In order to figure out what size bike do I need, first use the what kind of bike should I buy calculator.
In a previous post, How to Measure a Bike Frame – Terminology, we discussed the basics of how to measure a bike frame and the bike terminology used when describing bike frames. Now, let’s specifically walk through the steps and explain how to measure a road bike frame. If you are unsure of any bike terminology used or need to refresh your memory, you may want to review the post listed above. Okay, but first, let me ask,
How to Measure Road Bike Frame – Do I need to know this?
Why do I need to know this? Is this useful?
Understanding how a road bike frame is measured can be useful when replacing your old bike to ensure you get a similar size frame.
I personally could have benefited from this information when I bought a used road bike once that was listed as a 56cm. If I understood how to measure the bike frame size then I would have realized that it actually was a 60cm before I bought it, not after 
If you test rode a friend’s bike and they don’t know the size, you could use this to find out.
There are a variety of reasons this information could be useful. When we understand that the central piece of the bike, the part that everything else attaches to or works together with is the frame, then you realize the when you ask what size bike should i ride, you are really asking what size bike frame do i need. Getting the right sized frame is the key to a well fitting, comfortable bike, as well as a future of happy bike riding.
How to Measure Road Bike Frame – Information:
Road bike frame sizing is traditionally measured in centimeters (cm).
One inch is equal to 2.54 cm.
Depending on manufacturer, road bike frame size may be measured from the center of the bottom bracket to the center of the top tube at the point the top tube intersects the seat tube. This is known as center to center (C-C), or road bike frame size may be measured from the center of the bottom bracket to the top of the seat tube. This is known as center to top (C-T). Since Measuring a Road Bike Frame can be done either C-C or C-T, just complete both measurements at once so you have them for reference.
How to Measure Road Bike Frame – What you will need:
You will need:
Measuring Tape (If the measuring tape is standard (not metric), you will also need a calculator to convert to metric.)
How to Measure Road Bike Frame:
- Place the end of the measuring tape at the middle of the bottom bracket
- If cranks are installed: measure from the center of the bolt (or dustcover covering the bolt) that secures the crankarms to the bottom bracket.
- Run the tape up the seat tube
- Note the measurement of the centerline where the top tube intersects the seat tube.
- (In the example, this would measure about 19.75 inches)
- Note the measurement to the top of the seat tube.
- (In the example, this would measure about 21.6 inches)
- To convert from inches to centimeters, multiply above measurements times 2.54.
- (Above C-C example: 19.75 x 2.54 = 50.17 cm. Round to 50cm)
- (Above C-T example: 21.6 x 2.54 = 54.86 cm. Round to 55cm)
Well, that’s how to measure a bike frame, specifically a road bike frame. Questions or comments? Feel free to leave them below. – Skippy
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What Kind of Bike Should I Buy
This is the first step because different kinds, or types, of bikes are measured and fit differently.
Your correct size road bike, for example, with a higher top tube (greater C-C or C-t size) and measured in centimeters; whereas, your correct size mountain bike, with has a lower top tube (lower C-C or C-T size) and is measured in inches.
So, we answer what kind of bike should I buy, then we can figure out what size bike you need. Relax, it’s easy! 
Simply answer four straightforward questions which inquire about your riding habits and how you plan to use the bike, they are:
- Where will you ride?
- When will you ride?
- How will you ride?
- What riding position is best (most comfortable) for you?
- An optional fifth question asks about your handlebar preference.
Submit your answers and find the answer on my What Kind of Bike Should I Buy – Calculator page.
Your answers determine your bike riding profile. By matching your profile to the right kind of bike, you receive a personalized report containing what kind of bike to buy suggestions. Once we know what kind of bike, then we can better answer what size bike do I need. – Skippy
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Determining what type of bike you need is the first step in answering what size bike do I need. Why?
This is because different types of bikes have different geometry. I recently posted the article What Size Bike Do I Need – About Frame Geometry which explained some factors of bike geometry and how that effects the bikes riding characteristics; however, the most notable effect of bike geometry variation is riding comfort.
