Why approve different size tyres for winter?

I have just had my one year old winter tyres refitted.

On checking the pressures I noticed that Vauxhall approve a different size for winter, whereas I'd had the same size as the standard eco tyres fitted. I'm confused.

Asked on 29 October 2012 by notapetrolhead

Answered by Honest John
A deeper, narrower tyre works better in snow.
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