diff --git a/docs/mobile-app.md b/docs/mobile-app.md
index a6aefe7..9d35e0c 100644
--- a/docs/mobile-app.md
+++ b/docs/mobile-app.md
@@ -673,6 +673,7 @@ CREATE TABLE settings (
 | `api_token` | Bearer token for API auth (obtained via Connect, never stored in plaintext long-term) | Both |
 | `sync_mode` | `"summaries"` (default) or `"full"` — controls whether geojson+timeseries are downloaded during sync | Both |
 | `sync_upload` | `"true"` or `"false"` — whether to push local activities during sync | Both |
+| `upload_format` | `"raw"` (default) or `"bas"` — whether to upload the original FIT/GPX/TCX file (server re-extracts with DEM) or the pre-extracted JSON | Both |
 | `auto_import_path` | Directory to watch for new FIT files | **Android only** |
 
 ---
@@ -700,17 +701,18 @@ Implemented in `mobile/db/sync.ts` → `uploadFeed()` / `uploadLocalActivities()
 
 1. **Reconcile** against the server: fetch `GET /api/feed` and compare its activity IDs against local rows where `synced_at IS NOT NULL`. Any local activity that is marked as synced but absent from the server (e.g. server was wiped) has its `synced_at` cleared so it re-enters the upload queue. This is best-effort — if the feed fetch fails, upload proceeds with whatever is currently queued.
 2. Query `activities WHERE origin = 'local' AND synced_at IS NULL`.
-3. For each: parse `detail_json` from the DB row and construct `{ id: row.id, ...detail }`.
-4. `POST {instance_url}/api/upload/bas` with body `{ activity, timeseries?, geojson? }`.
-5. On 200 (including `{ status: "duplicate" }`): set `synced_at = unixepoch()`. On error: log to console, count as failed, continue with the next activity.
+3. For each, choose the upload path based on the `upload_format` setting (default `'raw'`):
+   - **`raw` (default):** if `original_path` is set and the file still exists on disk, read it as base64 and `POST {instance_url}/api/upload/raw { filename, base64 }`. The server re-extracts the file with DEM elevation correction and returns `{ id, detail, timeseries, geojson, source_hash }`. After a successful upload, the local row's `detail_json`, `timeseries_json`, `geojson`, and `source_hash` are updated with the server's better data (Option A). Falls back to `bas` if the file is missing.
+   - **`bas`:** `POST {instance_url}/api/upload/bas { activity, timeseries?, geojson? }` with the pre-extracted JSON from the DB. Faster, but no DEM elevation correction.
+4. On 200 (including `{ status: "duplicate" }`): set `synced_at = unixepoch()`. On error: log to console, count as failed, continue with next activity.
 
 The UI shows live progress ("Uploading N / M…") during the batch and reports failures separately ("X uploaded, Y failed").
 
-The server endpoint (`bincio/serve/server.py` → `POST /api/upload/bas`) accepts
-pre-extracted BAS JSON rather than raw FIT/GPX/TCX. It writes the activity file,
-**updates `user_dir/index.json`** with a summary entry (so `merge_all` can include
-the activity in year shards and the browser feed), writes geojson and timeseries if
-provided, then calls `merge_all()` + `write_combined_feed()`.
+**Upload format setting (`upload_format`):** controls whether to prefer the original raw file or the pre-extracted JSON. `raw` is the default and is recommended — it produces DEM-corrected elevation data on the server and back-fills the local copy. Switching between modes is safe: the server deduplicates by activity id, so switching from `raw` to `bas` just results in the server returning `{ status: "duplicate" }` (HTTP 200) and the client marking the activity as synced.
+
+**Server endpoint for BAS JSON** (`POST /api/upload/bas`): accepts pre-extracted BAS JSON, writes the activity file, updates `user_dir/index.json` with a summary entry (so `merge_all` can include the activity in year shards and the browser feed), writes geojson and timeseries if provided, then calls `merge_all()` + `write_combined_feed()`.
+
+**Server endpoint for raw files** (`POST /api/upload/raw`): accepts a base64-encoded FIT/GPX/TCX file, runs full server-side extraction with DEM correction, stores the result, updates the index, calls `merge_all()` + `write_combined_feed()`, and returns the full extracted data to the client.
 
 > **Bug that was fixed:** earlier versions of both `/api/upload/bas` and `/api/upload/raw`
 > wrote activity files to disk but never updated `user_dir/index.json`. Since `merge_all`
diff --git a/mobile/app/(tabs)/settings.tsx b/mobile/app/(tabs)/settings.tsx
index 1d08085..c38d4d7 100644
--- a/mobile/app/(tabs)/settings.tsx
+++ b/mobile/app/(tabs)/settings.tsx
@@ -15,14 +15,16 @@ export default function SettingsScreen() {
   const storedHandle   = useSetting('handle') ?? '';
   const storedPath     = useSetting('auto_import_path') ?? '';
   const storedToken    = useSetting('api_token');
-  const storedSyncMode   = (useSetting('sync_mode') ?? 'summaries') as 'summaries' | 'full';
-  const storedSyncUpload = useSetting('sync_upload') === 'true';
+  const storedSyncMode     = (useSetting('sync_mode') ?? 'summaries') as 'summaries' | 'full';
+  const storedSyncUpload   = useSetting('sync_upload') === 'true';
+  const storedUploadFormat = (useSetting('upload_format') ?? 'raw') as 'raw' | 'bas';
 
