To expose the road/outside properly you have to choices:
1. Autoexposure: The camera should point to the exterior through the windshield using spot metering (or even "center"). Doing this the Git2 will "ignore" what is not in the most center part so the exposure will be OK for the tones in that measured area. Of course you'll get darker tones in those part that are being ignored but is a tradeoff. Doing this you'll have OK exposure for the exterior and will adjust automatically while moving. So, point the camera in a way that the most center part of the image is the windshield. Your framing will change and your shoulder and steering will not appear much on the frame (depending on what metering you finally use).
2. Locked Exposure: Enter to the options and adjust the function "lock exposure & white balance" to the "side button". Then put the camera in the desired mounting position, aim it through the wiendshield to outside and check the screen, when the desired luminosity appears in the Git2 screen press the side button to lock those parameters and record with them (of course tigh the setup bolts in that moment). If the locked exposure is good outside will look nice, maybe inside will be darker but is one thing or another. Doing this you can keep your current framing so your shoulder and steeering will appear in the frame. The risk is that the locked exposure ends being too slow or too fast and...and then the tones that are out of reach will apprear over or underexposed.
(Probably in the future with a movable metering zone this will be easily achieved)
IMO it will look far better with a standard lens with Gyro ON. Ah, use Low contrast.