If you don’t know how to calculate Seatpost size, replacing your bicycle dropper can be a daunting task. The importance of a good Seatpost in achieving a comfortable ride cannot be overstated. It also improves your bike’s aerodynamics and usability. The Seatpost is one of the most underappreciated parts of the bike, despite its importance in terms of efficiency and performance. The improper size not only ruins the bike’s frame but can also cause back pain. So, how do you figure out what size Seatpost you need to avoid all of this? We’ve put together a step-by-step guide to show you how to properly measure your saddle post so you can get the most out of your workout.
To figure out the right size, you first need to find your top tube length. This is the horizontal tube that connects both your seat and your handlebars. It’s generally measured from the center of the bottom bracket to the top of the seat post clamp. Once you have an accurate measurement, all you have to do is look for a post with a similar, if not identical, measurement. There are multiple brands that manufacture bicycle droppers, and each brand has its own sizing chart available online and on its packaging.
Table of Contents
- How to Determine Seatpost Size?
- Step 1: Look at the Old Seatpost
- Step 2: Measure Your Saddle
- Step 3: The Diameter of Your Old Seat Post Should be Measured
- Step 4: Determine the Diameter of Your Seat Tube
- Step 5: An Internal or External Routing
- Step 6: Determine the Travel Needed
- Step 7: Determine Your Maximum Extension
- Step 8: Calculate the Minimum Insertion
- Step 9: Calculate the Total Length
- Step 10: Make use of the Seat Post-Sizing Rod
- Types Of Seat Posts
- Are All Seat Posts the Same Size?
- What Seat post Size Do I Require?
- Is it possible for the Seat post to become stuck if it is the wrong size?
- Is it possible for a Seat post to be excessively long?
- How do you fit a new bike seat?
- Is it possible for a Seat post to be excessively high?
- Is it possible to break a Seat post?
- What size Seat post clamp do I need?
- Is it permissible to cut a bicycle Seat post?
How to Determine Seatpost Size?
The seat post is one of the most often ignored components of a bicycle. Not only can choosing the improper size harm the frame, but it may also result in back discomfort. How do you determine the length of your saddle post? We’ve created this how-to guide to demonstrate how to determine the depth of the hole so you can avoid being fixated on extension numbers that may confuse you and make it harder to lower your seat post.
Step 1: Look at the Old Seatpost
A seat post is a metal or carbon fiber pole on which the saddle sits. A saddle may be mounted either on the seat post or on a seat tube, which is part of the bike’s frame. A bike can have either one seat post or two-seat posts on the front and on the rear of its mainframe.
It may seem self-evident, but glancing at your existing or previous saddle post can help you determine the seat post size. This is the most straightforward method for determining the size of your dropper. If you want to replace your Seatpost but aren’t sure how long it should be, take out your old one and measure it. Near the end of the insertion line, the sizes are frequently stamped, or laser marked. The figures are in millimeters.
Step 2: Measure Your Saddle
Before you measure your Seatpost size, you need to check the current measurement of your saddle. Using a measuring tape, measure from the center of the saddle to the bottom bracket. If you don’t know where this is located, look at the bottom bracket shell of your bike.
This is where your pedals attach to your frame. Now subtract 2 cm from this length and write it down on a notepad or piece of paper. It’s important to have this measurement handy when calculating your new Seatpost size. If you are measuring your bike for the first time, you might not be aware of where the center of your saddle is located. To find it, simply place the tape on the tree, which is where most saddles connect to the frame. Put one end of the tape at one edge of your saddle and measure till you get to the other side, keeping it centered on your saddle. Now subtract 2 cm from the length and write it down on a notepad or piece of paper.
Step 3: The Diameter of Your Old Seat Post Should be Measured
Once you have all your measurements, you can now determine the seat post size. In order to do this, you need to find the diameter of the Seatpost. The markings can be obliterated due to age and friction. So, how do you figure out what size dropper you need? This is where we get our hands dirty and take measurements. To examine the diameter of the existing seat post, use a digital caliper and metric calipers to measure the diameter of the post.
