diff --git a/y2019/control_loops/python/drivetrain.py b/y2019/control_loops/python/drivetrain.py
index b0a213b..e2d6eec 100644
--- a/y2019/control_loops/python/drivetrain.py
+++ b/y2019/control_loops/python/drivetrain.py
@@ -18,10 +18,10 @@
 # Encoder is on a 24 tooth gear attached to the output gear.
 
 kDrivetrain = drivetrain.DrivetrainParams(
-    J=4.0,
-    mass=40.0,
+    J=1.5,
+    mass=38.5,
     # TODO(austin): Measure.
-    robot_radius=0.616 / 2.0,
+    robot_radius=0.45 / 2.0,
     wheel_radius=4.0 * 0.0254 / 2.0,
     G=9.0 / 52.0,
     q_pos=0.14,