I'm guessing you're using the default T500 RS profile, if so then you need to edit your controller.ini in your userdata\player folder to this:-
Alternate Neutral Activation="0"
That setting will stick as long as you don't load a different profile, if you're trying out different stuff it might be an idea to save it as a preset (use a different filename) which will get saved to the userdata\controller folder along with the other default wheel presets.