In the last twenty years the selection of available bicycle frame sizes, designs, and materials has changed dramatically.
Not only are there numerous bicycle styles to choose from (recreation, touring, road, mountain, etc.), but each person has a different body type, riding style, flexibility, and fitness level. And each of these determines your position on a bike.
When you buy a bicycle from Ben’s Cycle, we will make sure you get the correct size frame, and the purchase price always include a basic fit with our professional bike fitters.
But if you buy a bike somewhere else, you need to know what size frame you should be on. So we want to provide some very basic measurement tools that are by no means guaranteed for you since there are so many variables in your body measurements and the bike. A poor fit can lead to sore knees, backs, shoulders, and rear ends.
Our goal at Ben’s Cycle is to help more people ride their bikes more often, more safely, and more comfortably. So while a fit at a bike shop is best, here are some guidelines to get the correct bike frame and be comfortable on it.
You can reach Brett at firstname.lastname@example.org or at 414.384.2236.
Frame: Size Matters
The first step is to select the right size frame. In the past, you’ve probably stood over the top tube of a bike and checked how much stand over space you had by raising the bike into your crotch. If you had just the right amount, you were good. If you had too much or too little, you had the wrong size.
This method doesn’t really work. It doesn’t account for bikes with no top tube or with sloping top tubes, nor does it account for riders with different body shapes.
A good place to start is finding your inseam. Stand up against a wall. (It helps to have a partner help you with this.) Place a book between your legs as high as you can comfortably make it.
Measure the distance between the floor and the top of the book in centimeters. Brett Meinke, our professional bike fitter and human movement specialist, suggests using this formula as a basic rough measurement for an estimated frame size:
Bike Frame Size (cm) = Inseam (cm) x 0.67
Saddle Height: Just the Right Angle
Once you have the rough size for your frame, you need to put the saddle (seat) at the right height. Any time we talk about saddle height, we measure from the center of the bottom bracket (where the arms for the pedals come out) along a straight line of the seat tube of the bike frame to the middle of the saddle.
Use the measurement for your inseam again and multiply it by 0.883. (For example 86.4 x 0.883 = 76.29cm)
Measure from the center of the crank bolt as shown here along the seat tube to the top of the saddle.
Saddle Position: Fore and Aft
The third measurement we take when we do fits is to position the saddle. This is referred to as the fore and aft position of the saddle, moving it forward and back. The measurement is called the setback, as in how far back is the saddle from the bottom bracket.
The usual way to measure this is with a plumb bob, or a heavy washer attached to a string. When you are on the bike on a trainer, stop pedaling when the cranks arms are parallel to the ground. Hold one end of the plumb bob on your knee cap and allow the washer end to fall to just below the pedal.
The string should line up at the pedal axle. Adjust the saddle forward or back until the string is at the axle position.
When you’re finished, your right leg should have roughly this angle:
And when your crank is at 90 degrees, your knee and leg should look roughly like this:
And when your leg is at the top of the pedal stroke, it should look like this:
Stem Length: How Far Can You Reach
The final measure is how far you extend your upper body to reach the handlebars (called “reach”). This can be a challenging measurement since there is no real formula. Your reach depends on your arm length, physical condition, riding style, flexibility, and riding preferences. Men tend to have longer torsos and will often need a longer stem; women tend to have shorter torsos and therefore might need shorter stems.
Likewise, some might prefer a more upright riding style and want a stem that is short and up. Your weight should feel reasonably balanced between your rear end and your hands; your elbows should be bent so you can absorb more road shock and stay in better control.
Austin’s position on the bike is just right for in this photo. She wants to be a little more upright in her position, yet her upper body weight is roughly evenly distributed between her saddle and bars.
Bike Shop Fit
While these guidelines are just that: guidelines, they can get you positioned on a bike. But as you can tell, there is a lot of calculation and close observation that goes into a proper bike fit. These guidelines can get you close, but doing any of the measurements or calculations incorrectly can lead to discomfort on the bike.
Since we want you to enjoy your time on the bike and ride more, please make an appointment with a professional bike fitter at your local shop if you experience any of these symptoms because they usually indicate a poor bike fit:
- Shoulder pain
- Lower or upper back pain
- Neck pain
- Knee pain
- Wrist pain or numb fingers
- A sore, chafed, and bruised crotch or private parts
Standard frame measurement terms
Seat Tube: Measured from the center of the bottom bracket along the center to a point manufacturers depending on the frame design.
Top Tube: Measured from the frame size point horizontally to the steering tube axis.
Setback: (used as a more accurate way to measure seat tube angle) the horizontal distance from a vertical line passing through the bottom bracket to the frame size point.
Head Tube Length: The length of the head tube (not including headset components)
Seat Tube Angle: The angle of the line passing through the bottom bracket and frame size point relative to the horizontal.
Head Tube Angle: The angle of the steering axis relative to horizontal.
(These two angles affect the ride quality and do not directly affect the bike fit.)
We appreciate you taking the time to read through the Ben’s Cycle Guide to Finding the Right Size Bike Frame. We hope that is provides enough information to get you started to riding more and more comfortably!
Again, we highly recommend getting a bike fit from a qualified and trained technician.
Our bike fit expert, Brett Meinke, has worked at Ben’s Cycle for nearly 10 years doing fits. Brett, who has a degree in exercise physiology, has received specialized training in building orthotics, bike fits, and he has managed and coached several professional cycling teams.
You can reach Brett at email@example.com or at 414.384.2236.