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How do I select the best post for my bike frame and height?Updated a year ago

A properly sized dropper post can completely change your ride for the better. Obtaining optimal saddle height with the push of a lever  can help improve pedaling efficiency and make for easier climbs. At the same time, maximizing the travel of your dropper can help move your saddle as far out of the way as possible during descents, which means you’ll have a safer outing. Knowing how to size a dropper post is the first step towards improving your ride and having more fun on your bike, so let’s hop to it.


To get started with finding your ideal dropper post size, you first need to find your proper saddle height (if your saddle is already at your desired height skip ahead to the next section of this article). Setting your saddle height may take some time as it is largely based on personal preference and depends on the length of your legs. However, a good rule of thumb is that your heel should maintain contact with your bottom pedal while your leg is fully extended without forcing you to lean to one side. This way, when you’re pedaling on the ball of your foot you know there will always be at least a slight bend in your knee. Setting proper saddle height is important as it helps prevent joint and muscle pain while also allowing the rider to generate the most efficient pedal stroke. 

If you’re unable to fully extend your legs while pedaling, try raising your saddle in small increments until you are comfortably able to do so. If you find that your hips are rotating from side to side to maintain contact with your pedals while pedaling, try lowering your seat in small increments until you are no longer leaning. Repeat these steps until you find your sweet spot.


Now that your saddle is set to the most efficient height, let’s get to measuring for your future dropper post. We’ll be looking for three numbers, in particular, that will impact the size of your future dropper post: full extension, max insertion, and overall length. Before we get out the measuring tape actuate your dropper so it is fully extended.


As can be deduced from the name, full extension is the height of your saddle when your dropper post is fully extended, and, ideally, it’s the same saddle height that you will use when climbing. Don’t worry, this measurement still applies to you if you don’t currently have a dropper post. To find full extension, grab a measuring tape and measure the distance between the top of the seat collar to the center of the saddle rails.

How to Size a Dropper Post with PNW Components


Full insertion represents the distance your seat post can be inserted into your bike before it is obstructed. Examples of obstructions are kinks/bends in the seat tube (such as the one in the Marin Alpine Trail 7 frame pictured below) water bottle cage bolts or suspension linkage. To find full insertion, measure from the top of the seat collar to the top of anything that would obstruct your dropper post’s insertion.

How to Size a Dropper Post with PNW Components


You probably guessed it, but maximum overall length refers to the maximum length your new dropper post can be if you’re trying to replicate your current setup. Maximum overall length is calculated by adding the previous full extension measurement with the full insertion measurement. Purchasing a dropper post longer than this measurement means the post will either not fit your bike or there will be extra travel you cannot use. If the latter is the case, you will be continually estimating your proper saddle height while riding, which is not a fun experience and can lead to serious discomfort and muscle fatigue.


When it comes to choosing the proper dropper post size we have two options for you: consult the sizing charts that we've placed on each of our dropper post product pages, or use our custom Dropper Post Calculator. The second option is much easier and ensures greater accuracy, but we’ll talk about the sizing charts first in case you don’t trust computers.


If you've checked out our dropper posts before, then you’re most likely familiar with the sizing charts. For those of you that aren’t, they look like this:

How to Size a Dropper Post with PNW Components

To use the chart to choose the correct size dropper post, we need to use all three of the measurements you took earlier. In order for your new dropper post to replicate your current setup, the three numbers you calculated earlier must not exceed the corresponding numbers in the size chart. Your calculated maximum overall length must not exceed the chart’s “Total Length,” your measured full extension must not exceed* the chart’s “Seat Collar to Center of Rails,” and your measured full insertion must not exceed the chart’s “Full Insertion Length.”

*The 30mm of tool-less travel adjust in the 3rd Gen. Rainier gives you some wiggle room. Your future Rainier’s “Seat Collar to Center of Rails” figure can exceed your full extension measurement by a maximum of 30mm. 

Let’s use the measurements from the Marin Alpine Trail 7 as an example and act as if we’re going to replace its current dropper post with a 3rd Gen. Rainier. The measured full extension is approximately 205mm and the full insertion is approximately 230mm, which means the maximum overall length is 435mm. The maximum overall length and full insertion are both below the corresponding numbers for the 3rd Gen. Rainier’s 150mm travel option, while the full extension is actually longer than the 150mm option’s full extension. However, this isn’t an issue as the new Rainier comes equipped with 30mm of tool-less travel adjust which would allow us to reduce the full extension to the appropriate length.


Math is hard. Accepting defeat when you accidentally order the wrong size product is even harder. We want to help you find the right-sized dropper post on the first go; so, we teamed up with a private developer to create our industry-leading Dropper Post Calculator. It’s located on all of our dropper post product pages right by the sizing options and is incredibly easy to use.

How to Size a Dropper Post with PNW Components

To use the Dropper Post Calculator, first click on the “Try Our Dropper Size Calculator” button on the product page of the dropper post that you’re looking to purchase. It’s important to note that each calculator is created with the dimensions of a particular dropper post in mind. For instance, if you’re using the Dropper Post Calculator on the Pine 27.2 Dropper Post page it will only calculate your size for the Pine 27.2 Dropper Post. 

Once the calculator is open, you’ll notice that in addition to your full extension and insertion measurements, you also need to know your bike’s preferred seat post diameter. You can find this information either on your frame manufacturer’s website, or stamped onto the bottom of your current seat post. 

After you have the diameter of your seat post, simply enter the diameter, full extension, and full insertion measurements into the appropriate fields. Then click “Calculate”, and voila! The recommended size for your preferred dropper post appears above the “Calculate” button, which has now turned into a “Buy My Size” button. In the case of the 3rd Gen. Rainier, the Dropper Post Calculator will even tell you how much travel adjust to use to perfectly reach your desired saddle height.


How to Size a Dropper Post with PNW Components

To exit the Dropper Post Calculator and continue shopping, you can either click the “Buy My Size” button, which will immediately add the calculator’s recommended size of your preferred dropper post to your cart, or use the “X” in the upper right-hand corner. From there it’s back to shopping as usual and you can either manually add your new dropper post to your cart, or move on to our other products for some more sizing wizardry.

Best of luck on your search for your new dropper post. If you're unsure of which dropper post is right for you, check out our recent article that teaches you How to Choose a Dropper Post

If you need help in finding the perfect dropper post size for your set up, we’re more than happy to lend a hand. Feel free to reach out to our incredible Customer Service team at [email protected] and we’ll work to get you back on your bike in no time.

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