You also need to make sure and never put a tire with a different overall diameter on the front, than the one that's already on it.
You can cause transmission/eCVT damage. Tire variations cause ratio changes between the two and force the transmission/eCVT
to run different axle speeds. Most might get by for a short term, but I wouldn't ever recommended it.
If necessary to use a spare tire, remove any tire from the rear and place it up front (for a mached pair) and place whatever spare on the rear
This will eleminate any chance of transmission/eCVT damage due to different axle ratio issues' with oddball tires.