ANY doughnut spare, not matter the size or position used is to be used ONLY for emergencies to get you to a place to get a proper repair done. They are not recommended to be used for more than 50 miles and not to exceed speeds of 50 MPH!!! Yet I have seen many people on the freeway flying along at 70-80 MPH with a doughnut spare on the car... That is soooo unsafe and just begging for problems.
If you want a spare that you can drive on like normal you need to get a full size spare with a properly sized tire as well... If you do get a doughnut spare, I hope you never have to use it. But if you do, be sure to use it properly... Also don't forget that you will need a jack and lug wrench to change a tire. Finally if you do have a flat, pull to a safe area before attempting to change the tire. DO NOT change the tire on the side of the freeway with traffic whizzing by at 80 MPH!!! Get well off the road, preferably to a parking lot or something like that where traffic will not be a factor in your safety!