If they're anything like the white wall 'flaps' fitted to my ex's Nissan Figaro, you have to deflate the tyre, break the seal around the rim and then they MAY fit ok. Failing that the tyre has to come off.
On her car they caused abnormal wear on the tyre side wall: there was a ridge after only a few thousand miles. Things may be better on a van as they run higher tyre pressures and therefore have less 'bulge' at the bottom of the tyre (if you get my meaning), but as you may have guessed I was less than impressed by them...
