Yes dropper posts are installed on downhill bikes but it does not give a positive ride and you will not stay comfortable with the dropper post, their height is greater than the normal saddles and seats, and the angle of the dropper post and the handlebar does not remain accurate with this setup and if your height is small, your feet’s doe not be placed well on the pedals, further you need to install clipless pedals to provide better gripping when your shoes start striking on the pedals to produce rotating torque, and also the cables of the dropper post are much irritating on downhill bikes, because DH bike frames are not made for dropper posts and their cables, there are few categories of downhill bikes which have external cable routing, but those bikes which have internal cables routings, you have to make a track and way within the frame on them to pass the cables of the dropper post towards the front direction.
Pedaling Position:
The direction and position of your pedaling will also change, and in those parts of DH trails where pedaling is needed, you can easily strike your pedals by sitting in the straight upward direction on a dropper post, and also you will make a better grip on a bike by pushing your feet on the pedals with a force.
Sitting Position:
Normal saddles and seat posts will feel like you are sitting on the saddle making an angle of 90 degrees but with dropper posts installed on a DH bike, it will change the angle of the sitting position and your height will raise from the normal bike seats. you can easily increase or decrease the height of the dropper post for comfortability and a smooth ride.
Difference Between Quick Release And Dropper Posts On DH Bike:
Dropper posts usually divert all the attention of your mind when you’re coming down on the trails because you are continuously raising and lowering the height of the dropper post, but quick-release dropper posts are worth and a better choice on DH bikes, because just a single time you will increase or decrease the height of the saddle and it remains in the same position, all of your focus will be in front on the trails.
Dropper Posts Are Better For Longer Rides:
If you are racing and your trails have more than 100km of distance, then you will easily get fatigued and tire in the middle of the trails with normal seats and saddles, and also in racing, every second is important, so quick-release dropper posts need much more time in giving an appropriate height to seats, but dropper posts would prevent much of your time by sitting and in riding position, you can easily maintain the height of the saddle by dropper post on DH trails.
Dropper Post Insertion Within The Seat Tube:
DH bikes are not specific bikes for dropper posts and the seat tubes of these bikes do not have enough hollow space for the insertion of the long tube dropper posts, dropper posts would not stay deep within the set tube of the DH bikes, so you have to stretch seat tube of your bike or make enough space for a dropper post to stay tightly with the tube, but there are few DH bike frames which are compatible with the dropper posts. before buying a new dropper post for your bike, measure the diameter and width of the dropper tube and the seat tube diameter with the help of a caliper.
Angle Of The Dropper Post And Top Tube Of Frame:
Dropper posts are straight in a raised position and these are not recommended for longer rides because the seat joint place where chain stay tube, seat tube, and top tube frames are meeting with each other at an angle, a large number of pressed forces which are coming down toward the saddle of the dropper post are reaching at that joint, due to which all the stress and force of the frame would directly at the joint of the frame and when time passes this joint starts becoming weak and crack easily, to avoid the lugged joint from cracking and breaking, avoid longer tube dropper posts for longer rides on daily basis.
Dropper Posts For Jumps And Drops:
Dropper posts are not installed on those trails which contain enough drops, jumps, and whipping trails, due to their enough height, there is a specific seat height for jumpy trails which is adjusted and attained by unscrewing the quick release of the saddle for these kinds of trails.
Weight Issues:
Dropper posts have enough weight and these are heavier than quick release and normal saddles. so if you are coming downward, these would not cause any big difference, but if you are climbing upward then dropper posts are not recommended due to their heavier weight.
Conclusion:
If your bike is heavier than ever use dropper posts on downhill bikes, and mostly DH bikes do not have internal routing for the insertion of the cables of the dropper post, if you are comfortable with the external routing of the dropper posts, then it better to install it in your bike, and also dropper posts depends on the trails if your trails are 70% downhills then install gravity dropper post in your downhill bike.