How-To Guide: (Correctly Measure a Bike Frame) — Bicycle

If you have any intentions of becoming a professional bike rider, or at most someone who knows their bike, then learning about its measurements is a must, specifically, its frame size. 

You can easily measure a bike’s fit by its frame size. It is easy to measure the frame size. It is the length from the center of the crank axle to the top of the seat tube. This is what accumulates in a frame, and by seeing its measurements, you can easily tell if it will fit you.

Knowing the measurements is also necessary if you plan on buying a new bike. Once you know the different measurements to take into consideration, you’re more likely to find the bike most suited for you. 

This bike will not only be the most comfortable out of your former ones but it’ll also enhance your speed, too. And what matters more than comfort and speed when riding a bike, right? 

Here, in particular, I’m going to go into depth on bike frames. The most crucial part of a bike can either make the bike the perfect fit or a nightmare for you. So what is a bike frame and what does it do? 

You’ll have to read on to find out! 

What You’ll Need To Measure a Bike Frame

Here’s a list of tools you’ll need to measure a bike frame: 

  • Measuring tape
  • A clinometer to measure the angles 
  • A long spirit level 
  • A plumb line 

When you use each tool to measure a bike frame, then only will you get a correct reading. Furthermore, all sorts of bikes are measured in metric units, so be sure to do the same.

Though, some brands still measure in inches, so you’ll have to be wary of that as well. 

A word of advice would be to stick with the metrics, they’re easier to compare and a consistent method. 

» I have covered more on this subject in this blog post: What Bike Size to Get? (Size Charts & Bike Sizing Guide!)

Measure the Top Tube Length

To get an on-point reading, you need to estimate the horizontal cap tube along with the top tube. This horizontal top is called the virtual top and is included in many geometry tables. To measure this, you’ll need to bring out your clinometer and spirit level. This makes sure that the line is in fact, horizontal. 

The most important detail in a bike is its top tube length.

A few years ago, bikes used to have a uniform and horizontal top tube.

However, advancements made it so that it now is sloping for the majority of bikes. 

Stack and Reach 

They measure the vertical distances between two points; the top area and bottom bracket of the head tube. This is the stack. The reach is the horizontal distance between them. This is where your spirit level comes in. 

The majority of bike companies only list the stack and reach values of their bike. These values are easy to measure since they’re unrelated to the frame. 

A pro tip would be to make sure that the blob is symmetrical at both ends and the line slightly falls. This will ensure accurate results. 

You can then line the upper edge of your level with the middle one on the topmost part of the tube.

Move the line slightly until the plumbing line meets the middle of the lowest bracket. Measure the gap between this and you have your reach. 

Measure Angles of the Head 

A clinometer comes into play when you have to measure the angles of the head. If you have a straight tube then it’ll be best to measure your bike’s saddle tube. You can get the clinometer (which is also available as an app on your phone) to line up and then read the measurement. 

These angles are crucial to determine the smooth handling of the bike. The idea is that the more upright angle, the more agile the control. 

A few precautions to take would be to make sure the bike’s in an upright position and the bike is on a horizontal surface. This would ensure accurate results. 

On the other hand, if there’s a kink in your bike’s saddle, then you’ll need a straight rim to correctly follow the lining between the lowest bracket and the top part of the saddle. 

» I have also written this post, about: How Much a Bike Weighs?

The Effect of a Head Tube Length 

Simply put, it’s the length of the front part of the frame where the fork fits. It can either increase or decrease in distance and this is another thing that is attributed to the bike’s frame. Even if it is the same size, a shorter tube will be more aggressive as compared to a longer one. 

This will force the rider to a lowered head position. 

Generally, endurance bikes have longer head tubes for this exact reason. So they can have an upright position and race bikes have shorter ones for the opposite effect. 

This is the main effect a head tube length has on a rider. While it is fairly easy to measure, the number and type of spacers, along with the length of the fork, are all variables that can affect the results. 

