i keep mine on the roof rack till i buy a swing away or make a swing away cuz lifting up and bringing down 37'' tires is not my idea of user friendly lol but it would be best lower for reasons of ease,i wouldnt say as much about it throwing off your center of gravity cuz its not using up the entire width and legnth of your roof nor is your tire going to be three or four feet tall when installed on your rack lol
you can only prepare so much for a situation, what matters most is what you do when that time comes...