Every cyclist should have some of their key bike measurements recorded. Without this information it's going to be difficult to get your position dialed in should any of the following apply:
It's important to make sure that your measurements are repeatable and consistent, and it's usually best to use protocols that are widely recognized and accepted. I use Park Tool's Road Positioning Chart to record everything; they also have a great online tutorial which will demonstrate how each of the measurements should be taken. Here are the links where you can download both the PDFs, and view the tutorials:
The distance from the center of the bottom bracket to the bottom of a board or straight edge, placed across the length of the saddle (taken in line with the seat tube). Is this your actual saddle height? Probably not, because most saddles are not flat, so there will usually be a gap between the bottom of the board and the top of the saddle. The flatter your saddle, the closer this measurement will be to your actual saddle height. The more cupped your saddle, the farther this will be from your actual height. The purpose of this measurement isn't to necessarily capture your actual saddle height, but rather to establish a method that will allow you accurately record changes or transfer the same saddle height to another bike.
Saddle height over bars (saddle to handlebar drop)
Park Tool has two methods for recording this, and I prefer the one where you take two measurements and subtract the difference. First, record the distance from the floor to the bottom of a board or straight edge across the saddle's length (taken at the nose of the saddle). Next, record the distance from the floor to the tops of the handlebars. Subtract the second measurement from the first one, and you'll know how high your handlebars are over your saddle. Keep in mind that since the first measurement is taken at the nose of the saddle, any change in your saddle tilt will also change this measurement. If you raise the nose of your saddle, it will cause the saddle to handlebar distance to increase.
Saddle to handlebar distance (reach)
This is the distance from the nose of the saddle to center of the handlebars at the stem. All of the following can change this distance: saddle height, fore/aft position, adding or removing stem spacers, and/or stem changes (either a different length or different rise). This measurement is typically the benchmark for "reach to the handlebars."
Saddle to hood distance (reach to hoods)
Although not recorded on the Park Tool Chart, I also recommend taking this measurement. It is the distance from the nose of the saddle to the tip of the brake lever hoods. This distance will change for all the same reasons mentioned just above, but this distance can also change even if the saddle to handlebar distance remains the same. Why? If you change to handlebars with different reach dimensions, rotate your handlebars, and/or change to a component group with different hoods, your saddle to hood distance can change, yet the saddle to handlebar distance at the stem will remain the same.
Using a straight edge across the length of the saddle, record the angle from horizontal using an angle finder, or even better, a digital level. I also recommend recording the level of the saddle in the approximate area where your sit bones rest.
Saddle fore/aft (saddle setback)
Drop a plumb bob from the nose of the saddle and measure the distance from the center of the bottom bracket to the plumb line. This measurement can change if you change the tilt of your saddle, even though you may not have changed the fore/aft position of the saddle on the rails.
You'll notice one constant in every one these measurements - the saddle. Change your saddle and almost every measure can change, especially if the new saddle has a different length. Changing saddles can be one of the most significant changes you can make to your equipment and it can really take some time to get everything dialed in to the way you had everything before the change. My advice when you are getting a new bike is to use the same saddle you've been used to riding, otherwise its going to be a real chore trying to replicate your position from your old bike. Of course, if your current saddle is not comfortable, then by all means make the switch.
Lastly, many of my clients are cyclists who had recently purchased a bike, and then found they couldn't get things to feel quite right, or even ended up in pain and discomfort; they simply couldn't figure out what had changed. Carefully recording your position and keeping the same saddle (or a new one of the same make and model) goes a long way towards knowing exactly how a different bike may change your position.
Eric Bowen, the owner of VeloFitter, is the author of all articles.