We all want to ride comfortably, but, believe it or not, the definition of comfort would be different from rider to rider and their goals. For example, a occasional recreational rider would have a different definition of comfort than someone who trains almost every day. With that in mind, here are some questions that will help us determine what type of bike will suit you best.
What Type of Bike Do I Need – Questionnaire:
Ask yourself:
Where will I ride?
- Paved roads and bike trails
- Unpaved but smooth trails
- Unpaved and rocky, loose terrain
What riding position would I prefer. What would be most comfortable to me?
- Upright – Upper body upright, almost a chair like position
- Average – Upper body somewhat leaned over, perhaps about 45 degrees
- Aerodynamic – Upper body lower, aerodynamic position, parallel to ground
What are my goals in buying a bike?
- Fitness, losing weight, etc.
- Long distance riding, centuries, etc.
- Competitive riding, racing.
How often will I ride?
- At least once every three to six months
- At least every month
- At least once a week
- Several times a week
- Daily
Consider the above questions honestly and tabulate your answers. In the next post, we will use your answers to determine what type of bike would suit you, then we can better answer what size bike do I need.
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When asking what size bike do I need, I’ll bet the last subject you expected was geometry!
Don’t worry; we are not going to break out the textbooks or complex mathematical formulas. I’ve been out of school a while and forgot most except A = Pi times r squared, but that’s just cause I like pie 
Anyway, geometry in relation to bikes, specifically bike frame geometry, simply refers to the length of the frame tubes and the angles at which they attach to each other. There are three factors we should discuss briefly:
Wheelbase
Definition: Distance between the contact patches (where the tire touches the road) of the front and rear wheels.
Explanation: Imaging turning a short, zippy sports car vs. turning a long, lumbering fire truck. Would you want a fire truck to steer like a sports car or a sports car like a fire truck? No, each one has its purpose. Likewise, if you ride or race a quick bike, the shortest possible wheelbase that still fits you well is ideal. If you want to toddle along on a sandy path riding a beach cruiser, a longer, more stable wheelbase would be preferred.
Head Tube Angle
Definition: Angle (from horizontal) of the head tube.
Explanation: Have you seen a chopper style motorcycle? They typically have long raked fork and a less steep head tube angle. The head tube angle geometry causes the motorcycle to turn slower compared to with a steeper head tube angle.
In short, a frame with a steeper head tube angle will handle quicker, a good characteristic of a high-speed racing bike, but not so desirable for a beach cruiser where stability at low speeds is important.
Effective Top Tube (ETT)
Definition: Distance, measured horizontally, between the top center-line of the head tube to the center-line of where the seat tube would insect.
Explanation: I’m going to describe two different bikes. They both are the same distance between the pedals and the seat, so that fits the same between bikes; however, the distance between the seat and the handlebars on one is short, just long enough that your knee doesn’t hit the handlebars at the top of the pedal stroke, whereas, the second is twice that distance.
Q: What would the effect be on the way the bike fits you?
On bike one, the shorter distance results in a more upright, less aerodynamic, riding position. More upright means more weight over the saddle and less weight supported by your hands and wrists.
On bike two, the longer, more stretched out riding position is less upright and more aerodynamic. Less weight on the saddle means more on the hands and wrists.
Is one fit wrong and the other right? No, there are applications for both. For example, bike one is a typical beach cruiser (comfort at all costs), bike two, a typical racer (speed at all costs).
Q: specifically which of the three geometry factors above play a part in the difference between bike one and two?
Effective Top Tube (ETT); the fit characteristic differences between the two bikes is because of effective top tube length variation.
This example above lists bikes on opposite ends of the fit spectrum, yet there are many frame geometry variations in between. Understanding bike frame geometry basics can help you determine what size bike do I need. Although you measure a bike frame by the seat tube length, the number one factor for proper bike size is effective top tube length since it affects both bike handling and comfort. Use a mountain or road bike size chart or guide to find your ideal fit. Good bike websites have frame geometry charts listed to easily compare different models.
Remember our goal; if your bike is not comfortable, you are not going to enjoy it, so let’s first answer what size bike do I need
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