Andy... you do mean for a 7, not a human powered vehicle? What's the current distance between the magnet and the sensor? Yes, there are lots of apps that display speed measured by GPS, many of them free. Definitely worth playing with. The position and mount are probably more important than the app. (I'm still looking for a good solution for fitting an iPhone just below the bottom rail of the dash, but that's probably a bit low for the main speed indicator.) (On most of our bikes I use the cheapest wireless Cateye that's available, but the last one wasn't quite the cheapest as we wanted bigger numerals on the display.) Jonathan