diff --git a/source/main/gui/GUIUtils.cpp b/source/main/gui/GUIUtils.cpp
index be595a539a..1cbdb80dcd 100644
--- a/source/main/gui/GUIUtils.cpp
+++ b/source/main/gui/GUIUtils.cpp
@@ -440,34 +440,31 @@ void RoR::ImDrawModifierKeyHighlighted(OIS::KeyCode key)
 bool RoR::ImButtonHoldToConfirm(const std::string& btn_caption, bool small, float time_limit, float& time_left_var, float dt)
 {
 
-    bool btn_pressed = false;
     if (small)
-        btn_pressed = ImGui::SmallButton(btn_caption.c_str());
+        ImGui::SmallButton(btn_caption.c_str());
     else
-        btn_pressed = ImGui::Button(btn_caption.c_str());
+        ImGui::Button(btn_caption.c_str());
 
-    if (btn_pressed)
+    if (ImGui::IsItemActive() && time_left_var > 0.f)
     {
-        time_left_var = time_limit; // Initialize
+        time_left_var -= dt;
+        if (time_left_var > 0.f)
+        {
+            ImGui::BeginTooltip();
+            std::string text = _L("Hold to confirm");
+            ImGui::TextDisabled(text.c_str());
+            ImGui::ProgressBar(time_left_var/time_limit, ImVec2(ImGui::CalcTextSize(text.c_str()).x, 8.f), "");
+            ImGui::EndTooltip();
+        }
+        else
+        {
+            return true;
+        }
     }
     else
     {
-        if (ImGui::IsItemActive() && time_left_var > 0.f)
-        {
-            time_left_var -= dt;
-            if (time_left_var > 0.f)
-            {
-                ImGui::BeginTooltip();
-                std::string text = _L("Hold to confirm");
-                ImGui::TextDisabled(text.c_str());
-                ImGui::ProgressBar(time_left_var/time_limit, ImVec2(ImGui::CalcTextSize(text.c_str()).x, 8.f), "");
-                ImGui::EndTooltip();
-            }
-            else
-            {
-                return true;
-            }
-        }
+        time_left_var = time_limit;
     }
+
     return false;
 }
diff --git a/source/main/gui/panels/GUI_TopMenubar.cpp b/source/main/gui/panels/GUI_TopMenubar.cpp
index 2e16eec831..ec64e5ab0e 100644
--- a/source/main/gui/panels/GUI_TopMenubar.cpp
+++ b/source/main/gui/panels/GUI_TopMenubar.cpp
@@ -1594,13 +1594,13 @@ void TopMenubar::Draw(float dt)
 
                 ImGui::SetNextItemOpen(true, ImGuiCond_FirstUseEver);
                 std::string addonparts_title = fmt::format(_LC("TopMenubar", "Addon parts ({})"), tuning_addonparts.cqy_results.size());
-                if (ImGui::CollapsingHeader(addonparts_title.c_str()))
+                if (ImGui::CollapsingHeader(addonparts_title.c_str()) && tuneup_entry)
                 {
                     for (CacheQueryResult& addonpart_result: tuning_addonparts.cqy_results)
                     {
                         ImGui::PushID(addonpart_result.cqr_entry->fname.c_str());
 
-                        bool used = tuning_actor->getUsedTuneupEntry()->tuneup_def->use_addonparts.count(addonpart_result.cqr_entry->fname) > 0;
+                        bool used = tuneup_entry->tuneup_def->use_addonparts.count(addonpart_result.cqr_entry->fname) > 0;
                         if (ImGui::Checkbox(addonpart_result.cqr_entry->dname.c_str(), &used))
                         {
                             ModifyProjectRequest* req = new ModifyProjectRequest();
diff --git a/source/main/physics/flex/FlexBody.cpp b/source/main/physics/flex/FlexBody.cpp
index 9a62b6f85f..d52d0ffca9 100644
--- a/source/main/physics/flex/FlexBody.cpp
+++ b/source/main/physics/flex/FlexBody.cpp
@@ -573,7 +573,9 @@ void FlexBody::setVisible(bool visible)
 
 void FlexBody::setFlexbodyCastShadow(bool val)
 {
-    m_scene_entity->setCastShadows(val);
+    // Scene entity is NULL if disabled via addonpart/tuneup.
+    if (m_scene_entity)
+        m_scene_entity->setCastShadows(val);
 }
 
 void FlexBody::computeFlexbody()
diff --git a/source/main/resources/CacheSystem.cpp b/source/main/resources/CacheSystem.cpp
index 9852a72bc4..e5e82e456b 100644
--- a/source/main/resources/CacheSystem.cpp
+++ b/source/main/resources/CacheSystem.cpp
@@ -1351,8 +1351,12 @@ void CacheSystem::UnLoadResource(CacheEntryPtr& entry)
     {
         if (i_entry->resource_group == resource_group)
         {
-            i_entry->actor_def = nullptr; // Delete cached truck file - force reload from disk
-            i_entry->resource_group = ""; // Mark as unloaded
+            // Delete cached documents - force reload from disk
+            i_entry->actor_def = nullptr;
+            i_entry->tuneup_def = nullptr;
+            i_entry->skin_def = nullptr;
+            // Mark as unloaded
+            i_entry->resource_group = "";
         }
     }
 
