Tried a new Satnav out today, MioMap v3.2 which is an i-Go clone, and low and behold it can log your journeys, more specifically it logs your journeys as nmea sentances, which is basic GPS data. This means you can use that data to workout your lap times

If you downloaded my VRoad software you'll need an updated version as (insert long boring technical reason here) ill get a new one uploaded as soon as and post the link, or if your feeling non techy, email me the log files and ill turn them into lap charts for you.
email is m a f f 6 6 7 @ g m a i l dot c o m
So if your off to buy a satnav, its something worth bearing in mind.
