I’m going to assume that you have already purchased a bike to suite your needs, if not then a reputable bike shop will be able to guide you in making the correct purchase. As a crank is expensive, this is also an important consideration when purchasing your bike. The most common lengths available are 160, 165, 170, 172.5, 175 and 177.5mm. This has nothing to do with the gear ratio, but rather the actual length of the crank arms.
As a general rule of thumb you can use the following as a guide line:
Inseam to 78.74cm = 170mm cranks
Inseam 78.74 to 83.82cm = 172.5mm cranks
Inseam 83.82 and above = 175mm cranks
A good starting point in any bike setup is your cleat position, however, this is quite specialized and to obtain the correct cleat position ideally an “arch-o-meter” would be required. However as a rule of thumb, when clipped in, ensure that the axle of the pedal is directly under the ball of your foot and your feet are parallel to one another.
The next point of contact with the bike is your saddle. As there are literally thousands of variations on the market my advice here is find one that fits YOUR anatomy. Don’t go for what’s cool, or what’s light, go for what’s comfortable for you. Again you will need the help of a reputable bike shop that has “demo” saddles for you to try as they are costly. Usually a shorter wider saddle will be more suitable for a lady however there are many theories with regards to this.
Most riders find it best to have the saddle parallel to the ground, however some saddles have a high back so in these cases instead of putting the level straight across the entire length of the saddle, use only the sitting portion of the saddle.
Saddle height is probably the most important measurement when doing a bike setup but generally a knee bend of around 30 degrees should suffice. A saddle too low can be associated with pain in the front or sides of the knee while a saddle too high can be associated with pain in the back of the knee, hamstring or Achilles. Knee angles are measured when the leg is at the bottom of the pedal stroke and the foot is in its usual pedal position.
Once you are satisfied with your saddle height, you need to set your saddle fore-aft position. Sitting on your bike in a comfortable position rotate your right leg to a 3 o-clock position. Drop a plumb line from the bottom of your knee cap and it should pass through the center of the pedal axle. There can be quite a bit of variance here as climbers like to have the plumb line about 1 – 2cm behind the axle while sprinters, time trialists and triathletes sometimes come forward of the pedal axle. After you have adjusted your saddle fore-aft position recheck your saddle height as this may have changed with the fore-aft adjustment.
Right, feet done, bum done, next contact point will be your hands. Once again there are many configurations available, depending whether it’s a mountain bike, road bike or triathlon bike. For the purpose of this article I will stick to a simple road bike setup and here you need to ensure that your handle bar width is pretty much that of your shoulders from acromion to acromion.
Now check to see the shifter are level and the easiest way to do this is to place a straightedge under the drops then line the bottom of each shifter (brake lever) up with this. Check your handlebar angle by running an imaginary line from the ends of your handlebar drops parallel to the ground.
In general, the higher your stem, the more power you can produce, and the lower your stem the more aerodynamic you will be. Aerodynamics may more than compensate for your power loss but you will need to find a compromise between comfort, power and aerodynamics.
Stem length and height will combine to determine your torso angle which can vary from around 45 degrees (recreational) to around 10 degrees (time trialists).
Two traditional methods used to determine stem length require the rider so sit on the bike with hands in the drops and elbows bent comfortably as if riding. Without moving your head look at the front hub, it should be obscured by the top of the handlebar. There should also be around 1cm clearance between the elbow and the knee. Recreational riders would be more comfortable with a slightly shorter and higher stem.
This should give you a very general “fit window” from which you can progress as an athlete. However, I once again stress, the best advice I can give you is to get a professional BikeFit that will suite your needs.
Until next time, keep the rubber side down...