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,
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.
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.
You will need:
Measuring Tape (If the measuring tape is standard (not metric), you will also need a calculator to convert to metric.)
Well, that’s how to measure a bike frame, specifically a road bike frame. Questions or comments? Feel free to leave them below. – Skippy
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:
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
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:
Where will I ride?
What riding position would I prefer. What would be most comfortable to me?
What are my goals in buying a bike?
How often will I ride?
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.
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:
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