From MB Wiki

The Forerunner 201 (http://www.garmin.com/products/forerunner201/) is a Garmin fitness GPS device that offers athletes an easy-to-read display, ergonomic wristband, and integrated GPS sensor that provides precise speed, distance, and pace data. It's a compact, lightweight, accurate training assistant with performance tracking, auto-lap, auto-pause and more.

Troubleshooting

Scenario & Question:

A friend and I rode a bike tour that was 205 miles. Both of our Garmins didn't pick up the first 70 miles of the ride. Very weird that it didn't register. When I left the parking lot, it was recording. In fact, it says 205 miles on the device. The Forerunner 201/301 was right on, but once downloaded to MotionBased, it missed the first 70+ miles.

Any idea what is going on???

Answer:

The easiest way to say this is that it may be time to upgrade your device. All devices have a maximum number of trackpoints in the active memory. The FR201 has 3,000, the FR301 has 5,000 and the Forerunner 205/305 and the Edge series have roughly 13,000. Once you reach the max trackpoint, the device will simply start recording over the beginning of the track log; it eats away at itself. In this FR201 example, the ride was too long for the FR201 active memory storage.