215/70s will be just as wide as 215 /60s, but substantially taller. I'd be more inclined to use 225/60s, if you can find them.
215 or 225 is the width of the "body" of the tire, in millimeters. 60 or 70 is the percentage of the height of that section, vs the width.
For example a 225/50-15 will be 225 mm wide, and the bottom of the wheel rim will be ~112.5 mm off the ground. (Nothing is exact, but that's a good ballpark explanation.)
To find equivalent tire sizes, go here...http://www.rimsntires.com/specspro.jsp
If you plug your "old" and "new" tire sizes into the chart, it will tell you how they compare in all directions, as well as the resulting speedometer error.