Condensed info: Modern BMX bikes use pivotal seats. To install such a seat on a mountain bike, you will have to replace the existing MTB seat post with a dedicated BMX model.
It’s not possible to install a pivotal BMX seat post on a standard MTB seat post due to the incompatible mounting mechanisms.
What’s a Pivotal Seat?
A pivotal seat allows the rider to adjust its angle.
The seat has three main positions:
- Horizontal
- Pointing up
- Pointing down
Most riders leave their seats either leveled with the ground or pointing up (more common).
A seat pointing up reduces the chances of touching it when performing bunny hops and manuals because the rear of the seat (the most likely point of contact) is as close as possible to the rear wheel.
Additionally, a pointing-up position facilitates the execution of some tricks because the rider can use the front part of the seat as a lever more efficiently. That said, the gains are not “revolutionary”.
The other benefits of pivotal seats are:
1. No bent rails
Pivotal seats do not use rails. Instead, they have a body made of molded plastic with a base that connects directly to the seat post via a single bolt.
The base of the seat and the bed of the seat post have teeth/notches allowing the rider to modify the level of the seat post.
2. Fast Adjustment
The bolt connecting the seat to the seat post can be accessed through the top or bottom of the seat. As a consequence, the rider can quickly adjust the angle of the seat.
Pivotal Seats Are Not Compatible With MTB Seat Posts
A standard MTB seat post has a two piece clamp that squeezes the rails of the saddle.
For that reason, MTB seat posts are compatible only with seat posts that have rails.
If you want to run a pivotal seat, you will have to get a pivotal seat post.
Installing a Pivotal Seat Post On an MTB
BMX frames are made out of steel because the material is tough, resistant to impact and bends before breaking.
Since steel is denser than aluminum which is the common choice for MTBs, BMX bikes have thinner tubing.
Most BMX bikes use seat posts with a 25.4mm/1 inch diameter whereas MTBs rely on 31.8mm seat posts.
If you want to install a BMX seat post on an MTB, you will have to use a shim to increase the thickness of the seat post.
The Length Of The Seat Post
BMX seats aren’t optimized for seated riding. Their main purpose is to serve as something to rest on in-between attempts. For that reason, they’re lowered all the way down to get them out of the way when performing stunts.
As one may guess, many BMX seat posts are made ultra-short (e.g., 13.5cm) to save weight.
A 13.5cm seat post provides insufficient length for riding a modern MTB with a slack geometry and a short seat tube.
Thankfully, longer BMX posts reaching 33-34cm can be found on the market. However, in some cases even that won’t be enough, especially if you’re riding a smaller frame.
To avoid unpleasant surprises, measure how much of your MTB seat post is showing. If you don’t have one, you can use a friend’s bike to get an assessment.
The BMX seat post that you plan on using to install a pivotal seat should be long enough to provide the necessary height while still having its minimal insertion length into the seat tube.
The minimum insertion length is usually 3-4 inches (7.62cm-10.16cm).
Examples:
1. If you need 300mm of height from a seat post that has a total length of 330mm, the combo will not work because the minimum insertion length of the seat post will not be respected.
The aftermath could include a damaged seat post and/or seat tube.
2. If you need 20mm of height from a seat post that has a total length of 330mm, the combo will work just fine.
FAQ: Can I install a BMX seat with rails on an MTB right away?
MTB seat posts are designed for seats with rails, but that doesn’t mean that every rail BMX seat fits.
To know if a BMX seat and an MTB seat post are compatible, you have to take the following measurements:
1. The diameter of the rails
2. The distance between the rails
Some BMX seats have oversized rails for extra strength. Those models won’t fit on a standard MTB seat post designed for seats with 7mm rails.
In addition, some BMX seats are ultra-narrow. The purpose of the design is to minimize the possibility of touching the seat during tricks.
As a consequence, the seats rails are too narrow and non-compatible with an MTB seat post.
What Are The Benefits Of BMX Seats?
Truth be told, BMX seats do not offer amazing advantages over regular MTB seat posts.
The only notable benefit is the ability to pivot the seat, but this quality would be attractive only to people who ride street.
Having said that, some riders (especially those involved in dirt jumping) like the look of BMX components and often try to install them on MTBs.
For example, it’s not uncommon for people to put BMX cranks on an MTB.
The Downsides of Installing a BMX Seat On an MTB
The cons of installing a BMX seat on an MTB are:
1. Pivotal seats are non-compatible with dropper seat posts.
Modern MTBs use dropper seat posts to make riding more dynamic.
However, dropper seat posts have an attachment system that cannot accept a pivotal BMX seat.
2. BMX seats are uncomfortable
BMX seats are not made for long-distance seated pedaling. For extra comfort, it’s best to stick with models designed for actual cycling.
Installing an MTB Seat on a BMX?
Standard MTB seats have rails. To install one on a BMX, you will need a seat post that operates with a clamp.
If your existing seat post matches the requirement, you can bring it to a shop to see which MTB seat would fit.
As mentioned earlier, some BMX seats have rails thicker than usual.
If you own one of those, you will have to use a dedicated MTB seat post because the mounting system on your current BMX seat post won’t allow the switch.
Who’s Lighter?
The table below compares the weight of popular MTB and BMX seats:
| MTB | Weight | BMX | Weight |
| Ergon SM Pro | 235g | WeThePeople Team 2019 | 259g |
| Ergon SM Sport | 325g | Federal MID Roses | 317g |
| 3min19sec Sport | 256g | Federal Logo | 317g |
| Procraft Race Titanium II | 235g | Fit Barstool | 312g |
| Selle Italia Novus Superflow Endurance | 310g | Cinema Waxed Stealth | 334g |
| PRO Stealth Carbon AF | 172g | Fiend Reynolds V2 | 329g |
| Ritchey Comp Skyline Saddle | 265g | Stranger Zefaria | 335g |
| Specialized Phenom Expert | 254g | Profile Logo Slim | 258g |
| Specialized Romin EVO Pro Carbon | 208g | Odyssey AITKEN | 303g |
| SQlab 611 Ergowave Liteville | 150g | Radio Team | 294g |
| PRO Stealth AF | 210g | United Reborn FAT | 221g |
| Average: | 238g/8.39oz | Average: | 298g/10.5oz |
Conclusion: On average, MTB seats are a bit lighter. However, the difference isn’t notable unless you’re using an expensive MTB carbon saddle.
Summary
What You Need To Know
1. Modern BMX seats are pivotal. To install one of them on an MTB, you will need a BMX seat post designed for a pivotal seat.
2. Some BMX seats still use rails. If the thickness and the distance between the rails match that of an MTB seat, you can install the seat on an MTB seat post.
3. BMX seat posts are much shorter than the MTB options. If your frame requires a long seat post, a BMX one may be too short.
4. The only advantage of BMX seats over MTB models is the ability to change the seat’s level (pivot). If you don’t care about this function, you’re better off with a classic MTB seat.
5. If you’re using your MTB for trail riding rather than street tricks, an MTB seat is the best choice.
