Just a tip i picked up when trying to get into pillarless cars .If you prise open the drivers window a bit and wedge open with something soft you can get at the passengers side door locks across the car with a broom stick or similar bit of wood.
Measure the cicumference of the tyres with a piece of string..if they are nearly the same its not a problem.mismatched sizes can lead to diff trouble.
As long as the tyres are of similar quality it should be ok..
But in a moment of peril the mismatch may be the difference between staying on the road or disappearing into the bushes as We Are Borg states...