Found this app in App store that measures G force using the phone.
Above is the result using D mode in my Volkswagen Polo 1.2 TSI during daytime. If not mistaken the +ve G is the acceleration while the latter is braking. Seems that my braking G is harder than flooring the pedal haha.
The App is free and you have to mount the phone vertically on a phone holder to get readings. Please observe traffic instead of on your phone when trying this !