diff --git a/donkeycar/parts/imu.py b/donkeycar/parts/imu.py
index d1e5e2416..30ddef77f 100755
--- a/donkeycar/parts/imu.py
+++ b/donkeycar/parts/imu.py
@@ -179,13 +179,14 @@ def calibrate(self):
         self.pos = np.zeros(3)
         self.speed = np.zeros(3)
         tic = self.time
+        start_time = tic
         for _ in range(num_loops):
             self.poll()
             toc = time.time()
             if toc - tic < 1 / self.sample_rate:
                 time.sleep(1 / self.sample_rate - (toc - tic))
             tic = time.time()
-        self.speed_drift = self.pos / (toc - self.time)
+        self.speed_drift = self.pos / (toc - start_time)
         # reset internal parameters
         self.speed = np.zeros(3)
         self.pos = np.zeros(3)