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How To Measure Bike Frame For Frame Bags?

We often get a question from newbie bicyclists- “What size frame bags will fit my bike frame?” You have to measure properly to know if your best bike frame bag will fit the bike. So, how to measure bike frames? That’s what we’ll be talking about.

Bikes are usually measured by their frame size. Whether it is a road bike, mountain bike, or touring bike, the frame bag is the most basic bike luggage piece. So, getting an accurately fitted frame bag is important.

Modern bikes come with sufficient information about the exact measurements of the frame. So it is generally not necessary to measure the frame size yourself. If there is no information added, don’t worry, you can still measure the frame.

Without exaggerating, let’s find out how and what to measure.

What to Measure in a Bike Frame for Frame Bag?

Many key factors define a bike. They are;

  • Top tube length
  • Seat tube length
  • Wheelbase
  • Head tube frame (L/XL)
  • Front center
  • Downtube length
  • Reach and stack
  • Chainstay length, etc.

You can measure each of these factors to know if the bike is the correct fit. When it comes to measuring for frame bags, it is not necessary to measure each element. You’ll need to measure the top tube, seat tube, and downtube length.

How to Measure Bike Frame for Frame Bags?

The measurement of bikes varies from bike to bike. Most mountain bike frames are measured in inches, while road bikes are measured in centimeters. Even there are some brands like Moots that measure in both units.

Nowadays, you can find a geometric chart of the bike frame sizes on the manufacturer’s site. It is worth checking your model size exits on the site. If there is no information available, you can find the exact measurement for your frame bag.

As mentioned, you only need to measure the top tube, downtube, head tube, and seat tube length. To do so, all you need is-

  • A tape measure.
  • A long spirit level.

How to Measure Top Tube Length?

The top tube length is the horizontal distance from the bike’s head-tube joint to the seat tube. These days, bikes are designed with sloping top tubes. Usually, the manufacturers include the real top tube length in a bike geometry table.

But measuring the real top tube doesn’t give a consistent measure. So you need to measure horizontal top tube length, which is called effective top tube length. Effective top tubes are one of the three ways for defining the length of the bike’s front triangle.

Use a spirit level to measure the top tube length and make sure it is really horizontal. Most bike manufacturers size their bikes with top tube length. However, it is not true when it comes to mountain bikes.

How to Measure Head Tube Length?

The head tube is what contains the headset. It has two key measuring factors: the head tube angle and the head tube length. The angle is not necessary to measure the frame for frame bags. You only have to measure the length.

The head tube length is attached to the top tube and the downtube. Besides, it is measured from the bottom to the top of the bike’s head tube. You can use a tape measure to get an accurate reading. Usually, a long head tube raises the front edge of the bike.

How to Measure Seat Tube Length?

The seat tube is a roughly vertical frame in a bicycle. The straight line distance between the top of the seat tube and the bottom bracket center denotes the seat tube length. Measuring the seat tube length is critical.

Some bikes come with a huge extension above the top tube joint, while some use seatmast. Especially mountain bikes include a bend in the seat tube. It is not necessary to follow the line of the whole tube.

Instead, you can measure either from the center of the bottom bracket to the top tube and seat tube’s joint. It is called Center-to-Center or C-C. Else, measure along the center of the bottom bracket center to the seat tube’s top (Center-to-Top).

How to Measure Downtube Length?

The downtube length is the joint between the head tube and the bottom bracket. It denotes where your hands will be compared with your feet. Measure the downtube using a measuring tape.

Final Words

Thus far, you’ve learned how to measure the bike frame to fit your frame bag. Isn’t it too easy? Now you’ve all the measurements to evaluate what size frame bag you need. So get your frame bag now and explore your favorite trails with a bike.

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