Bike Fit Basics

Jan 27, 2021

You may think that all bikes are the same.  In many ways this is correct.  But, bikes consist of a frame, components, saddle, handlebars/aerobars, gearing, brakes, wheels, and accessories.  The bike frame consists of different materials with different weight, aerodynamics, fueling options, and responsiveness.  Finding the right bike is like picking out a pair of running shoes.  There are so many options to choose from, it is hard to know what to buy.  With shoes, you can buy several pair and often return them if they do not work.  Buying a bike is a commitment and large investment.

Bike Size:

When considering a bike, be sure to purchase a size that works for you.  Bikes are measured based on the height of the top tube measured in centimeters.  Have someone measure from the floor to your crotch while you are barefoot.

For a bike with a level top tube (the bar from the handlebar stem to the seat post), you should have one to two centimeters of space to your crotch when standing over the bike with both feet flat on the ground.  For bikes with a sloped top tube, allow a couple of inches.

Aero Bars:

If you are a triathlete, you can choose a time trial bike which increases aerodynamics by shifting your body forward and lower with aero bars.  If you already have a road bike or need to stay on a budget, you can add aero bars to a road bike.


Bike Fit:

Before you purchase your bike, discuss options for an initial bike fit.  Any quality bike shop will offer to do a minimal fit assessment to get you out the door safely.  If your first few rides are comfortable, continue riding for a few weeks and then schedule a time for a more comprehensive bike fit.  These sessions can last a couple of hours.  Research to find the best professional bike fitter in your area.

Having the right fit keeps pressure on the pedals, increases speed, and reduces overuse injuries.  There are many adjustments the bike fitter will consider.  Here are the main ones:

  • Cleat position
  • Saddle height
  • Saddle position
  • Aero bar length
  • Aero bar height

The key is to balance comfort, aerodynamics, and power output.  Comfort should come first.  What position can you sustain comfortably on a long ride?  If you must sit up often because you are uncomfortable, then you lose all the benefits of your aerodynamic setup.

If you do not notice a difference, go with a lower more aero fit.  Practice with it to make sure you can sustain it.  If you have a power meter, monitor your power output to see if it is consistent, improves, or decreases.  A small drop in power may be acceptable if you are comfortable and the aerodynamic gains are great.

Comfort starts with your saddle.  Sometimes it is necessary to replace the saddle to get a comfortable ride.  You may not know if discomfort is because of the type of saddle or how the bike fits your body.  When you first start riding, rear end discomfort is common.  Invest in quality cycling clothing and consider creams to reduce the friction between your legs and the saddle.

Before making any adjustments to your bike, document the current positioning of the saddle and the aero bars.  Then you can always revert if a change does not improve your setup.


Cleat position:

While wearing your cycling shoes, find the widest part of the foot in the shoe and mark the shoe with a marker or a piece of tape.  Then align the middle of the cleat with your marking or slightly behind your marking.  This will ensure that the force from your legs is driving through the foot into each pedal stroke. 

Saddle Height:

You need proper knee flex and leg extension to get the full benefit of each pedal stroke.  To find the right height for the saddle, the bike fitter will have you sit on your bike in aero position with the crank arms aligned with the seat post.  Your feet should be in the same position as if pedaling.  Often this is level with the ground.  It may be best to spin for a few minutes to warmup.  The angle from your hamstring, through the back of the knee, into the calf should be between 140 to 150 degrees.  Adjust the saddle height up or down to get the proper leg extension.  If your saddle is too low, you may bounce while pedaling.  If your saddle is too high, you may rock back and forth or end up pointing your toes on each stroke.  Having the right leg extension helps maximize usage of the glutes and quads.

Saddle Position:

Next the fitter will likely look at the distance the nose of the saddle is behind the bottom bracket.  To find the right position (setback), the fitter will have you align your pedals with the ground.  Then a plumb line will be dropped from the tip of your front kneecap to see if it aligns with the front of the crankarm.  If not, the saddle can be moved forwards or backwards to correct the positioning.  This helps ensure your power is going into propelling the bike forward through the pedals.  If the saddle position is adjusted, the saddle height should be revalidated.

In the aero position, the plumb line may show that the knee is slightly ahead of the crank arm.  This may be fine if you have an aggressive low forward aero position.

Aero Bar Length:

The bike fitter will have you lean into your aero bars and ride for a few minutes.  The fitter will look at the angle from your torso, through the shoulders/arm pits into the upper arm ending at the elbow on the aero pads.  The key is to take pressure off the back by moving the aero bars forward or backward until your upper arm is perpendicular to your torso.  This is not 90 degrees in relation to the ground.  Instead it is in relation to your back/torso.  Having the right angle should be comfortable.  If you are too far forward or backward, you create stress that will lead to discomfort and decreased performance.

The aero pads should be positioned so your arms hang inside your shoulders creating a slightly narrower grip on the aero bars.  But beware that the narrower your grip, the less control you will have on the road.  Error on the side of caution and do not be too aggressive on getting narrow.

When positioned correctly, you should be able to ride with very relaxed hands with your weight resting on your saddle and aero pads.

Aero Bar Height:

As mentioned before, comfort and safety are the top priorities.  In theory, if you can lower the aero bars so that your head, shoulders, and back are straight in alignment to your hips, you will punch the smallest hole through the wind as you are riding.  But this low position may not be possible based on your size, fitness, flexibility, age, cycling skills, etc.  As adjustments are made, ride on the trainer for a few minutes to gauge comfort and power output.  Continue to adjust until it gets worse or you are within 5 degrees of being level.  If the last adjustment was too much, the fitter will revert to the last good position and maybe slightly higher to be safe.

The bike fitter may also angle the aero bars up slightly.  Again, this creates a narrower grip decreasing the size of the hole that you create when cutting through the wind.


This was my setup for the Ironman World Championship.  Based on my size, flexibility, etc.  This was the best combination of comfort, power, and aerodynamics for me.


After adjusting all of these, it is a good idea to revisit each setting again to see how they work together. 

There are a lot of ways to gain speed on the bike.  The best place to start is with a bike fit.  After this, you can start customizing your setup based on what your budget allows.  Some of the key investments for improving performance include the helmet, wheels, and tires.  But aerodynamics is exponentially related to the speed you ride your bike.  The faster you go, the more wind resistance that must be overcome.  The result is that faster riders will see greater gains by investing in aerodynamic gear.  Slower riders will see some benefits.  But since they ride against less wind resistance, aerodynamic gear provides less value.

Invest in a Professional Bike Fit

We have covered some of the basics of bike fitting.  There is a lot more to it than what we have covered here.  But this gives you an idea.  It is worth the investment to work with a professional bike fitter.  Some say that bike fitting is more art than science.  This may be the case since you cannot rely on simple mathematical formulas.  You must find what fits your unique capabilities.  Investing in a bike fit will help you be more comfortable, safer, perform better, and be more satisfied riding.


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