If you've got a 205/60 now and you've got 5mm on each side of the tire to spare, there's no reason a 215/70 wont fit (unless you're low).
Cheers.
There's at least 5mm clearance on the width, but that 5mm would have to extend up inside the wheelarch to the height of the taller tyre, and this is difficult to measure, especially as I'd need to consider what hapens under suspemsion compression.
I suppose this one might be down to trial & error - unless of course someone out there's already tried and has the answer