to be addressed is that as the rise increases the length of the stem decreases. This is because stem lengths are measured not by how much they project forward, but along the length of its body. So a 90mm stem with 20 degrees of rise only projects horizontally forward 72mm. Assuming a 73 degree head angle, only -17 degree stems project forward the length that they’re advertised as. Generally we don’t need to do any trigonometry however since we can make our changes and decision making later on simply by comparing the dimensions on your current bike, including the stem, with what will create the best possible fit.
Seatpost Setback or Offset -- This is a metric that may have a small effect but we nonetheless need to track it. Seatposts on road bikes usually have their clamp that holds the saddle, offset to the rear of the bike. Usually the offset is between 15-25mm but they make seatposts with setback from 0-35mm. One example that’s come up more than once was when a client is trying to shorten the reach of their bike and they have a zero offset seatpost as well as having the saddle slid all the way forward on the rails. On the new bike, we may want to plan for a shorter effective top tube so that the saddle can be held closer to the center of the rails and perhaps with a setback seatpost which increases the likelihood that the rider will have improved hip position (relative to the feet) on the new bike.
Now What?
Now that we’ve documented your position we need to consider the next step. This will depend on how you feel on the bike (more on this later too) and what, if any, interventions have you taken so far -- have you changed your position and set-up on the bike already or is it pretty much the way it was on the floor of the bike shop? Of course, I don’t mean something as basic as changing the seat height, but rather have you tried a different stem length/rise? Changed saddles? Had a basic (or even advanced) where the saddle fore/aft, bar and cleat positions were assessed and perhaps altered?You should fall into one of these categories:
A -Bike Feel Great, no or few changes made
B -Bike feels great, changes made
C -bike doesn’t feel great, no or few changes made
D - Bike doen’t feel great, changes made
If your bike feels great (or even pretty darn good) and you have or haven’t made any changes (Groups A or B), then you don’t have too much to worry about -- you can proceed through the rest of this program in sequence.
If you have, like in Group D, issues on the bike, but you feel like you’ve tried a good number adjustments and changes (perhaps they’ve helped some?) then there’s a good chance that you too can proceed through. The changes you’ve made, and their relative effects -- even when small -- can give us enough information to draw conclusions for the new bike.
However, if you’re in group C, your bike doesn’t feel great (or even good) and you haven’t made significant alterations or examined your bike fit very closely, you may have more work to do in order to move smoothly through this program and get the outcome you’re looking for (i.e. a great fitting new bike).
Because we’re going to be drawing conclusions from your old bike, we want to make sure that the old bike tells us something worthwhile. If you might be leaving some bike fit changes on the table, then we’re not getting the full picture from it.For example, let’s assume you have saddle discomfort. If you haven’t trialed new postures or fit on the bike through some changes, you might miss out on the fact that changing your stem to 15* rise, or moving the saddle back on the seatpost a centimeter might partially or completely solve this problem. Of course, there’s no guarantee of this outcome, but if it hasn’t been looked at or tried…These tests or trials will do a couple things for you:
They might make your bike feel pretty good or at least better than it was. Yay! This would be a net win. And you’d move into Group B...able to proceed through the program. And,
It would provide you with more information to draw conclusions about the sizing of the new bike that we’ll be addressing in the next few sections.
So after simply documenting your current position, we need to make sure that you’re in Groups A, B, or D in order to proceed. And if you’re in one of those groups, but you’re still worried that you’re leaving bike fit changes on the table, don’t worry, when we start drawing conclusions from your current set-up (Section 4) you’ll be able to see if this is the case.