If the spare tyre is very narrow then it is probably a temporary 'space saver', which obviously wouldn't be the same as the wheels/tyres on the car. But if the spare is of a 'normal' width, then it may simply be the case that the car has had alloy wheels fitted, either as an option or aftermarket. If this is the case, as long as the tyre circumference of the spare is about the same as those on the car, it will be fine. To be sure, let us know what the tyre sizes are, both spare and on the car. You are looking for something like this: 195/55 VR 15

Lots of cars have the spare as the 'standard' size, even if the wheels on the car itself are 'upgraded' to a larger size.

The critical point here is the rolling dimensions of the tyre and wheel combination - for example, a 205/50 R 15 is almost the same rolling circumference as a 205/55 R14.

As long as it's what it's supposed to be, then it's not a problem

My MK7 Fiesta 1.25 is fitted with 195/50 R15 tyres (by Ford). The factory fitted spare wheel is 175/65 R14. The spare wheel isn't a space saver.

However as the spare wheel isn't the same as the other wheels it's subject to a 50mph speed restriction when fitted. There is yellow sticker on the wheel to indicate this speed restriction.