   const [instanceUrl, setInstanceUrl] = useState(storedUrl);
   const [handle,      setHandle]      = useState(storedHandle);
   const [autoPath,    setAutoPath]    = useState(storedPath);
-  const [syncMode,    setSyncMode]    = useState(storedSyncMode);
-  const [syncUpload,  setSyncUpload]  = useState(storedSyncUpload);
+  const [syncMode,      setSyncMode]      = useState(storedSyncMode);
+  const [syncUpload,    setSyncUpload]    = useState(storedSyncUpload);
+  const [uploadFormat,  setUploadFormat]  = useState(storedUploadFormat);
   const [saved,       setSaved]       = useState(false);
   const theme = useTheme();
   const { paletteKey: palette, setPaletteOverride } = usePaletteControl();
@@ -213,6 +215,18 @@ export default function SettingsScreen() {
             ? 'Local activities are uploaded to the instance during sync.'
             : 'Local activities stay on device only.'}
         </Text>
+        <Text style={[styles.subLabel, { borderTopWidth: 1, borderTopColor: '#27272a', paddingTop: 12 }]}>Upload format</Text>
+        <View style={styles.modeRow}>
+          <ModeButton label="Original file" active={uploadFormat === 'raw'} accent={theme.accent} dim={theme.dim}
+            onPress={() => { setUploadFormat('raw'); setSetting(db, 'upload_format', 'raw'); }} />
+          <ModeButton label="Extracted JSON" active={uploadFormat === 'bas'} accent={theme.accent} dim={theme.dim}
+            onPress={() => { setUploadFormat('bas'); setSetting(db, 'upload_format', 'bas'); }} />
+        </View>
+        <Text style={styles.hint}>
+          {uploadFormat === 'raw'
+            ? 'Uploads the original FIT/GPX/TCX file. The server re-extracts it with DEM elevation correction and updates your local copy.'
+            : 'Uploads the pre-extracted JSON. Faster, but no DEM elevation correction.'}
+        </Text>
       </Section>
 
       <Section title="Palette">
diff --git a/mobile/db/sync.ts b/mobile/db/sync.ts
index 5e010b0..ab183dd 100644
--- a/mobile/db/sync.ts
+++ b/mobile/db/sync.ts
@@ -170,6 +170,7 @@ async function uploadLocalActivities(
      FROM activities WHERE origin = 'local' AND synced_at IS NULL`,
   );
 
+  const preferRaw = (await getSetting(db, 'upload_format') ?? 'raw') === 'raw';
   const headers = { Authorization: `Bearer ${token}`, 'Content-Type': 'application/json' };
   let uploaded = 0;
   let failed = 0;
@@ -182,9 +183,10 @@ async function uploadLocalActivities(
     try {
       let resp: Response;
 
-      // Prefer raw upload when the original FIT/GPX/TCX file is still on disk.
-      // The server re-extracts it with DEM elevation correction, producing better data.
-      const useRaw = row.original_path !== null &&
+      // When preferRaw is set and the original file is still on disk, send the raw
+      // bytes to /api/upload/raw so the server re-extracts with DEM elevation correction.
+      const useRaw = preferRaw &&
+        row.original_path !== null &&
         (await FileSystem.getInfoAsync(row.original_path)).exists;
 
       if (useRaw) {
@@ -211,6 +213,38 @@ async function uploadLocalActivities(
 
       if (resp.ok) {
         await db.runAsync(`UPDATE activities SET synced_at = ? WHERE id = ?`, [now, row.id]);
+        // Option A: after a raw upload, update local detail/timeseries/geojson with the
+        // server's DEM-corrected extraction so the app shows better elevation data.
+        if (useRaw) {
+          try {
+            const data = await resp.json() as {
+              id: string;
+              detail: object;
+              timeseries: object | null;
+              geojson: object | null;
+              source_hash: string;
+            };
+            if (data.id === row.id) {
+              await db.runAsync(
+                `UPDATE activities
+                 SET detail_json      = ?,
+                     timeseries_json  = COALESCE(?, timeseries_json),
+                     geojson          = COALESCE(?, geojson),
+                     source_hash      = ?
+                 WHERE id = ?`,
+                [
+                  JSON.stringify(data.detail),
+                  data.timeseries ? JSON.stringify(data.timeseries) : null,
+                  data.geojson    ? JSON.stringify(data.geojson)    : null,
+                  data.source_hash,
+                  row.id,
+                ],
+              );
+            }
+          } catch {
+            // Non-fatal: synced_at is already set, local data stays as-is
+          }
+        }
         uploaded++;
       } else {
         console.warn(`upload ${row.id}: HTTP ${resp.status}`);