diff --git a/src/ground_vehicle.hpp b/src/ground_vehicle.hpp
index d71eb73345..5033bef752 100644
--- a/src/ground_vehicle.hpp
+++ b/src/ground_vehicle.hpp
@@ -22,20 +22,20 @@ enum AccelStatus {
 };
 
 /**
- * Cached values.
+ * Cached, frequently calculated values.
  * All of these values except cached_slope_resistance are set only for the first part of a vehicle.
  */
 struct GroundVehicleCache {
 	/* Cached acceleration values, recalculated when the cargo on a vehicle changes (in addition to the conditions below) */
-	uint32 cached_weight;           ///< Total weight of the consist.
+	uint32 cached_weight;           ///< Total weight of the consist (valid only for the first engine).
 	uint32 cached_slope_resistance; ///< Resistance caused by weight when this vehicle part is at a slope.
-	uint32 cached_max_te;           ///< Maximum tractive effort of consist.
-	uint16 cached_axle_resistance;  ///< Resistance caused by the axles of the vehicle.
+	uint32 cached_max_te;           ///< Maximum tractive effort of consist (valid only for the first engine).
+	uint16 cached_axle_resistance;  ///< Resistance caused by the axles of the vehicle (valid only for the first engine).
 
 	/* Cached acceleration values, recalculated on load and each time a vehicle is added to/removed from the consist. */
-	uint16 cached_max_track_speed;  ///< Maximum consist speed limited by track type.
-	uint32 cached_power;            ///< Total power of the consist.
-	uint32 cached_air_drag;         ///< Air drag coefficient of the vehicle.
+	uint16 cached_max_track_speed;  ///< Maximum consist speed limited by track type (valid only for the first engine).
+	uint32 cached_power;            ///< Total power of the consist (valid only for the first engine).
+	uint32 cached_air_drag;         ///< Air drag coefficient of the vehicle (valid only for the first engine).
 };
 
 /** Ground vehicle flags. */