I decided to do a little test run with LapTimer before trying to use it at the track. I made a "track" by putting a POI on a public road in a location where I could do a complete loop without stopping. I mounted the iPhone in portrait orientaition, in close to a vertical plane. I got results, but the longitudinal acceleration values all hover around -1 G. This was normal driving, not racing. (I used my Mitsubishi Delica, to avoid any temptation to drive inappropriately!)
Was I simply not accelerating hard enough for the software to kick into the mode where it measures longitudinal acceleration? It seems as though it was measuring vertical acceleration -- i.e., along the longitudinal axis of the iPhone, not the car. Should I have mounted it horizontally?
Mounting Orientation and Longitudinal Acceleration
Re: Mounting Orientation and Longitudinal Acceleration
Did you start the app while already mounted in the final position or did you start it and then mounted it? You can also calculate the g-fprces from the gps data: go to "Lap Details" and look for the button at the bottom "Recalculate".