Time Trial/Triathlon Bike Fit
"Cycling is a marriage between the cyclist, who is somewhat adaptable, and the bicycle, which is somewhat adjustable." - Andy Pruitt
Over the last several years, I have had the opportunity to work with serious athletes, including some national and even world champions, on their bike fit and equipment choices. This is an attempt to boil down that knowledge so that you may have a better understanding of how to make your position more powerful and aerodynamic.
Basically, there are two areas to look at in bike fit. One is saddle position and the other is handlebar position. Saddle position is the key to pedaling mechanics and is based on a few hard, scientific measurements. Handlebar position, which determines aerodynamics and comfort, is subject to more interpretation.
FOOT POSITION: Your cleats should be adjusted so that the ball of your foot is directly over the pedal axle. To avoid joint pain and possible future injury, your cleats should also be adjusted so that your foot rests on the pedal naturally. This means that whatever your feet do (point in, point out, left out, right straight, etc.) when you are standing straight up and relaxed, is what your feet should look like on the pedals at the bottom of the pedal stroke.
SADDLE HEIGHT: There are many different methods of determining saddle height, but all the good ones basically end up with the same thing. With your foot at the bottom of the pedaling stroke, in the correct pedal position, the angle from your thigh to calf should be approximately 25-30 degrees.
SADDLE FORE AND AFT: Triathlon bikes have steep seat tube angles for two reasons: The first and the most commonly mentioned, is that having your saddle in a forward position helps aid the transition from ride to run. The second reason, and I feel on that is often overlooked has to do with hip flexion.
Basically, with your legs properly extended, there should be an approximate 90 degree angle between your thighs and lower back measured through your hip joints. As you drop your handle bars in an effort to get more aerodynamic, this angle becomes acute. Therefore, in order to open up this angle, the rider must be rotated in an arc forwards of the bottom bracket. Put simply, as you get lower, you must also go forwards and a little up.
HOW TO SIT ON YOUR SADDLE: In order to help flatten your back and reach your handlebars with less strain on your back and shoulders, you should slide back on your saddle and then roll forward on the front part of your crotch. This should rotate your pelvis forward and down and take the hump out of your back. This may seem uncomfortable with your current saddle, but there are now many different saddles that may help to relieve pressure.
TOP TUBE/STEM LENGTH COMBINATIONS: Two general rules apply here. The first, the distance from the nose of your saddle to the stem should be 1-1.5 inches greater than the length of your forearm. The second is that distance from the center of your saddle (over the seat post) to your elbow pads should be equal, approximately 97% of your torso length (more for the very tall riders, less for the vertically impaired).
Having followed these measurements, when you are riding on your aero bars, your ears should be directly above your elbows.
HAND POSITION: Hand position is very important to lowering your frontal area and thereby decreasing drag. First, your forearms should be as close to each other as comfort allows. Then, when riding on your aero bars, the bottom of your hand should NEVER be below the inside of your elbow.
HEAD POSITION: Lowering your head as much as possible greatly decreases your frontal area and allows for smoother air flow over your back.
With your head up, your chest is open and catching all the wind. With your head down, you are more bullet-shaped.
Please remember to keep your head up enough to see down the road to safely navigate (don’t just stare at your front wheel).
KNEE POSITION: While pedaling, keep your knees as close to the top tube as possible. If your feet naturally pronate, your knees can probably brush the top tube on their way by. If your feet supinate, it will be very difficult for you to keep your knees in.