To begin, if you have an old saddle-post that is securely attached, you can measure its outer diameter to get an exact approximation of what you will need to purchase. If the existing seat post is worn out and you can’t make any realistic predictions from it, move on to the next stage, where we’ll show you how to measure the seat tube to figure out the correct seat post size. After you have your measurements, you can calculate the diameter of the post at the lowest point where it meets the seat tube. The lowest point is called a “threaded bottom.” It’s a portion of a seat post where you can see the seat tube and where most seat posts attach to it.
Step 4: Determine the Diameter of Your Seat Tube
How do you determine the size of your bicycle seat post if you don’t already have one? The Seatpost is held in place by a seat tube, which is a frame. To put it another way, it’s the location where the seat post is attached. When measuring the seat tube, keep the internal diameter of the area where the seat post will be put in mind. Make sure you don’t measure the external diameter because that won’t help you figure out what size Seatpost you need. To find the bottom, take the tape and run it from the center of your seat post to the bottom of your seat tube. What’s left is a tape measure with a measurement in millimeters.
To find the inner diameter, take another piece of tape and place it against one side of your seat post. Place another piece on top of this one to make sure you measure the correct amount. Once you have found this measurement whose length is 2 cm shorter than that of your old Seatpost, write down this number. A Vernier caliper is recommended for measuring the diameter of the seat tube.
Step 5: An Internal or External Routing
Seat-post cable routing might be internal or exterior. Internal routing (affectionately referred to as stealth) is the most often used method of cabling in mountain bikes. The Seatpost is connected to the remote level at the post’s shaft through internal cable routing. On the other hand, external cable routing involves routing cables around the exterior of the tube and attaching them to the shaft or head of the post. The routing of your bike will dictate the sort of seat-post size you choose.
Step 6: Determine the Travel Needed
The length of the dropper is the next important consideration when choosing a seat post. The dropper’s length is always measured when the post is fully extended. This is easy to do when you already have the measurement of your bike’s Saddle Post. Just subtract 2 cm from this measurement and write it down on a notepad or piece of paper. Now, to find the length, measure the distance between your bottom bracket (which is where your pedals attach). This is called the “top tube length.” To find the total distance that the Seatpost extends, find this distance between two points near each end of both ends of your post.
Subtract the difference of this distance from the measurement you took of your old seat post. This difference will be close to the length of the new dropper post you need. Always check out what is available in your area before making a decision about what size Seatpost to install so that you aren’t stuck borrowing one. You must also know how many drops you require.
Most bikes will have a 100-150 mm clearance. It is recommended that you travel as much as possible. This means you have the ability to shift the seat around and lower it for added comfort and enjoyment. In the end, you want a seat post that keeps your saddle in a good position for cycling. When choosing a seat post, make sure it doesn’t leave the seat too high even when fully installed in the frame.
Step 7: Determine Your Maximum Extension
To precisely measure the size of the seat post, you must first determine the height you desire when your seat is fully extended. This is done by measuring the seat from the collar to the seat rail’s center. When choosing a post, keep in mind that too much length can reduce efficiency and power transfer while cycling. Your ideal extension is one that allows you to drop the seat for added comfort and enjoyment. You don’t want to be looking at the post while you are riding.
The length of the extension is measured in millimeters. If you are using metric measurements, it will refer to the distance between the two points where the extension will be fixed when it’s fully extended. To find this measurement, take a string or elastic band and wrap it around your Seatpost before fixing it into place. This measurement will indicate how much the saddle can be lowered during riding without damaging your suspension system.
Step 8: Calculate the Minimum Insertion
How far can your Seatpost be inserted into the frame? You may figure out your size by measuring from the top of the saddle collar down to the point where you don’t think there’s any more room. Knowing the minimal insertion is important because it prevents you from focusing on extension numbers, which can lead to confusion and make it difficult to adapt your post to lower points. Calculating the minimum insertion is also useful since you want it to be as close to zero as possible. Because most saddles are somewhat low by nature, riders with or without knee problems can use their saddles without worrying about the post bottoming out.
However, some saddles are set up so that they sit higher than desired, so your adjustment must be arranged to avoid bottoming out if you ride with a very high-volume saddle. The way that you find the minimum insertion is by subtracting the length of your seat post from your seat tube’s internal diameter. This number indicates the amount of insertion, but it isn’t always all you need to know. Now you have to be aware of how much distance is left between the top of the seat collar and where you think there isn’t any more room for insertion.