Measuring Side Tube Length

A side tube length is a straight distance between the middle of the bottom bracket and the top of the seat tube. To measure this, you have to line up your straight edge with the bottom bracket and the top seat tube. Measure along this to get the best results. 

It may sound easy but it isn’t. This is mainly because some bikes have a considerable extension of the seat tube.

This is between the top table junction as compared to others that use a seat mast. This is why it makes comparisons difficult. 

Additionally, mountain bikes usually have kinks in between the seats, so you’ll have to change your method of following the tube line. 

Measuring the Wheelbase 

Moving onto the wheelbase, your bike’s wheelbase is the distance between the front and rear axles. This is important in the sense that the frame’s ride quality and frame size both depend on each other. 

Despite its importance, it is fairly easy to measure. There are not many steps in finding the value. The only catch is making sure your fork is set straight otherwise, you’ll mess up your measurements. 

Much like the stack and reach, it’s best to repeat the measurement for the wheelbase and get an average for accuracy.

Furthermore, your answers will be correct only if you measure the wheelbase on both sides of the bike. 

Again, take the average and you’re done. The reason we take averages is that it’ll compensate if your fork isn’t straight. 

How to Measure Road Bike Frame Size?

To measure a road bike’s frame size, get the value for your inseam, and then multiply it by 0.7 to get your seat tube length. If your seat tube length is equal to your inseam length then there’s a high chance you’ll have a hard time pedaling.

Multiplying by 0.7 to get the seat tube length is important. This way, you will get a seat tube longer than the inseam, making it easier for cyclists to pedal for long distances.

To understand the dimensions of a road bike, you need to first know that its frame size is measured in centimeters.

To convert it into inches, all you have to do is multiply the reading by 2.54, and there you have your result.

» I have also written this post, about: Between Mountain Bike vs. Hybrid Bike? 

Since road bikes are the most common type of bicycle, their frame measurements are crucial. You’ll spend most of your time on the saddle so comfort should be a big factor. 

How to Measure Mountain Bike Frame Size? 

To measure a mountain bike’s frame, get the inseam length and multiply it by 0.66. It’s best to multiply the inseam length by a smaller number to get the right mountain bike size giving an accurate bike frame size. This is pretty easy, as you can do the calculations on your phone as well. 

Since mountain bikes come with thicker tires, and if you ever want to compare them with thinner, more streamlined bikes like the Mtb will give a higher lift from the floor.

So, always make sure to multiply the inseam readings by 0.66.

Mountain bikes are a bit different, but their frame size is measured in inches, so there’s no need for conversion.

They have smaller bike frames compared to road bikes, as well. This shortness gives riders immense control making them able to maneuver the bike in the toughest of terrains. 

Finding the Right Size For Your Bike 

Now it’s pretty obvious that measuring bike frames cannot be done by just one person. It can get pretty awkward and difficult to balance the bike. If done wrong, you can even fall over. 

This is why it’s necessary to get a friend/salesman’s help. After that’s established and you’ve gotten your bike frame measurement, you can get your ideal bike.

Your measurements must be as accurate as possible and align with other bikes’ values. 

The numbers you’ve at hand should correspond to the ideal bike size for your type. A less complicated method would be to just try it out before purchasing it. Simply sit on it and see if it’s comfortable. 

» Read my blog post about: Women’s Bike Size Chart — (Correct Sizing, Bicycle), click here!

Take it for a ride around the neighborhood and assess if there’s anything that makes you feel uneasy. Plus, you can always adjust the saddle until you notice you’ve to bend your legs to pedal.

Keep going back and forth between measurements until you find one that suits you best. 

Wrap Up

And that’s a wrap! Everything you possibly need to know about bike frames is in one article. Now it may seem useless to many but really, knowing the process of measuring a bike frame can save you from big blunders.

For starters, you can pick a bike that best suits you. So you won’t have to make round trips again and again to get the right bike for yourself.

All you have to do is compare your measurements with the bike, and you’ll know your final pick. 

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