Sisted-in-law asked me to check the tyres in her 2017 1.2 110 bhp SE Fabia, as I often do when we visit her. I removed the factory steel spare wheel, which is full size and fitted with the same size tyre as the four alloy wheels; 185/60 R15. But it’s had thd yellow 80km/h speed restriction sticker like the skinny space saver spare.

Anyone any idea why?

It's because it is a steel wheel, not alloy!