diff --git a/selfdrive/car/card.py b/selfdrive/car/card.py
index 25ca105427..cd8740dd5c 100755
--- a/selfdrive/car/card.py
+++ b/selfdrive/car/card.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+import dataclasses
 import os
 import time
 
@@ -58,8 +59,24 @@ def can_comm_callbacks(logcan: messaging.SubSocket, sendcan: messaging.PubSocket
   return can_recv, can_send
 
 
+def convert_to_capnp(CP: CarParams) -> car.CarParams:
+  CP_dict = dataclasses.asdict(CP)
+  del CP_dict['lateralTuning']
+  CP_capnp = car.CarParams.new_message(**CP_dict)
+
+  # this is the only union, special handling
+  which = CP.lateralTuning.which()
+  CP_capnp.lateralTuning.init(which)
+  lateralTuning_dict = dataclasses.asdict(getattr(CP.lateralTuning, which))
+  setattr(CP_capnp.lateralTuning, which, lateralTuning_dict)
+
+  return CP_capnp
+
+
 class Car:
   CI: CarInterfaceBase
+  CP: CarParams
+  CP_capnp: car.CarParams
 
   def __init__(self, CI=None) -> None:
     self.can_sock = messaging.sub_sock('can', timeout=20)
@@ -126,7 +143,9 @@ class Car:
       self.params.put("CarParamsPrevRoute", prev_cp)
 
     # Write CarParams for controls and radard
-    cp_bytes = self.CP.to_bytes()
+    # convert to pycapnp representation for caching and logging
+    self.CP_capnp = convert_to_capnp(self.CP)
+    cp_bytes = self.CP_capnp.to_bytes()
     self.params.put("CarParams", cp_bytes)
     self.params.put_nonblocking("CarParamsCache", cp_bytes)
     self.params.put_nonblocking("CarParamsPersistent", cp_bytes)
@@ -176,7 +195,7 @@ class Car:
     if self.sm.frame % int(50. / DT_CTRL) == 0:
       cp_send = messaging.new_message('carParams')
       cp_send.valid = True
-      cp_send.carParams = self.CP
+      cp_send.carParams = self.CP_capnp
       self.pm.send('carParams', cp_send)
 
     # publish new carOutput