Tyre sizes, does it matter?

[Scotties]

So I was driving home from work the other day and saw an advert at the local ATS for 30% off Mitchelin Tyres when you buy 4. As my tyres are fast aproaching the end of their life and this kind of offer doesnt come round every day I thought I would run a quote. I couldn't remeber the exact size (and Im too lazy to walk to the car) so I stuck my reg number on another site that would tell me and it gave me 2 options - 225/50 R17 and225/45 R17. I ran the quote for both sizes and I was shocked to find that the 225/50 R17 were nearly £50 a tyre more. When I checked the car I found that Audi have decided to give their customers the more expensive option. Now I know that tyres are the most important part of a car for stoping and handling so I dont want to endanger myself or other road users but will 5mm difference in wall size make much difference given I'm changing all 4 tyres?

Any help/advice would be much appreciated as it could save me £135.

 

[Spr0cket]

The sidewall is not reported in mm. It's a % of tyre width, hence the difference in wall size is not 5mm, rather 5% of the tyre width.

Most obvious impact will be to speedo accuracy as your adjusting tyre circumference.