Your ride data is designed as a backup store in case you don't get an opportunity to upload your ride data at the end of a ride. It was never designed as a definitive "career history".
For these reasons, it is stored within the devices used to complete the ride, it does not sync between your iPhone and an iPad. If you like to keep your history and you are getting a new iPhone, you need to back up your iPhone (or iPad etc) to iTunes. When you then sync your new device, the ride history will then be restored.