This measurement is called ” throw.” It’s the distance between the center of your post and your saddle rail. The higher you place your saddle, the more space you’ll need. If it’s less than 3 cm, you won’t need to worry about the post rattling on rails. But for riders who use high-fire road saddles made by Cervelo or Santa Cruz, something extra must be done. You can reduce the distance by attaching a K-strap between it and where your seat rail attaches to the frame. It’s important to leave the post long enough so that you can easily lower your saddle for comfort, but not so much that it could interfere with your aerodynamics.
Step 9: Calculate the Total Length
When deciding the size, the total length of the dropper is critical. Seatposts come in a variety of lengths, so if you’re shopping for one, be sure the length is right for you. A short post can be inconvenient and inadequate for ergonomics. Seatpost lengths typically range from 75 mm to 400 mm. Short Seatposts are lighter but less adaptable, whereas longer Seatposts are more versatile. Most mountain bikes, based on my observations, have longer seatposts, which make them easier to adjust for uphill and downhill terrains, as well as safe and injury-free.
Step 10: Make use of the Seat Post-Sizing Rod
How else can you determine the diameter of a Seatpost? There are a few more options for determining the size of your seat post. The usage of seat sizing rods is one of them. To determine the diameter, position the rod into the seat tube and compare the diameters. The rods are designed to expand in diameter from one end to the other. As a result, the accurate reading is the one above the end of the seat tube. You can also use the method of string to determine the diameter. Just make sure that you use a string or elastic band to measure your seat’s height. Wrap it around the Seatpost and compare it to the diameter.
The last option is by using a measuring tape, which you can find in most hardware stores, or you can use one that is laser-aligned. It will measure your seat tube’s circumference, which you will then subtract from your total length measurements. With these four measurements, you now know how long it is, and you can set the maximum and minimum insertion. With this information and a little practice with using different seatposts, getting it right will be easier than ever.
Types Of Seat Posts
Seat posts come in a variety of styles and sizes. Numerous older bicycles, for example, have what is referred to as a “simple” Seat post. The seat post’s diameter narrows toward the top, where a single bolt tightens a clamp that secures the saddle to the post. This style has gone out of popularity in recent years. The following are the most frequently used varieties of seat posts today.
Seatpost with an Incorporated Micro-adjust Clamp at the Top
The most popular configuration is a stiff Seatpost with an incorporated micro-adjust clamp at the top. This clamp attaches to a saddle’s rails through one or two hex bolts, allow for quick and easy saddle modifications. The micro-adjustable Seatpost design has the benefit of being simple, light, and adjustable, as the name indicates.
Suspension Seat Posts
Suspension seat posts are quite prevalent on hybrid and mountain bikes since they have an integrated shock absorber that helps smooth out uneven roads and terrain. This form of Seatpost is often persistent and has fewer sizing possibilities.
The Dropper Post or Adjustable Seatpost
The dropper post, or adjustable Seatpost, is another kind of Seatpost that is popular for mountain biking. Adjustable seatposts use internal cable routing to enable cyclists to lower their seats without dismounting and using a quick-release device when providing rough terrain.
An Integrated Seatpost
Aerodynamics and lightweight are key features of high-end time trial or triathlon bikes. The majority of these bikes include an aero Seatpost that is intended to complement the aerodynamic form of the frame’s tubing. While the majority of the other seatposts described earlier may be used on a broad range of bikes, aero seat posts are often only compatible with a single frame type. Certain TT/tri bikes lack even a separate Seat post. Rather than that, the seat tube is a single segment that supports the saddle. This is referred to as an integrated Seat post.
Are All Seat Posts the Same Size?
No, seat posts come in a variety of sizes and can be adjusted in a variety of ways. The diameter of the seat post does not necessarily indicate how far it may be lowered or how long it is. You must determine the depth of the seat post and the length of the seat post. The diameter of the seat posts ranges from 22 to 35 millimeters in 0.2 millimeter increments. The most common size is 27.2 mm (1.07 inches), which is seen on the majority of motorcycles, particularly high-quality models. For added robustness, larger diameters such as 30.9 mm are used in certain contemporary bicycles, along with thicker aluminum or carbon tubing.