diff --git a/source/main/resources/addonpart_fileformat/AddonPartFileFormat.cpp b/source/main/resources/addonpart_fileformat/AddonPartFileFormat.cpp
index e744175d65..442747cd6e 100644
--- a/source/main/resources/addonpart_fileformat/AddonPartFileFormat.cpp
+++ b/source/main/resources/addonpart_fileformat/AddonPartFileFormat.cpp
@@ -116,6 +116,12 @@ void AddonPartUtility::ResolveUnwantedAndTweakedElements(TuneupDefPtr& tuneup, C
     m_addonpart_entry = addonpart_entry;
     m_tuneup = tuneup;
 
+    // Reset tweak data - to be reloaded from addonpart
+    m_tuneup->prop_tweaks.clear();
+    m_tuneup->flexbody_tweaks.clear();
+    m_tuneup->wheel_tweaks.clear();
+    m_tuneup->node_tweaks.clear();
+
     try
     {
         Ogre::DataStreamPtr datastream = Ogre::ResourceGroupManager::getSingleton().openResource(addonpart_entry->fname, addonpart_entry->resource_group);
diff --git a/source/main/resources/tuneup_fileformat/TuneupFileFormat.cpp b/source/main/resources/tuneup_fileformat/TuneupFileFormat.cpp
index 7e3d4faca1..6cce39b90a 100644
--- a/source/main/resources/tuneup_fileformat/TuneupFileFormat.cpp
+++ b/source/main/resources/tuneup_fileformat/TuneupFileFormat.cpp
@@ -412,6 +412,7 @@ void RoR::TuneupUtil::ParseTuneupAttribute(const std::string& line, TuneupDefPtr
     if (attrib == "remove_flexbody" && params.size() == 2) { tuneup_def->remove_flexbodies.insert(PARSEINT(params[1])); return; }
     if (attrib == "protected_prop"     && params.size() == 2) { tuneup_def->protected_props.insert(PARSEINT(params[1])); return; }
     if (attrib == "protected_flexbody" && params.size() == 2) { tuneup_def->protected_flexbodies.insert(PARSEINT(params[1])); return; }
+    if (attrib == "forced_wheel_side" && params.size() == 3) { tuneup_def->wheel_forced_sides[PARSEINT(params[1])] = (WheelSide)PARSEINT(params[2]); return; }
 }
 
 void RoR::TuneupUtil::ExportTuneup(Ogre::DataStreamPtr& stream, TuneupDefPtr& tuneup)
@@ -450,6 +451,10 @@ void RoR::TuneupUtil::ExportTuneup(Ogre::DataStreamPtr& stream, TuneupDefPtr& tu
     {
         buf << "\tprotected_flexbody = " << (int)protected_flexbody << "\n";
     }
+    for (auto& pair: tuneup->wheel_forced_sides)
+    {
+        buf << "\tforced_wheel_side = " << pair.first << ", " << (int)pair.second << "\n";
+    }
     buf << "}\n\n";
 
     size_t written = stream->write(buf.GetBuffer(), buf.GetLength());
diff --git a/source/main/resources/tuneup_fileformat/TuneupFileFormat.h b/source/main/resources/tuneup_fileformat/TuneupFileFormat.h
index 2a9f774fab..c4c39c9227 100644
--- a/source/main/resources/tuneup_fileformat/TuneupFileFormat.h
+++ b/source/main/resources/tuneup_fileformat/TuneupFileFormat.h
@@ -91,8 +91,8 @@ struct TuneupDef: public RefCountingObject<TuneupDef>
 
     std::map<NodeNum_t, TuneupNodeTweak>          node_tweaks;           //!< Node position overrides via 'addonpart_tweak_node'
     std::map<WheelID_t, TuneupWheelTweak>         wheel_tweaks;          //!< Mesh name and radius overrides via 'addonpart_tweak_wheel'
-    std::map<PropID_t, TuneupPropTweak>           prop_tweaks;
-    std::map<FlexbodyID_t, TuneupFlexbodyTweak>   flexbody_tweaks;
+    std::map<PropID_t, TuneupPropTweak>           prop_tweaks;           //!< Mesh name(s), offset and rotation overrides via 'addonpart_tweak_prop'
+    std::map<FlexbodyID_t, TuneupFlexbodyTweak>   flexbody_tweaks;       //!< Mesh name, offset and rotation overrides via 'addonpart_tweak_flexbody'
 
     std::set<PropID_t>                            remove_props;          //!< Either UI overrides or 'addonpart_unwanted_prop' directives.
     std::set<FlexbodyID_t>                        remove_flexbodies;     //!< Either UI overrides or 'addonpart_unwanted_flexbody' directives.