Index: binaries/data/mods/public/simulation/components/Formation.js
===================================================================
--- binaries/data/mods/public/simulation/components/Formation.js
+++ binaries/data/mods/public/simulation/components/Formation.js
@@ -903,21 +903,32 @@
 {
 	let minSpeed = Infinity;
 	let minAcceleration = Infinity;
+	let maxClearance = 0;
+	let maxPassClass;
 
+	const cmpPathfinder = Engine.QueryInterface(SYSTEM_ENTITY, IID_Pathfinder);
 	for (let ent of this.members)
 	{
-		let cmpUnitMotion = Engine.QueryInterface(ent, IID_UnitMotion);
-		if (cmpUnitMotion)
+		const cmpUnitMotion = Engine.QueryInterface(ent, IID_UnitMotion);
+		if (!cmpUnitMotion)
+			continue;
+		minSpeed = Math.min(minSpeed, cmpUnitMotion.GetWalkSpeed());
+		minAcceleration = Math.min(minAcceleration, cmpUnitMotion.GetAcceleration());
+
+		const passClass = cmpUnitMotion.GetPassabilityClassName();
+		const clearance = cmpPathfinder.GetClearance(cmpPathfinder.GetPassabilityClass(passClass));
+		if (clearance > maxClearance)
 		{
-			minSpeed = Math.min(minSpeed, cmpUnitMotion.GetWalkSpeed());
-			minAcceleration = Math.min(minAcceleration, cmpUnitMotion.GetAcceleration());
+			maxClearance = clearance;
+			maxPassClass = passClass;
 		}
 	}
 	minSpeed *= this.GetSpeedMultiplier();
 
-	let cmpUnitMotion = Engine.QueryInterface(this.entity, IID_UnitMotion);
+	const cmpUnitMotion = Engine.QueryInterface(this.entity, IID_UnitMotion);
 	cmpUnitMotion.SetSpeedMultiplier(minSpeed / cmpUnitMotion.GetWalkSpeed());
 	cmpUnitMotion.SetAcceleration(minAcceleration);
+	cmpUnitMotion.SetPassabilityClassName(maxPassClass);
 };
 
 Formation.prototype.ShapeUpdate = function()
Index: binaries/data/mods/public/simulation/components/tests/test_UnitAI.js
===================================================================
--- binaries/data/mods/public/simulation/components/tests/test_UnitAI.js
+++ binaries/data/mods/public/simulation/components/tests/test_UnitAI.js
@@ -247,12 +247,18 @@
 		"StopMoving": () => {},
 		"SetSpeedMultiplier": () => {},
 		"SetAcceleration": (accel) => {},
+		"SetPassabilityClassName": (name) => {},
 		"MoveToPointRange": () => true,
 		"SetFacePointAfterMove": () => {},
 		"GetFacePointAfterMove": () => true,
 		"GetPassabilityClassName": () => "default"
 	});
 
+	AddMock(SYSTEM_ENTITY, IID_Pathfinder, {
+		"GetClearance": () => 1,
+		"GetPassabilityClass": () => 16
+	});
+
 	controllerAI.OnCreate();
 
 
@@ -420,6 +426,7 @@
 		"GetWalkSpeed": () => 1,
 		"SetSpeedMultiplier": (speed) => {},
 		"SetAcceleration": (accel) => {},
+		"SetPassabilityClassName": (name) => {},
 		"MoveToPointRange": (x, z, minRange, maxRange) => {},
 		"StopMoving": () => {},
 		"SetFacePointAfterMove": () => {},
@@ -427,6 +434,11 @@
 		"GetPassabilityClassName": () => "default"
 	});
 
+	AddMock(SYSTEM_ENTITY, IID_Pathfinder, {
+		"GetClearance": () => 1,
+		"GetPassabilityClass": () => 16
+	});
+
 	AddMock(controller, IID_Attack, {
 		"GetRange": function() { return { "max": 10, "min": 0 }; },
 		"CanAttackAsFormation": function() { return false; },
Index: source/simulation2/components/ICmpPathfinder.cpp
===================================================================
--- source/simulation2/components/ICmpPathfinder.cpp
+++ source/simulation2/components/ICmpPathfinder.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -24,6 +24,7 @@
 BEGIN_INTERFACE_WRAPPER(Pathfinder)
 DEFINE_INTERFACE_METHOD("SetDebugOverlay", ICmpPathfinder, SetDebugOverlay)
 DEFINE_INTERFACE_METHOD("SetHierDebugOverlay", ICmpPathfinder, SetHierDebugOverlay)
+DEFINE_INTERFACE_METHOD("GetClearance", ICmpPathfinder, GetClearance)
 DEFINE_INTERFACE_METHOD("GetPassabilityClass", ICmpPathfinder, GetPassabilityClass)
 DEFINE_INTERFACE_METHOD("UpdateGrid", ICmpPathfinder, UpdateGrid)
 END_INTERFACE_WRAPPER(Pathfinder)