Hi Robert,
I have a 2017 A4 Allroad, i have been looking for a spacesaver wheel as well, but have yet to purchase one, you will have to be aware that any spacesaver you
buy, will be compatable with revolutions per mile as the wheels fitted to the car,other wise, if the difference is too great, it may damage the quattro system.
here is a list of tyre sizes & revolutions per mile( the first one should be the tyre size fitted to your car) 245/45 R 18.=756.3 revs per mile.
225/55 R 17.=754.5.revs per mile. the spare that comes with the car, should be size, 175/55 R19,which equates to 759.2 revs per mile, which you can see, is
very close to the other sizes. i have seen a spacesaver tyre size= T125/70 R19. at 779.4. revs per mile, which is 20 more revs per mile than the original spare,
if it was not run for a great mileage it would most likely to be ok just to get u home, or to a garage. the next thing, is, will it fit in the car ?
let me know how u get on, hope this helps a bit.
Brian.