Ive just bought my landy - first ever. It has these wheels fitted and a standard spare, im assuming that the spare is no good to use as the rolling radius will be different - is that correct?
Also if someone could identify what type of wheel this is - i'll get another for a spare if needed
If the spare has the same circumference around the tread, and the wheel fits the hub it should be ok. Condition needs to be roadworthy of course. and not driven like a nutter as the braking could be affected if the tyre is different tread and width.
other than looking a bit rubbish, it shouldn't matter too much as long as you keep your speed down and until you get the proper one fixed, unless you're miles from home!
thinking about those space-saver wheels on other cars, they are generally miles smaller than the standard wheel and are perfectly safe up to 50mph