A simplified approach to ‘transfer’ your Bike Fit positioning and measurements from bike to bike.
After a professional Bike Fitting, we are often asked about transferring the fit, or specific measurements on to another bike.
However, if you were to look at some of these complex fit diagrams these days with tube angles, BB drop, fork rake, chain- and seat-stay lenghts, stack-and-reach, etc, it can be extremely overwhelming to figure out what you actually need in order to replicate, or at least understand, your curent positioning/fit on your bike.
Paralysis by analysis as they say..
In an effort to distill all this information for you, let’s just jump into it: In the grand scheme of things, you really just need 3 (maybe 4) simple measurements to get a good understanding of your positioning on the bike.
#1) Saddle Height (Fig A)
This one is the most important, and always the first one to check. If this one is significantly off compared to your other bike, it will influence the next 2 measurements big time. We are basically measuring the distance from the center of the bottom bracket (the center point of the crank) to the top, center of the saddle, as is Fig A. It is important to mention the we measure to the TOP surface of the saddle, as there is great variation in saddle padding, shape, and rail height. But, the top of the saddle measurement should remain consistent regardless of saddle you are riding. Write down that distance in cm, and is usually between 60 and 75+cm depending on your height.
Note: Also take a look at how long your cranks are between the bikes, as this will influence the saddle height measurement. For example, if you ride 175mm cranks (all cranks are stamped on them what length they are), but the bike you are transferring the saddle height to are 170mm cranks, 5mm shorter- then you would need to add 5mm to your measurement- with a 170 crank you would be reaching a tiny bit less at the bottom of the pedal stroke. (Vice versa, if you initially measured saddle height on a bike w 170mm cranks, and transferring to a bike w 175mms, you would need to subtract 5mm from that initial measurement- Make sense? )
#2) Saddle to Handlebar Reach (Fig B, C)
Once the saddle measurement is dialed in, the next thing you’ll want to measure is what we call reach (or ‘cockpit depth’)- i.e. the distance from your saddle to the ceneter of the bars. We simplify this measurement by measuring from the tip of the saddle straight ahead to where the center of the stem (the piece that holds your handlebars) attaches, OR also from tip of saddle, to the top of brake hoods, and each have their variations. Write down that number in cm.
Note: This measurement is influenced by a myriad of factors including saddle fore/aft, length of top tube, stem, rotation of bars, the handlebar itself, and brake hood equipment and positioning, so understand you can usually optimaize inequalities between bikes by adjustments alone. If you are unsure how to adjust your equipment, or are unsure about the contributing factors of the top-tube length of your frame, reach out to a bike mechanic- or better yet, a bike-centric PT office, ahem- to help you out. :-)
#3) Drop (Fig D, E)
In Bike Fitting, we refer to ‘drop’ as the the vertical height difference of your saddle vs handlebars. This number can be either positive (meaning the bars are higher that the saddle) or negative (were the bars are lower than your saddle height). Different bike styles and goals for riding are all contributing factors to the amount of drop a rider can comfortably tolerate.
Measure it: Using a large level placed on the saddle, level it (or have a partner hold this level) and then use your tape measure to measure the vertical distance from the edge of the level to the top of the bars. Write down in cm.
Alternative method: You can measure the distance from the top of the saddle straight down to the floor, and then measure the distance from the bars to the floor- then subtract those 2 numbers. Can be kinda tricky depending on the equipment that gets in the way, but don’t stress out. Record that number.
This measurement is of course tied to saddle height, the stem itself and if there is any angle up/down to it, and where the stem is positioned on the steerer tube. Lots of variables to play with here! Again, if you have questions, please reach out!
So there you have it, 3 simple measurements that will get you 98% close to the same positioning on your other bike, but do remember, frame sizing, frame materials, head and seat-tube angles, wheelbase, tires, and many other factors will influence how your bike rides, and the comfort (or lack thereof) you will experience while riding . .
Feel free to reach out if you have questions, comments or feedback!