Speedups are entity tiles that alter the speed of any tees inside of them. Speedup tiles share the same hitbox dimensions as a standard DDRace tile. The behavior of speeders depends on whether it has a max speed value or not.
Speeders Without Max Speed
Speeders without max speed simply add velocity to a tee. (However, speedups won't let a tee go past the maximum horizontal speed)
Speeders With Max Speed
Speeders with a max speed value often behave differently - in many cases, they allow a tee to perform speed bugs with relatively easy setups.