Minecarts go down spirals slowly

When pushing a minecart down this spiral, it goes down slowly compared to when the Minecart Improvements experiment is disabled.

Steps to reproduce:

1. Create/open a world with the Minecart Improvements experiment enabled
2. Build a spiral:
   
3. Place down a minecart at the top and push it down the spiral

Observed result:
The minecart goes down the spiral slowly.
With Minecart Improvements.mp4

Expected result:
The minecart goes down the spiral quickly, like when the Minecart Improvements experiment is disabled.
No Minecart Improvements.mp4