Condensed Answer: A dropper post can be installed on a downhill bike. However, the conversion isn’t very common because as the name suggests downhill bikes are used primarily for extreme descents.
Or in other words, the main terrain eliminates the need to have the saddle at an optimal position for pedaling.
Requirements For Installing a Dropper Post On a Downhill Bike
1. Compatible Size
The dropper post should be compatible with the seat tube of the bike. If the dropper post is too wide, the rider won’t be able to install it. If it’s too thin, it will wobble.
The second scenario is better because it’s possible to make a thinner seat post compatible by using a shim.
In most cases, downhill bikes use 31.6mm diameter seat posts.
Nonetheless, it’s still recommended to remove the current seat post and check the size marking on it. If it’s absent, you can use a caliper to measure the seat post’s diameter.
The size of the dropper should correspond to the size of the current seat post.
2. Sufficient Length
The dropper post should provide the height needed for comfortable pedaling.
To determine whether a dropper post is up to the task, one can use the following guideline.
- Elevate the current seat post to the point where the rider can extend their knees sufficiently.
- Measure the seat post section showing above the seat collar.
- Deduct the minimum insertion length of the considered dropper post from its total length.
The final number should be equal or greater than the length of the rigid seat post section showing above the seat collar (the previous measure).
Measure 1 = 300mm (the seat post section above the collar)
Measure 2 = 530mm (the total length of the dropper post)
Measure 3 = 150mm (the minimum insertion length of the dropper post)
Conclusion: This particular dropper post provides the necessary elevation for more comfortable pedaling.
The Benefits Of Installing a Dropper Post On a Downhill Bike
The purpose of a dropper post is to allow riders to lower the seat before a technical descent and then quickly elevate it upon reaching a flat surface or a hill.
The elevated position makes it possible to fully extend the knees and transmit more power to the pedals without having to stand up.
Therefore, a dropper post makes downhill bikes more versatile.
- Easier Climbing
Climbing with a lowered seat post is highly inefficient and tiresome. By pushing the seat post up, the rider will make the experience more manageable.
That said, downhill bikes have a poor geometry for climbing. Lifting the saddle helps but doesn’t fully compensate,
The Downsides of Installing a Dropper Post On a Downhill Bike
- Extra Expenses
A quality dropper post isn’t cheap. When you add the base price of a downhill bike, the bill becomes quite high.
And since dropper posts aren’t essential for pure downhill, it will be wiser to either save the extra money or invest it into a more important component (e.g., fork, brakes…etc.) that will have a greater impact on pure downhill performance.
- Potential Technical Issues
The rear shock of downhill bikes has lots of travel. The cable controlling the dropper may interfere with it if the component isn’t properly installed.
- Extra Weight
Dropper posts weigh more than standard seat posts. Thus, the rider will be adding extra grams to a machine that’s already heavy. Nonetheless, this isn’t a major concern because downhill bikes don’t have to be super light.
Cheaper Alternative Solutions
- Quick-release seat posts
Another option would be to simply equip the bike with a long seat post and a quick-release collar. This will allow you to quickly lower the seat post before a descent and extend it for a climb back up.
The obvious downside of this practice is that the switch from descending to climbing will be a lot slower.
Tip: Use a permanent marker of vivid color to mark the top and bottom position of the seat post. Those indications will greatly speed up the process.
Summary: What You Need To Know
- A dropper post can be installed on downhill bikes as long as it’s compatible with the seat tube.
- The selected dropper post should be sufficiently long to elevate the saddle for comfortable pedaling.
- A dropper makes it easier to pedal a downhill bike uphill but can’t compensate for the geometry of the bike which simply isn’t designed for ascending.
- The main downsides of a dropper post are its complexity and extra weight.
- A less convenient but much cheaper solution would be to use a long seat post coupled with a quick-release clamp.