diff --git a/docs/BUILD.md b/docs/BUILD.md
index ff9177a..b97df58 100644
--- a/docs/BUILD.md
+++ b/docs/BUILD.md
@@ -38,7 +38,7 @@ node --version  # v18+ required
    ```bash
    cp secrets.ini.example secrets.ini
    ```
-   Edit `secrets.ini` with your WiFi SSID and password. Optionally change the mDNS hostname (default: `ztrain`) and `MAX_PWM` to tune top speed (default: `500` — about half voltage to the track, which is plenty for Z-scale). These are plain PlatformIO `build_flags` (`-D WIFI_SSID='"..."'` etc. — note the single-quote wrapping, required so values with spaces survive PlatformIO's flag tokenizer) merged in via `extra_configs` in `platformio.ini` — `secrets.ini` is gitignored, so nothing here ever gets committed.
+   Edit `secrets.ini` with your WiFi SSID and password. Optionally change the mDNS hostname (default: `ztrain`), `MAX_PWM` to tune top speed (default: `1000` — full voltage to the track), and `PWM_FREQ` to tune the motor's PWM switching frequency in Hz (default: `20000` — above the audible range, so the motor doesn't whine). `analogWrite` on the ESP8266 is software PWM sharing one hardware timer across all 4 active channels (motor + R/G/B status LED), so pushing `PWM_FREQ` too high risks starving the WiFi/WebSocket stack — the build fails outright above `40000` as a safety ceiling. These are plain PlatformIO `build_flags` (`-D WIFI_SSID='"..."'` etc. — note the single-quote wrapping, required so values with spaces survive PlatformIO's flag tokenizer) merged in via `extra_configs` in `platformio.ini` — `secrets.ini` is gitignored, so nothing here ever gets committed.
 
 3. **Install frontend dependencies:**
    ```bash
diff --git a/firmware/z-duino/z-duino.ino b/firmware/z-duino/z-duino.ino
index 59c5b1a..9f85c1b 100644
--- a/firmware/z-duino/z-duino.ino
+++ b/firmware/z-duino/z-duino.ino
@@ -11,7 +11,15 @@
 #include <MotorLogic.h>
 #include <Command.h>
 
-#define VERSION "2.3.0"
+#define VERSION "2.4.0"
+
+// analogWrite on ESP8266 is software PWM sharing one hardware timer across
+// all 4 active channels (motor + R/G/B status LED). Above ~40kHz the
+// interrupt load starts contending with the WiFi/WebSocket stack, risking
+// jitter and dropped connections.
+#if PWM_FREQ > 40000
+#error "PWM_FREQ exceeds the 40kHz safe ceiling for this board's shared software-PWM timer"
+#endif
 
 // WiFi credentials from secrets.ini
 char wifi_ssid[] = WIFI_SSID;
@@ -186,8 +194,8 @@ void setup() {
   pinMode(stby, OUTPUT);
   digitalWrite(stby, HIGH);
 
-  // PWM config: 20kHz (above audible range), 0-1000 range
-  analogWriteFreq(20000);
+  // PWM config: frequency from secrets.ini (above audible range), 0-1000 range
+  analogWriteFreq(PWM_FREQ);
   analogWriteRange(1000);
 
   // Initialize LittleFS
diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index 28ea4e0..20a9b5f 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "z-duino-frontend",
-  "version": "2.3.0",
+  "version": "2.4.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "z-duino-frontend",
-      "version": "2.3.0",
+      "version": "2.4.0",
       "dependencies": {
         "@nuxt/ui": "^4.5.1",
         "tailwindcss": "^4.2.1",
diff --git a/frontend/package.json b/frontend/package.json
index 2000aa0..c5ee93a 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -1,6 +1,6 @@
 {
   "name": "z-duino-frontend",
-  "version": "2.3.0",
+  "version": "2.4.0",
   "private": true,
   "type": "module",
   "scripts": {
diff --git a/frontend/src/components/DebugModal.vue b/frontend/src/components/DebugModal.vue
index 0df4d69..6c87358 100644
--- a/frontend/src/components/DebugModal.vue
+++ b/frontend/src/components/DebugModal.vue
@@ -19,7 +19,7 @@
             :class="i % 2 === 0 ? 'bg-neutral-800/50' : ''"
           >
             <td class="px-3 py-1.5 font-medium text-neutral-400 whitespace-nowrap">{{ row.label }}</td>
-            <td class="px-3 py-1.5 text-white break-all">{{ row.value }}</td>
+            <td class="px-3 py-1.5 break-all" :class="row.danger ? 'font-bold text-red-500' : 'text-white'">{{ row.value }}</td>
           </tr>
         </tbody>
       </table>
@@ -34,7 +34,7 @@ import { useTrainController } from '../composables/useTrainController'
 const { getDebugInfo } = useTrainController()
 
 const isOpen = ref(false)
-const rows = ref<{ label: string; value: string }[]>([])
+const rows = ref<{ label: string; value: string; danger?: boolean }[]>([])
 
