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How to Measure Seat Post Clamp Size

How to measure seat post clamp size

How to Measure Seat Post Clamp Size- Introduction

There may be different reasons why we need to change our bike seats. It may have become worn out because of use, weather, or unexpected events.

We may also want to change it in order to upgrade our bike’s overall design, or because it is not as comfortable as needed for a certain type of ride.

Whatever the cause, it is of great importance to pay attention to measurements so as not to get the wrong one. Should we make an error in this aspect, it may either slip downwards while in use or be too big to fit the seat tube.

In this post, we will focus on the seat post’s clamp size. Ride along with us, and find out what you need to know about this accessory.

What is A Seat Post Clamp?

First, we need to understand the difference between seat tubes and seat posts. The former is the part of the frame where the seat post is inserted. Measures, as you may imagine, vary, but we’ll deal with that later on.

Next, we need to know what a seat clamp is and why or when we should get one. As the name indicates, its main function is to “clamp” or fasten the seat post to the seat tube in the desired height and orientation. Imagine how uncomfortable it would be to feel our saddle sliding or rotating as we ride our bikes!

Seat clamps may be included in the seat tube, as part of the frame. Otherwise, they may be acquired as an external part to add to the seat tube. They look like incomplete collars, attached to their tips by a bolt, used to adjust tension. They may also have a quick-release lever to make it easier for you to remove or modify the position of your seat.

Different Post Measures

As we mentioned earlier, measures vary, and this may cause some headaches if you do not pay enough attention to it.

There are some standard post measurements out there, namely 28.6 mm, 30.0mm, 31.8mm, 34.9mm, and 36.4mm. Differences in the measure may correlate to quality, material, or weight. Nevertheless, other non-standard measures can be found too.

Getting a wrong clamp size will not only affect its function, causing your seat to wiggle up and down, or to rotate sideways. It may also damage your frame. It may slide downwards if it is too big, or crack your seat tube if it is too tight.

How to Measure Your Seat Post Clamp Size

Measuring your seat tube is not a difficult task to perform.

The first thing you need to do is to release the in-frame clamp –if any- to its fullest. In this way, we make sure only the actual diameter is measured. Once this is done, you can either use Vernier calipers, or a “seat post sizing gauge”. These tools come in very handy when deciding which clamp is the correct one for your ride.

Check this video on how to measure your seat post clamp size (credit to RJ The Bike Guy):


Even though some seat tubes may have their measurements imprinted somewhere, or your bike manufacturer may give you this information, it is always recommended to measure it yourself so that you can be sure.