The depth of the seat post is measured from the top of the seat tube, which is visible once the saddle has been removed. The depth is normally between 30 and 60 millimeters. The majority of bicycle saddles have a sloping front edge, so if you pull up on them at the front or rear, they will not slip out.
What Seat post Size Do I Require?
The size of the dropper is determined by your requirements. However, you should be aware that the size of your post can affect your bike’s efficiency and comfort. For example, a larger post stiffens a bike while improving power transfer when pedaling. A narrow post, on the other hand, is more comfortable on a rough surface. Finally, for a perfect snug fit, you’ll need a Seat post whose diameter matches the diameter of the seat tube. According to industry standards, the most common diameter that fits most bike frames is 27.2 (standard) and 30.9 or 31.66mm.
Is it possible for the Seat post to become stuck if it is the wrong size?
Sure. Seat posts might become stuck due to faulty installation or the incorrect size. There’s no need to shove the post in if you get the appropriate size. A large dropper will require you to press it down, resulting in a bulge in the seat tube, whereas a tiny dropper will require you to overtighten its bolts, resulting in a deformation: this is what causes the post to become stuck.
Is it possible for a Seat post to be excessively long?
You will be structurally safe as long as the minimum length is fitted into the frame. Of course, you can purchase a shorter post. However, if you have to drop the saddle all the way to the frame, the bike is probably too big for you and maybe unsafe because you won’t have enough standover space.
There’s a common misconception that the minimum insertion should be the same as the minimum length. So if you have a post that is 100 mm long and has a maximum insertion of 130 mm, there’s no need to adjust the saddle. This is not true at all. In fact, if your saddle is adjustable, then you should use your saddle to set the correct amount of insertion for a proper fit.
How do you fit a new bike seat?
When fitting a new seat, you’ll need to make sure that there’s at least 1 cm of clearance between your bottom and the saddle. The test for this is sitting on the saddle and making sure that there’s enough room for your sit bones (saddle suspension) without any pain or discomfort. Make sure your knee is slightly bent when riding. If you’re experiencing knee or hip pains while riding, then you might want to examine whether it’s related to your saddle position.
The saddle should not be too far forward. When doing this, cyclists with very low body sizes can experience discomfort and pain in their lower back and pelvis. This is due to the lack of forefoot and midfoot clearance with the bike’s top tube and stem combined with the increased torque from gravity. This particular issue might also occur if you have a Seat post that is set quite long as well as a seat that is set quite high.
Is it possible for a Seat post to be excessively high?
It’s actually quite simple to set the saddle height. The saddle height is determined by the proper amount of insertion, and it varies from person to person. What you need to do is change the seat until it’s comfortable for you, and this will require a few practices. The best place to feel for this is at your hip bones. People with a shorter torso and shorter legs will find that cycling with their seat slightly lower or at their hip bones provides them more comfort and power transfer whenever they’re pedaling.
Is it possible to break a Seat post?
Yes, a Seat post can break if it is excessively used or misused. Seat posts are very strong and strong, so it’s unlikely for such a thing to happen. If you use your bike frequently and if you frequently keep your bike in the same position, then the Seat post will likely break, especially if it’s a lower-end Seat post. However, this is a rare occurrence. If you’re using your bike frequently and you’re not seeing any problems with your Seat post, then there’s no need to change anything.
What size Seat post clamp do I need?
I’m not sure what size Seat post clamp I’ll need. Note that the seat clamp should be the same diameter as your seat tube, not your Seat post, which is a little smaller. For example, a 27.2mm Seat post (which is popular on-road cycles) fits inside a 28.6mm seat tube. Thus you’ll need a 28.6mm clamp.
Is it permissible to cut a bicycle Seat post?
The right method to accomplish it is to cut the post down. Seat posts, on the other hand, must have a minimum amount of tube in the frame for safety reasons, so take some measurements and cut off as little as you can, filing down any rough or sharp edges. Bicycle seatposts are mostly used by bicycle commuters. From their standpoint, seat posts are most efficient when they are mounted at the most comfortable spot for the rider. A Seatpost usually comes with adjustments to ensure optimal comfort for different body types. A saddle post can be adjusted to suit individual preferences.