 function open() {
   rows.value = getDebugInfo()
diff --git a/frontend/src/components/SpeedController.vue b/frontend/src/components/SpeedController.vue
index c66d92c..06ab812 100644
--- a/frontend/src/components/SpeedController.vue
+++ b/frontend/src/components/SpeedController.vue
@@ -4,7 +4,7 @@
     <div class="mb-3">
       <div class="flex justify-between text-sm text-neutral-400 mb-1">
         <span><span class="font-bold">Speed:</span> {{ currentSpeed === 0 ? 'stopped' : Math.round(currentSpeed * 100) + '%' }}</span>
-        <span><span class="font-bold">Track:</span> {{ (12 * currentSpeed).toFixed(1) }}V</span>
+        <span :class="trackVoltageDanger ? 'font-bold text-red-500' : ''"><span class="font-bold">Track:</span> {{ trackVoltage.toFixed(1) }}V</span>
       </div>
       <div class="flex w-full">
         <button
@@ -61,6 +61,8 @@ const {
   connected,
   currentSpeed,
   currentDirection,
+  trackVoltage,
+  trackVoltageDanger,
   getSegmentClass,
   setSpeed,
   toggleDirection,
diff --git a/frontend/src/composables/useTrainController.ts b/frontend/src/composables/useTrainController.ts
index bdc4570..2129aca 100644
--- a/frontend/src/composables/useTrainController.ts
+++ b/frontend/src/composables/useTrainController.ts
@@ -1,4 +1,4 @@
-import { ref } from 'vue'
+import { computed, ref } from 'vue'
 
 // WebSocket protocol types
 interface OutgoingSpeed { cmd: 'speed'; value: number }
@@ -48,6 +48,8 @@ const DIRECTION_PAUSE = 500
 const RECONNECT_BASE = 1000
 const RECONNECT_MAX = 30000
 const PING_INTERVAL = 10000
+const SUPPLY_VOLTAGE = 12
+const TRACK_VOLTAGE_DANGER_THRESHOLD = 10
 
 export const powerLevels = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0]
 
@@ -76,6 +78,9 @@ const ledBright = ref(true)
 const activeLedColor = ref<string | null>(null)
 const partyMode = ref(false)
 
+const trackVoltage = computed(() => SUPPLY_VOLTAGE * currentSpeed.value)
+const trackVoltageDanger = computed(() => trackVoltage.value > TRACK_VOLTAGE_DANGER_THRESHOLD)
+
 let rampTimer: ReturnType<typeof setInterval> | null = null
 let partyTimer: ReturnType<typeof setTimeout> | null = null
 let reconnectDelay = RECONNECT_BASE
@@ -347,7 +352,7 @@ function togglePartyMode() {
 
 const WS_READY_STATES = ['CONNECTING', 'OPEN', 'CLOSING', 'CLOSED'] as const
 
-function getDebugInfo(): { label: string; value: string }[] {
+function getDebugInfo(): { label: string; value: string; danger?: boolean }[] {
   const wsUrl = socket.value ? socket.value.url : `ws://${location.hostname || 'localhost'}:81/`
   const wsState = socket.value ? WS_READY_STATES[socket.value.readyState] : 'N/A'
 
@@ -359,8 +364,8 @@ function getDebugInfo(): { label: string; value: string }[] {
     { label: 'WebSocket State', value: wsState },
     { label: 'Reconnect Delay', value: `${reconnectDelay}ms` },
     { label: 'Current Speed', value: currentSpeed.value === 0 ? 'stopped' : `${Math.round(currentSpeed.value * 100)}%` },
-    { label: 'Supply Voltage', value: '12V' },
-    { label: 'Track Voltage', value: `${(12 * currentSpeed.value).toFixed(1)}V` },
+    { label: 'Supply Voltage', value: `${SUPPLY_VOLTAGE}V` },
+    { label: 'Track Voltage', value: `${trackVoltage.value.toFixed(1)}V`, danger: trackVoltageDanger.value },
     { label: 'Direction', value: currentDirection.value ? 'FWD' : 'REV' },
     { label: 'Direction Inverted', value: String(directionInverted.value) },
     { label: 'Ramping', value: String(rampTimer !== null) },
@@ -390,6 +395,8 @@ export function useTrainController() {
     currentSpeed,
     currentDirection,
     directionInverted,
+    trackVoltage,
+    trackVoltageDanger,
     ledTestMode,
     ledBright,
     activeLedColor,
diff --git a/secrets.ini.example b/secrets.ini.example
index 54988f5..1bcebf5 100644
--- a/secrets.ini.example
+++ b/secrets.ini.example
@@ -10,4 +10,5 @@ build_flags =
     -D WIFI_PASS='"YourPasswordHere"'
     -D MDNS_HOSTNAME='"ztrain"'
     -D RAILROAD_NAME='"Z-Duino"'
-    -D MAX_PWM=500
+    -D MAX_PWM=1000
+    -D PWM_FREQ=20000