--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -477,9 +477,7 @@
 	/* Recalculate */
 	Group *g;
 	FOR_ALL_GROUPS(g) {
-		g->num_vehicle = 0;
-		free(g->num_engines);
-		g->num_engines = CallocT<EngineID>(engines);
+		g->statistics.Clear();
 	}
 
 	const Vehicle *v;
@@ -496,8 +494,8 @@
 		assert(v->type == g->vehicle_type);
 		assert(v->owner == g->owner);
 
-		g->num_engines[v->engine_type]++;
-		if (v->IsPrimaryVehicle()) g->num_vehicle++;
+		g->statistics.num_engines[v->engine_type]++;
+		if (v->IsPrimaryVehicle()) g->statistics.num_vehicle++;
 	}
 }
 

--- a/src/group.h
+++ b/src/group.h
@@ -21,16 +21,25 @@
 typedef Pool<Group, GroupID, 16, 64000> GroupPool;
 extern GroupPool _group_pool; ///< Pool of groups.
 
+/** Statistics and caches on the vehicles in a group. */
+struct GroupStatistics {
+	uint16 num_vehicle;                     ///< Number of vehicles.
+	uint16 *num_engines;                    ///< Caches the number of engines of each type the company owns.
+
+	GroupStatistics();
+	~GroupStatistics();
+
+	void Clear();
+};
+
 /** Group data. */
 struct Group : GroupPool::PoolItem<&_group_pool> {
 	char *name;                             ///< Group Name
-
-	uint16 num_vehicle;                     ///< Number of vehicles in the group
 	OwnerByte owner;                        ///< Group Owner
 	VehicleTypeByte vehicle_type;           ///< Vehicle type of the group
 
 	bool replace_protection;                ///< If set to true, the global autoreplace have no effect on the group
-	uint16 *num_engines;                    ///< Caches the number of engines of each type the company owns (no need to save this)
+	GroupStatistics statistics;             ///< NOSAVE: Statistics and caches on the vehicles in the group.
 
 	Group(CompanyID owner = INVALID_COMPANY);
 	~Group();
@@ -77,7 +86,7 @@
 static inline void IncreaseGroupNumVehicle(GroupID id_g)
 {
 	Group *g = Group::GetIfValid(id_g);
-	if (g != NULL) g->num_vehicle++;
+	if (g != NULL) g->statistics.num_vehicle++;
 }
 
 /**
@@ -87,7 +96,7 @@
 static inline void DecreaseGroupNumVehicle(GroupID id_g)
 {
 	Group *g = Group::GetIfValid(id_g);
-	if (g != NULL) g->num_vehicle--;
+	if (g != NULL) g->statistics.num_vehicle--;
 }
 
 

--- a/src/group_cmd.cpp
+++ b/src/group_cmd.cpp
@@ -32,6 +32,29 @@
 GroupPool _group_pool("Group");
 INSTANTIATE_POOL_METHODS(Group)
 
+GroupStatistics::GroupStatistics()
+{
+	this->num_engines = CallocT<uint16>(Engine::GetPoolSize());
+}
+
+GroupStatistics::~GroupStatistics()
+{
+	free(this->num_engines);
+}
+
+/**
+ * Clear all caches.
+ */
+void GroupStatistics::Clear()
+{
+	this->num_vehicle = 0;
+
+	/* This is also called when NewGRF change. So the number of engines might have changed. Reallocate. */
+	free(this->num_engines);
+	this->num_engines = CallocT<uint16>(Engine::GetPoolSize());
+}
+
+
 /**
  * Update the num engines of a groupID. Decrease the old one and increase the new one
  * @note called in SetTrainGroupID and UpdateTrainGroupID
@@ -43,10 +66,10 @@
 {
 	if (old_g != new_g) {
 		/* Decrease the num engines of EngineID i of the old group if it's not the default one */
-		if (!IsDefaultGroupID(old_g) && Group::IsValidID(old_g)) Group::Get(old_g)->num_engines[i]--;
+		if (!IsDefaultGroupID(old_g) && Group::IsValidID(old_g)) Group::Get(old_g)->statistics.num_engines[i]--;
 
 		/* Increase the num engines of EngineID i of the new group if it's not the default one */
-		if (!IsDefaultGroupID(new_g) && Group::IsValidID(new_g)) Group::Get(new_g)->num_engines[i]++;
+		if (!IsDefaultGroupID(new_g) && Group::IsValidID(new_g)) Group::Get(new_g)->statistics.num_engines[i]++;
 	}
 }
 
@@ -55,16 +78,11 @@
 Group::Group(Owner owner)
 {
 	this->owner = owner;
-
-	if (!Company::IsValidID(owner)) return;
-
-	this->num_engines = CallocT<uint16>(Engine::GetPoolSize());
 }
 
 Group::~Group()
 {
 	free(this->name);
-	free(this->num_engines);
 }
 
 
@@ -414,14 +432,14 @@
  */
 uint GetGroupNumEngines(CompanyID company, GroupID id_g, EngineID id_e)
 {
-	if (Group::IsValidID(id_g)) return Group::Get(id_g)->num_engines[id_e];
+	if (Group::IsValidID(id_g)) return Group::Get(id_g)->statistics.num_engines[id_e];
 
 	uint num = Company::Get(company)->num_engines[id_e];
 	if (!IsDefaultGroupID(id_g)) return num;
 
 	const Group *g;
 	FOR_ALL_GROUPS(g) {
-		if (g->owner == company) num -= g->num_engines[id_e];
+		if (g->owner == company) num -= g->statistics.num_engines[id_e];
 	}
 	return num;
 }

--- a/src/group_gui.cpp
+++ b/src/group_gui.cpp
@@ -303,8 +303,8 @@
 
 					SetDParam(0, STR_GROUP_NAME);
 					SetDParam(1, g->index);
-					SetDParam(2, g->num_vehicle);
-					SetDParam(3, g->num_vehicle);
+					SetDParam(2, g->statistics.num_vehicle);
+					SetDParam(3, g->statistics.num_vehicle);
 				}
 				break;
 		}
@@ -391,7 +391,7 @@
 					DrawString(r.left + WD_FRAMERECT_LEFT + 8, r.right - WD_FRAMERECT_RIGHT - 8, y1, STR_GROUP_NAME, (this->vli.index == g->index) ? TC_WHITE : TC_BLACK);
 
 					/* draw the number of vehicles of the group */
-					SetDParam(0, g->num_vehicle);
+					SetDParam(0, g->statistics.num_vehicle);
 					DrawString(r.left + WD_FRAMERECT_LEFT, r.right - WD_FRAMERECT_RIGHT, y1 + 1, STR_TINY_COMMA, (this->vli.index == g->index) ? TC_WHITE : TC_BLACK, SA_RIGHT);
 
 					y1 += this->tiny_step_height;

--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -697,7 +697,7 @@
 		if (this->owner == _local_company) InvalidateAutoreplaceWindow(this->engine_type, this->group_id);
 
 		DeleteGroupHighlightOfVehicle(this);
-		if (Group::IsValidID(this->group_id)) Group::Get(this->group_id)->num_engines[this->engine_type]--;
+		if (Group::IsValidID(this->group_id)) Group::Get(this->group_id)->statistics.num_engines[this->engine_type]--;
 		if (this->IsPrimaryVehicle()) DecreaseGroupNumVehicle(this->group_id);
 	}