SEATS & SEAT POSTS
There are four types of seats in bmx. Rail, Pivotal, Combo and Tripod.
RAILED SEAT
Features a metal lock and springs. Rarely used today due to it's heavy weight. Main advantage is that with rail seat you are able to adjust the seat's position in all directions (set up the angle or move it forward/backwards) unlike the other seat types.
PIVOTAL SEAT
The pivotal seat is a lot harder to break, way easier to adjust, more lightweight plus it looks smoother. Pivotal became very popular among riders and recently it is the most common seat type in BMX.
COMBO SEAT
The seat + Seatpost are connected together. Main advantage of combo seats is low weight. Usually seen on complete bikes.
TRIPOD SEAT
Simple, yet stronger seat using 3 points of support (Hence the Tripod name). When flybikes introduced this system it had a big impact on a lot of companies who later decided to redesign their seats with tripod system as well.